Friday, October 15, 2010

Its dribbling ATF!.. why and the (temporary) fix

I haven't posted here in a couple of years (gosh, has it really been that long), not because I haven't been doing any wrenching (front lower ball joints and LCA bushing, trailing arm bushings, for example), but because the projects are significant enough that I'm sick and tired of car stuff by the time I'm finished and can't bring myself to post a writeup. However, this repair has stirred me out of my complancecy both because it didn't take too long, but also because it was a wakeup call to not be complacent and because there's a pretty decent chance it could go wrong with other's cars.. and they may not be as lucky as I was.

The Complacency

Hmm.. it seems to be leaking more oil than usual. Hmm.. it seems to be leaking a fair amount around the oil fill cap, and it's down a tad. One plus one equals two.. it couldn't possibly be leaking oil from someplace else. Well, its due for an oil change soon, so I might as well just top it off and find the leak when I'm under there changing the oil any day now. Repeat for a month. Stupid, stupid, stupid. If I think its leaking oil, I should figure out where. Its oil. Critical engine lubrication. And the oil cooler lines do go over time. If one pops, it can be catrostrophic for the engine (they don't like to run too well once they've pumped all their oil all over the ground). And at 3000RPM and 7bar, its gonna be dry before I can take my foot off the accellerator. Oh.. and my complancency didn't stop there either.. Noooo.. this time I went above and beyond and it could have cost me dearly.

A little while after that, I went to drive home one evening and noticed an oil puddle under the car. Did I peer under the car then? Heck no. I was running late for a meeting at my child's school and a school function (as long as I have to be there, the kill two birds with one stone strategy). Why is it major catastrophies always seem to happen to me on school function nights?

So what did I do? I started the car up and checked the gauges, especially the oil gauge. It was pegged like it should have been, so I drove off, figuring I'd drive home and park the car until I had time to find and fix the leak for real. A few blocks later and no oil pressure problems yet, but I checked the rear view mirror, just because I'm that extra paranoid (yet complacent.. an odd combination). And there, in the rear view mirror, I spotted a trail. A slight veer back and forth in my lane, and it is definately coming from my car.

So, that's when I finally checked. I pulled over, got out and leaned under the front of the car to see where the dribble was coming from. It was immediately obvious.. its dribbling so fast there's already little red puddle under the car. Diagnostic complete, its hemmoraging ATF and there's no way it'll make it home at that rate. Come to think of it, I'm not even sure it'll make it back to the lot at work where I can conveniently park it until I can trailer it home. See the nice ugly ATF trail it left all over the parking lot at work after I got it back there?

I figured it was a simple case of a rubber transmission cooler line dripping.. or in this case dripping a lot. However, first step, analyze the problem to be sure I was right. Sure enough, the transmission cooler line is dripping, but not not at the the rubber line where I thought. It appears to be dripping in the middle of the metal line, right at the mounting bracket that secures it to the engine with an oil pan bolt. However, this is also the low point of the line, so maybe the ATF is leaking someplace else and just dripping off here. So I started the car and checked again.

Under pressure, you can see ATF is squirting out of the metal line. The paper towels are there to absorb any ATF running down the line. If it were leaking up higher and running down the line, it would soak the towels and I'd know. I expected a dribble off the bracket, but with the ATF actually squirting out of the line the diagnosts step is immediately over. The metal line is definately leaking and right there at the bracket.

I took the mounting bracket off and here's the damage. You can actually see the pinhole in the line but I circled it for extra visibility.

The Repair

Now that I know what and where the problem is, I can figure out a repair. First choice, replace the leaking line. That would be my choice, but would take weeks for me to get the part and make the repair. The only place I have to work on my car for that long is in my gravel and dirt driveway. Worse, its a low spot in the yard. Even worse, a puddle forms there in our rainy season. Which is nine months long. And should be starting any day now -- in fact, it looks like the first front should be moving through in in the next few days. I need to get this fixed, and it doesn't look like I have time to wait and replace the broken line. So what to do?

I decided to splice the line with some transmission cooler hose and hose clamps. First step, get access to the damaged section. I need to disconnect the rubber line so I can get a tubing cutter around the damaged section of the line. Two wrenches prevents any risk of the rubber line being twisted. The metal line needs a 17mm wrench, the nut on the rubber line needs something slightly bigger, probabyly an 18mm. The oil pan bolt also needs to come out to get the bracket off. That takes a 5mm allen wrench or bit.

Next step, cut out the damaged section with a mini tubing cutter as shown here. I could probably have used a hack saw, but I had this tool and it leaves a much nicer end on the cut line than I'd likely be able to manage with a hacksaw. I wanted to cut the damaged section of line out so I could figure out why it failed and so I was attaching any repair to line with a full round cross section of known wall strength. I also wanted to leave a gap in the metal line so the ends didn't rub together inside the transmission cooler hose I was going to make the splice with and damage it inside. This may be a temporary repair to get me through till summer when I can replace the entire metal line, but there's no sense doing a shoddy job of it. It might have to last longer than I intend.

Here's the pieces for the splice, including the piece of damaged line that I cut out (I won't be using that, but it helped me size the piece of cooler hose I would need. The hose clamps are not the ordinary garden variety ones, but rather what are called injection hose clamps. They have a solid band and were recommended to me so I didn't cut into the hose with the clamps. They weren't trivial to find, but were a good idea. There's also hose clamps for soft silicone hose which would have also worked. Injection clamps are what was available at my auto parts store. I intend to double up the clamps on the end of each hose for extra measure.
I measured the external diameter of the metal line at 0.461 inches so got transmission cooler hose with an inner diameter of 3/8th inch, slightly smaller than the metal line it will go over to ensure a tight fit. Make sure to use transmission cooler line, not ordinary fuel line or some other line. Transmission cooler line is designed to hold against the pressure and heat of the hot transmission fluid (i.e. hydraulic oil).

A drop of ATF on the outside of the metal line helped the new coooler hose slip onto it. Here's the completed splice. I put the oil pan bolt back in temporarily, reconnected the rubber cooler line, and started to engine to check for leaks. Success -- no leaks. However, as expected, without the mounting bracket, the whole splice shakes around a lot. It won't last very long that way.

I can't use the original mounting bracket because it won't fit over the splice. Besides, it was the cause of the whole problem (I'll get into that later). I could use some metal strapping and fashion a bracket similar to the old one that would fit around the splice. However, it will be squeezing around where I cut the damaged section of metal line out. I could relocate it to one side by attaching to a different oil pan bolt, but that that leaves one end of the metal line unsupported except by the new splice hose. Given how heavy that line is, the unsupported end will shake around and probably cause an early failure someplace else. What I need is something rigid that straddles the gap and secures to both ends of the metal, kind of like a splint. It also needs to securely attach to the engine -- the oil pan bolt that the old bracket attached to is convient.

Here's the bracket I came up with. I made it from some 0.064 inch sheet aluminium I had lying around. One hole along one edge for the oil pan bolt, with that edge beveled away from it for clearance of the nearby oil pan bolts and to keep it from rubbing on anything. Four holes on the other edge for some zip ties that go around the splice. Long enough so the zip ties fasten to the splice where there is metal line inside it. I'd like to use something better than zip ties, but I couldn't come up with anything I liked -- small wire might cut into the cooler hose and large wire might be too stiff for me to secure tightly enough around the splice. I'll just have to keep an eye on them and make sure they don't get brittle and break.
Here's the bracket mounted to the oil pan. Since the oil pan bolt can't be tightened very tight or it might warp the pan and cause the gasket to leak, a dab of blue threadlock should keep it from coming loose.

And here's the completed repair with the new mounting bracket securing the splice to the engine.

Root Cause Analysis

Now that the leak is repaied and the car drivable again, I wanted to understand why the line sprung a leak. Did I or the previous owner hit something? Did it flex there, eventually causing a fatigue break?

Here's a picture of the mounting bracket. The bracket is very soft metal and bent to be larger than it was when mounted on the car. I slipped a red index card into it for the picture so the hole in it can be clearly seen. Next to it is the damaged piece of line oriented as it was inside the bracket. The hole in the line matches almost perfectly with the hole in the bracket. But neither looks damaged -- the metal is just very thin and worn through. Noteworthy is that the metal bracket wore though exactly at an inward-protruding bend. The straight edge on the bracket along that failure is the dead giveaway. Look at the first picture, before I messed with the bracket -- it looks like part of the install procedure involved squeezing the end of the bracket with a pliers or something to tighten it around the cooler line. The inward bend that created on the bracket eventually wore through the rubber shim around the line and then, metal-on-metal, the bracket eventually wore through the metal of the line until it sprung a leak.

Why did I want to figure all this out? Because the metal transmission cooler line on the other side of the engine has a bracket that looks exactly the same. That line isn't leaking, but its probably only a matter of time. Maybe not, but now that I know what happened and why, I know exactly what to check for. I can choose to either let things go and see if the other line springs a leak, or do some preventative maintence. I could, for instance, replace the rubber shim in the other bracket. Or I could decide to replace both lines instead of just the broken one when I do that job. It also gives me damage to look out for if I decide to get used lines (like from a junkyard) for the replacement. My car only has 172 thousand miles on it, these lines could have been intalled at the factory and never touched until now. Those lines lasted a good while, but if I look for used lines, I may have to find some that were not installed at the factory. As long as I can afford it, I think I'll plan on replacing both lines with new ones so I don't have to worry about them again.
Cheers, and consider checking you car for a similar latent problem next time you're under it.

Saturday, February 2, 2008

K-1 Spring Kit Replacement and Transmission Fluid/Filter Change


One of the earlier projects I did on my car was to change the ATF fluid and filter in the transmission. Since I didn't get any service records on the car when I bought it, I thought it would be a good idea to change them as most people are so scared of their transmission and therefore don't perform this required periodic maintenance. The transmission also slipped a little when changing from second to third, and there was a K-1 spring kit that was supposed to help with this problem. As long as I would be in there to replace the filter, I went ahead and replaced the K-1 spring kit too.

  • New transmission fluid. I used Mobil 1 synthetic, but they have since changed the formulation and it may not be an acceptable substitute for the Dexron II fluid the manual calls for.
  • Transmission filter.
  • Transmission pan gasket.
  • K-1 Spring kit

  • 26mm socket (I used a 1 1/16” socket, which is 26.9mm) It is helpful if this is a 12-point socket.
  • 18” breaker bar.
  • A very short socket extension. The shortest ones available were too long, so I used a 1/2”-3/8” and a 3/8”-1/2” adapter, stacked, to make a short extension.
  • Offset screwdriver. Slotted.
  • 5mm allen socket.
  • 13mm socket
  • Phillips screwdriver. The phillips end/bit for the offset screwdriver works best.


The general idea is remove the drain plugs on the transmission pan and torque converter and drain the ATF oil (fluid). Then drop the pan and replace the spring kit, filter and pan gasket. Replace the drain plugs and bolt the pan back on. And finally fill with new ATF.

I'll consistently refer to the automatic transmission fluid as “fluid” in the the text below because that is what most people think of it as. It is really just thick oil with detergents and dye added.


The K1 spring kit, for the 722.3XX automatic transmission in my 1983 300D turbo as it came from MB (via fastlane).

The wrench I used to rotate the engine via the harmonic balancer bolt on the front of the crankshaft. I've used a 1/2”->3/8” and a 3/8”->1/2” adapters to create a short extension. The extension is needed because the bolt is recessed pretty deeply in the pulley, but even the shortest extension was too long. There isn't much clearance between the radiator and the pulley, causing the wrench to bump into the back of the radiator when I tried it. These two adapters gave me just enough extension to reach the nut without there being much risk of banging into the back of the radiator. Reach up from underneath, slip the socket on the nut, and rotate away. The handle is my 18” breaker bar for the leverage – more would make it easier, less and you'd need to be a gorilla to turn the engine. The socket is a 1 1/16” socket – it should be a metric (probably 26mm?) but this works out to an exact 26.9mm. It fits a little looser than I'd prefer, but it was a 12 pt. socket (that's helpful) and I didn't have the proper metric convenient. I was OK, but rounding off nuts isn't fun, so if you're getting the socket, get the proper metric size. Turn only in the normal direction of rotation when the engine is running -- when facing the engine, the bolt turns clockwise. A 12-point socket is helpful because it allows the socket to be repositioned on the nut in 30 degree increments, which leaves it easily accessible from under the car when using the non-ratcheting breaker bar.

And this is why I messed with the socket above. I needed to rotate the engine until the torque converter drain plug was accessible through this little hole in the bell housing of the transmission. When turning the engine, turn just a little bit each time (~10 degrees) so you'll be able to see the plug before you rotate it past the access hole. Turn much more and you're likely rotate it past the the access port and have to go all the way around again like I did (it is not good to turn the engine backwards). On my converter, there's a small counter balance weight attached to it about where this plug is but on the other side -- when you see that go past, you know you're approximately 180 degrees away. The plug takes a 5mm allen socket. Other ways to turn the engine around are to bump it with the starter (fat chance the plug will stop exactly centered) or lever it around with a screwdriver, as had been done previously on this converter (it leaves little telltale tool scratches on the torque converter).

A closeup of the transmission pan drain plug. On mine, it's on the passenger side of the pan (see the picture of the removed pan below).

The 5mm allen socket needed for the torque converter and transmission pan drain plugs.

Clean the allen recesses in the drain plugs out and then remove them to drain the fluid out. The recesses generally get filled with dirt and grime, and can prevent the allen bit from getting a good purchase on it. If it slips out repeatedly, it'll round out the allen recess making it hard to remove the plugs. You need to drain both the pan and the torque converter because the fluid is about split between them.

The transmission pan has six 13mm bolts holding it to the transmission. To get to the location where the filter and spring kit go, it must be removed. Here's what mine looked like when I got it off. The good news is there's no sediment, the bad news is there's also no magnet to collect metal filings. The flat end of the pan is the end closest to the engine and torque converter.


The transmission fluid is syrupy when cold and continually drips off the bottom of the valve body so I didn't get an pictures of the process of replacing the filter as Ididn't want to risk killing my camera with a drip of oil. The filter screws to the bottom of the valve body with three phillips screws, and the location is pretty straight forward – there is only one thing that looks anything like the filter attached to the valve body. Nothing special with replacing it either – unscrew the old filter, set it aside someplace the fluid it in can safely drain, and screw the new filter on in its place. The screws on mine were in pretty tight but the offset screwdriver easily gave me the grip and leverage to turn the screws, even once the handle got all slippery with ATF. On my filter, one of the screws was cross threaded, and I just replaced it. I'll have to deal with that if I need to replace it again (assuming the transmission lasts another 30,000 miles).

K-1 Spring Kit

Drop the pan and this is what you see. This is facing toward the rear of the car. The front of the transmission valve body has all these little plates. We'll be removing the one on the lower right of this picture and replacing some parts inside it with the K-1 spring kit. Notice that it is held in by four straight-edge, round-headed screws.. an offset screwdriver will do nicely here as they are torqued fairly tightly, Interesting tidbit, on the left edge of the valve body one can see the transmission dipstick just sticking down.. normally it sticks down further but I have it slightly pulled out in case it needed to allow air into the system to help it drain.

Here's a closeup of what it looks like when the dipstick is fully inserted and clamped down. The fill lines on the dipstick are just visible and really tell the story of how critical the pan gasket seal is – the gasket will always be submerged below the AT fluid level except right after starting the engine while the fluid is still cold. A leaking gasket could easily allow the level to become critically low. This isn't relevant to the task, but I thought it was an interesting observation and picture that could be made only while the pan was removed.

Here's the offset screwdriver I used on the valve cover place and filter screws. Given the clearance at the spring kit cover, some form of offset or stubby screwdriver is required, but the extra leverage of an offset was definitely worthwhile as the screws of both are torqued fairly tight. Others have cobbled together an effective offset screwdriver using a small ratchet and socket that a screwdriver bit fits into. Doing the cobble trick with a torque wrench might be useful because then you could measure the torque on the screws when removing them and replace them to the same torque – as it was I could find no torque specs so I just guessed.

A closeup view of the cover that the spring kit fits inside.

I've undone all but one of the screws and left the cover hanging from the loosened screw. Luckily there was enough clearance for me to do this. I only did it because I was doing this in my dirt and gravel driveway and didn't want to risk any dirt getting on the cover while I was working. Under the cover you can see the little green piston holder. The internal spring has pushed it out a little here – making it very convenient to grab a hold of and slide out. There is sufficient clearance that I was able to remove and replace the green holder without any risk of damaging the two O-rings on it.

A closeup of the piston holder.

Here's what came out. The green piston holder and the internal spring mechanism. The stuff inside this holder is what we'll be replacing with the K1 spring kit.

Here's a picture of what was inside and how it was ordered. The small coil spring goes into the holder first, then the plastic-with-dual-spring valve.

The new spring kit pieces side by side with the old spring kit pieces. The large and medium spring go on the white post, the white post is (carefully and straightly!) inserted into the black piece until the assembly clicks and stays together on it's own. It takes some force, and if not done delicately or inserted at an angle, others have found out that the black piece can be cracked where the white piece is inserted. You can't see it in this picture, but the long spring is beefier and the short spring should be weaker since it is of the same gauge but has one fewer coil. The medium spring is about the same between both assemblies.

Here's the assembled new spring kit (bottom) ready to be replaced alongside the old one (top). Here, it can be clearly seen that the new long spring is beefier and the new short spring has one fewer coils.


Installation is the reverse of removal, so I didn't take pictures. Briefly, put the little spring in the green holder, put the black end into the holder and make sure it fits inside the short spring. Take the assembled thing and reinsert it back into the hole from whence it came. Push it in, slide the cover back over it, then put the screws back in and retighten them to about what they were before. I've found no torque specification on how tight to make the screws, so I just did it by feel trying to match the torque needed to undo them. However, a word of caution – the valve body is aluminum, so it wouldn't be too hard to cross thread or over-torque the screws and strip the holes. You'd have a really bad day if you did that, so take it easy.

Clean the pan edge where the new gasket will go and the part of the transmission where the gasket contacts it, reassemble with a new gasket and torque all the bolts to specification. The pan is just thin aluminum, and the gasket is a thick rubber one, so the pan will bend and the gasket will leak if you over torque the bolts. My gasket didn't leak, but if yours does, check that the gasket edge of the pan is flat – someone before you might have over torqued the bolts and bent it so it'll never seal right


Lastly, add the ATF as per MB's procedure and off you go. Don't forget that since the torque converter was drained, the fluid level will drop substantially after the engine is started for the first time and the converter gets refilled. So, expect a quick drop in fluid level and check it and refill a few times before driving off. As I recall, the MB manuals say the fluid level raises about 1cm between cold and warm. You'll be adding fluid when the transmission is cold because you can't drive it anywhere to warm it up until you've refilled it, so be careful not to overfill it either. If I recall the low mark on the transmission dip stick is about 1cm below the high mark, so maybe fill it when cold to the low mark and then drive it some and recheck before it is all the way warm.


In my case, the spring kit didn't make any difference. Others report that it fixed the 2-3 shift slip that they hadn't been able to fix with adjustments. In my case, I didn't expect it to fix anything since I haven't gone through all the possible vacuum and other adjustments that can be made yet. I replaced it because I wanted to do the fluid/filter change before the cold weather set in. I certainly didn't want to find out come spring when I adjusted the transmission that I was going to have to drain it and drop the pan on it again just to replace the spring kit.

There is a slight difference in shifting, but I'm attributing it to the fluid/filter change since it is very slight. The transmission also seems to slide from gear to gear a little more smoothly than it used to, and that could be because I used synthetic fluid.

All images and text Copyright 2008.

Tuesday, January 15, 2008

Replacing the plastic key head with a wooden one


Recently, the black plastic head for my key finally tore completely off. After using the key without it for a couple of weeks, I decided it was time to do something about it. While perusing my favorite Mercedes wrenching site, I found this thread,, where one of the members had replaced the plastic head with some wood. A suggestion was made that some nice zebra wood to match the interior trim would be nice. Since my head needed replacing anyway, I embarked on the following project to replace it with a nice wooden one. With replacement heads being only about $3 I didn’t save any money, but that wasn’t why I did this project.

All in all, I think the key turned out rather nicely, pretty much just like I wanted it to turn out.

Picture 1: Finished key

First I’m going to outline the steps I took. After that I’ll point out all the mistakes I made and what I did, or could have done, to correct them. Lastly, I’ll include a few woodworking tips for those non-woodworker gearheads that might be interested in trying this project themselves.

The entire project probably cost me about $80 since I had to buy all the supplies and didn't cut corners to get the desired result (the mirror finish epoxy, for example, was ~$30 alone). I did it anyway because I wanted experience with the materials and finishes, I thought I’d like the result, and I wanted to practice my dormant woodworking skills.


  • Dremel tool with tear-drop shaped burr.
  • Jewelers saw (or fretsaw, jigsaw, or even a hacksaw).
  • Drill, at least ¼”.
  • Rattail file or small riffling files.
  • Coarse flat file.
  • Two small disposable artists brush.
  • A small chisel.
  • A vise.


  • 1/8" thick wood.
  • Thick gap-filling, two-part epoxy that isn't runny when mixed.
  • Finish. I chose a two-part mirror finish bar coating epoxy.
  • Denatured alcohol, used to clean epoxy off surfaces, even once cured.
  • Some paper. Thick, brown paper or several layers of newspaper will do nicely.
  • Sandpaper. I used just a single grit of 320 and found that it sanded the wood plenty fast enough.


This project isn’t a quick one, mainly because of my use of epoxies for glue and the finish. I compressed the timeline into just under a week and it was half as long as I should have taken.


The overall process is to cut some key-head blanks from some thin wood and sandwich the key between them. We carve out a mortise (pocket) between the blanks for the key to fit into, epoxy the laminations together with the key inside, and then finish it. Sounds pretty simple.

STEP 1: Select the wood

Picture 2: 1/8” thick Bolovian Rosewood

My local woodworkers store sells dimensional, surfaced, exotic hardwoods, including zebra wood (what Mercedes calls zebrano). The pieces come in 3" x 24" and varying thicknesses -- I chose the 1/8" thickness because two layers of it were a pretty close match to the thickness of the plastic head, eliminating the need to plane it thinner. They were out of the 1/8” thick surfaced zebra wood when I went, and not wanting to wait, I selected some Bolivian Rosewood because it had a fairly strong grain and I liked the warm tone of it. The exotic hardwoods run about $13, but they also had some really nice figured “domestic” hardwoods that I almost chose.

STEP 2: Layout Key Head Blanks

Picture 3: laying the key head on the wood

Picture 4: Four blanks laid out on the board. Two will be needed for the project.

Lay out some key head blanks on the wood, and cut them out with the jewelers saw. Do the layout so the grain runs sideways along the key (perpendicular to the key shank) like shown for strength. Use the plastic head to size the blanks, but make them a little oversize.

STEP 3: Cut Out the Blanks

Picture 5: Rip cut first

Picture 6: Cross cut next

Cut out the blanks. Make one edge straight as a reference edge for laying out the mortise.

Picture 7: The two blanks that will be used

The two blanks that will sandwich this key.

STEP 4: Mark the Key Shank

Next put the key into the plastic head and mark a line across the shank, then pull the plastic head off the key shank. We’ll need it again for later steps, so don’t mangle it too badly getting it off (assuming getting the plastic head off will require any effort anyway).

STEP 5: Lay Out the Mortise

Picture 8: Laying out the location of the mortise

Use the line across the shank and the straight edge on the blank to lay out the mortises in the blanks.

STEP 6: Carve Out the Mortises

Picture 9: Test fitting the key in the mortise. Not quite deep enough yet.

Use the Dremel tool with the burr to carve out the mortise in each blank. Make sure that the two blanks fit together flush with the key between them.

STEP 6: Glue the Lamination Together

Glue the laminations together with some of the gap-filling epoxy so the key is held tight in the head. Spread the epoxy into every cranny of the mortises and over the entire faces to be glued together, then embed the key in it.

Picture 10: Clamping the laminations together

Gently clamp the laminations together with some paper between the lamination and the blocks of wood to keep the squeezed out glue from gluing the key head to them. Pictured here is the key, shank sticking up, clamped in the vise.

STEP 7: Clean Off Excess Glue and Test Fit in the Locks

Picture 11: Fresh out of the vise. There’s a big glub of glue to be removed.

And here’s the key with wood head after letting it cure overnight. Trim of any excess glubs of glue using the file or chisel and test the key in all the locks of the car – some locks (especially the trunk lock on my car) need more clearance than others.

STEP 8: Layout the Desired Head

Picture 12: Desired head laid out and marked for visibility.

Next, position the plastic head on the blank and trace the outside to get the shape of the head.

STEP 9: Make the Keychain Hole

Picture 13: Drilling out the ends of the keyring hole.

Picture 14: Sawing out the remaining wood between the holes.

Drill and saw out the wood from the interior of the hole through the head.

Picture 15: The rough keyring hole.

STEP 10: Shape, Round Off and Sand

Shape the outside with the flat file and the inside of the hole with the rattail file. When you have the desired shape, sand the wood smooth with the 320 grit sandpaper.

Picture 16: The shaped, smoothed and sanded key head.

STEP 11: Finishing

Mix up a small amount of the bar-finish epoxy and paint it on the wood.

Picture 17: The key immediately after painting the expoy finish on.

STEP 12: Let the Finish Cure

Picture 18: The finished key after the finish has cured.

And here is the finished coating. It still has that extra glossy look that matches the interior wood trim in the car.

Once the finish is cured, check that the key fits in all the locks of the car again and remove any excess.


Since I had to buy all the materials I certainly didn’t save any money, and my choice of materials and finishes made the cost quite a bit more than it could have otherwise been. However, I think my key turned out rather nicely and I enjoyed learning some new woodworking techniques and materials, which was pretty much the point of this project for me. I now have a nice conversation piece and enjoy the tactile feel of the smooth finish whenever I use it.


I’m certainly no master woodworker and my finished key shows it. I made mistakes nearly every step of the way, some of which I expected and planned for, but others I didn’t and had to correct for along the way. In this section I’ll point out all the mistakes I made and how I corrected them as I went along as my way of illustrating that one does not need to be terribly skilled at woodworking to end up with a nice looking key head.


When I laid out the key head blanks, I knew I needed a straight edge to reference the key shank position against. I decided to use the straight edge of the surfaced wood for this, but didn’t notice that it had been dyed a dark color. Luckily, my key shank ended up deep in the wooden head and I had to file down the wood on that edge for clearance in the locks, thus removing most of the dyed wood. Also luckily, the remaining dyed wood is in the least visible part of the head, the one facing the key shank, and because of the curve of the key head, dyed wood only remains close to the shank where it is least visible.


I went through a couple of false starts trying to get the mortise formed in the blanks. First, I tried putting the sandwich in a vise and crushing it together.

Picture 19: Attempting to crush the mortises into the blanks.

Here is the sandwich being crushed. This didn’t work at all. If I had used thick blocks of recently harvested, soft pine, it would have worked. I put a fair amount of pressure on the sandwich and the key barely made a dent in the blanks because the wood is just so hard.

Next, I got out my smallest chisel and figured I chisel out a mortise like you see in the woodworker shows on TV. I proceeded to score the outline with the chisel by tapping straight down into the blank, and all went well until I tried to score an edge with the grain. Then the chisel just split the wood along the grain and popped the small piece into two. I cut four blanks in the beginning because I figured I’d break a few trying to cut the mortises, so I just grabbed another and tried a different way. If I had to make this method work, I’d use some glue and paper to stick the blank to a larger block of wood to keep it from splitting.


When I finally got the mortise carved out with the Dremel tool, I did such a poor job that the key slopped around a lot.

Picture 20: Blurry picture. See how my mortise extends beyond the key.

Sorry for the blurry picture, but I wanted to show how sloppy of a job my mortise was. It got even worse because I had to grind it more so the reference line on the key shank fit all the way to the edge of the blank. This isn’t really a mistake as such since I expected I’d do a sloppy job. This is why I chose to use two-part gap-filling epoxy to glue the halves together. I knew my mortise would be sloppy but that the epoxy could fill the gaps and be stronger than the wood itself. I just had to make sure the epoxy was well spread into all the crevices of the mortise before embedding the key in it.


When I made my mortises, there was so much slop that the key shank could move every which way – side to side, tilt and rotate and even in and out of the head. As I mentioned earlier, in mistake 3, I did plan for this and chose gap-filling epoxy for my glue. As shown in step 6, I braced the key into position in the vise with some cardboard. So far, all was expected and planned for. My mistake was that I forgot that the key shank could slide around in the mortise so that the reference line on it slides inside the key head. When I clamped it in the vise with the shank pointing up, this is exactly what it did. I later caught and corrected this when I test fit the key in the locks of my car and had to trim down the edge with the shank sticking out with a file.


In step 7, the photo shows the key shank sticking out of the head at an angle. This is another place where I didn’t intend for this mistake, but had expected something like it might happen. Back in step 2, where I laid out the blanks, I purposefully made them a bit oversize, just in case the key shanks didn’t end up perfectly centered in the head. In a more perfect world, I’d have made the blanks just a little larger, but it turned out I had just enough extra room so I was OK. To fix this mistake I rotated the plastic key head as I laid it out on the new head in step 8.


In step 9 where I made the keychain hole, I made a mistake in judgment that caused me to make a whole series of mistakes – I decided to try to duplicate the oval hole in the plastic head. This resulted in the wood head being thin on the sides of the keychain hole, right where it is across the grain and the wood is weakest to begin with.

Choosing to do the oval hole also caused me to decide to drill two holes at the sides. I figured I’d get a nice round curve from the drill at those ends and could cut out the middle with the jewelers saw. For some reason, despite using a drill press and a cross sliding vise, I didn’t quite get the two holes exactly where I wanted. Then I had to use the rattail file to clean up the hole. I’m not very good with a rattail file and ended up going too deep and having to repeatedly enlarge the hole, further making the sides of the hole weaker.

So far the head hasn’t broken. Yet.

I didn’t fix this mistake. I’ve given some thought about it and come up with two solutions. The first would be to not try to replicate the oval hole and instead just use a large round one. This would have been easy to make with a larger drill and then I wouldn’t have a rough hole to clean up and smooth out. It is too late for my key, but I’ll do this on the next one.

The second solution is to reinforce the sides of the key head with some brass. I can apply this to my key and am considering it. As I see it, the basic idea would be to cut a slot in the edge of the key from top to bottom with the jewelers saw. Then epoxy a piece of brass in the kerf and file it to match the profile of the key head. There will be a tradeoff with the saw – a wider kerf will allow a thicker piece of brass and strengthen the head more, but it will also weaken the head while trying to make the kerf, possibly to the point of causing it to break right when there’s very little wood to piece back together.


This is a minor mistake, but when I went to finish the key, I mixed up enough epoxy to coat about 10 keys, and then ended up throwing the extra away. Six to nine drops would be more than enough.


I applied too thick of a coating of the finish epoxy and it dripped off, and even cured with some drips. This happened partly because I mixed up so much epoxy, and partly because epoxy, even the fluid kind I selected, is thicker than paint. It may have been thick, but it flowed for an extraordinarily long time (hours) because it was designed to be a self-leveling, pourable finish.

I don’t have any pictures of the back side of the head, but it has some drips of epoxy in it. I haven’t fixed it yet because they are not large and don’t bother me, and I just show the other side to people J. If I wanted to fix it now that the epoxy has fully cured, I could file or sand the bumps off and then either try to polish the finish by wet sanding up through 1500 grit and then polishing with compounds, or put a very thin second coat of epoxy over the entire key.

Better yet would have been to only put a thin coating on the entire head the first time, then, once it was cured enough to put on a second coating (about 2 days), then flip it over and put another thin coating on the entire head. This is why I suggested two brushes in the materials list. You might be able to clean them out with denatured alcohol before the epoxy cures if you want to try.


This is probably the worst mistake I made on the entire project because I made it after everything was done. What was so horrible? After letting the finish epoxy cure for only two days, the finish felt hard to the touch, so I picked up the key and pocketed it. Oops, big mistake. My body heat warmed the finish and made it soft enough to allow the fabric of my pocket to make an imprint in it as shown in the picture (notice the bumpiness of the reflection in the picture below). I had to set the key aside for another 2-3 days for the finish to cure the rest of the way.

Picture 21: I ruined the finish by not waiting long enough for the finish to cure
Like the drips, I’d repair this by either sanding smooth and polishing or just putting on a second coating of finish.


The project is done and ready for use but I still found one last mistake to make. I put a big scratch in the finish while putting it on my keyring. It is one of those split rings, and I didn’t think to protect the key as I worked it around and onto the ring. Next time I’ll wrap some paper or something around the top edge of the keyring hole to prevent this.


I’ve certainly not a master woodworker so none of my tips will be new to fellow woodworkers, but I’m going to provide a few woodworking tips for those non-woodworking gearheads out there that might be interested in doing this project.

So, straight from a barely competent woodworker (me)…
  • Make sure the tooks are oil and grease free. The oils will soak into the wood while it’s being worked and prevent the glue and finish from sticking to it. I use many of my tools for both woodworking and automotive work, so I just make sure they are cleaned off before they touch wood again.
  • Account for the width of the saw kerf when laying out the blanks.
  • The size of the teeth of the saw is critical for this project because of the thin wood used. The rule of thumb is to have at least three teeth engaged in the wood all the time. The support of the other teeth helps keep the saw from catching on the wood and jumping around. If you don’t have a saw with fine enough teeth, cut through the wood at a slant so more teeth are in contact with the wood at any given time.
  • When using the flat file for creating the straight, reference edge on the blank and for shaping, I had a lot more control by holding the file perpendicular to my body with the handle in my stomach, then pulling the small pieces of wood toward me along the file.
  • Some woods, especially exotic hardwoods, have natural oils in them that hinders glue and finish adhesion. Wipe them off with denatured alcohol before applying glue or finish.
  • This is probably just me being paranoid, but denatured alcohol absorbs water over time which is left behind when the alcohol evaporates. Glues and finishes won’t adhere to wet wood so give the wood a good while after wiping it down.
  • Denatured alcohol is a solvent for epoxy. So it can be used to clean up remaining films of epoxy when trimming it away from the key shank. Doing this is a good idea because it might otherwise scrape off in the lock and make it stick.
  • I’m not very good with a rattail file, but I finally figured out that filing at an angle to the face of the head rather than perpendicular it caused the file to not make grooves so easily and also allowed me to change the angle of the strokes to remove the high spots.
  • When mixing epoxy, use the two pot method. Put the components together into one “pot” and mix them thoroughly, then move the mixed epoxy to a clean “pot” and mix it thoroughly again. This helps eliminate there from being any resin that has no hardener at all mixed in as happens along the sides of the first pot. The resin remains sticky for a lot longer if there isn’t enough hardener mixed in and may even never harden. It is recommended to mix the finish epoxy this way so it all hardens at the same time.

That's it.

Wednesday, October 10, 2007

Automatic Climate Control Unit Repair

I haven't had time to post some of the older tasks I've done, so I'll just jump in with what I'm doing these days...

Task and Diagnostic Procedure
This task about repairing my automatic climate control unit (the ACC). These have a typical failure mode were some internal solder joints break, rendering it partially functional. Different units break different solder joints causing different failure modes, but one of the most common is that only defrost works, and often only works for a while after starting the car. This was exactly how my car worked. The non-technical diagnostic procedure is to wait until the ACC is in its failure mode, and then give the front of it a whack to see if it starts working again for a bit. On mine, that would cause defrost to start working again, for a while at least. Note that there is another unrelated failure mode where wiggling the ignition key restores functionality for a while -- if yours responds to this procedure, then this repair probably won't help you.

The repair for this unit was to use a soldering iron and reflow (remelt) the solder. To get to the joints requires disassembly of the unit, so that's what we'll do.

Tools Needed
To do this repair, you'll need the following tools:

  • Flat blade screwdriver
  • Phillips screwdriver
  • penknife (my tool of choice for easing click-together plastic latches apart)
  • needle nose pliers
  • soldering iron
  • rosin-core electrical solder


Step 1: Remove the fancy wood-grain front. I don't have a picture of this, but it is held on with friction pins that fit into the holes circles in
red. Above the radio (the radio bezel may have to be removed to access them), are two flat-blade screwdriver slots in the the bottom of the bezel for you to
gently pry it off with. The friction pins fit into the holes circled in red in this picture.

Step 2: Remove the unit from the car. There are two screws (circled in green) that need to be removed. After that, on the w123, the unit will hinge
forward on its bottom edge until you can lift it out. There are two large multi-pin cables attached, one on each side, that need to be
unplugged from the unit.

Step 3: Remove the front, plastic mounting bracket from the unit. Three screw (circled in purple) hold it on.

Step 4: Next, remove the temperature wheel It plugs into a set of pins on the side of the unit like the cables did, and has some little plastic tabs
holding it in place. Gently (!) squeeze the two white plastic tabs together using a needle nose pliers just enough to get them to slip down
the hole (see orange circle and arrows) and ease the temperature wheel unit off. Don't force these tabs, and don't squeeze them together too hard or that 20 year old plastic will break.

Step 5: Remove the cover of the fan switch unit. The switch unit can't be removed yet because the buttons lock it to the front piece. Taking the
cover off makes it easier to remove the buttons. The cover is held on by two tabs, one on the top (see purple circle) and one on the bottom.
Gently ease the cover off past the tabs. I prefer a penknife for these kinds of operations as they are thin enough to slip between the plastic
parts without mashing and marring them too bad. Just be careful not to slice pieces of plastic off.

Shown here is the unit with the temperature unit removed and the cover of the fan buttons removed.

Shown here is the inside of the fan switch unit. The "T"-shaped piece of plastic is held in by the cover. If it fell out when you removed the
cover, this picture should help in getting it back together correctly when you reassemble. The round pivot in the middle is different lengths. When you reassemble, just be sure the fingers of the "T" fit into the backs of the switches like shown here.

Step 6: The next step is to remove the buttons and the front piece. The way I did this, they sort of need to be done together -- the front piece can't
be removed until the buttons are off, and I couldn't figure out how to pull the buttons off so I had to pop them off from behind, which I couldn't do until the front piece was off. The next two pictures show where the tabs that hold the front piece are -- here is one on the top (circled in blue) and two on the bottom (circled in blue on the next picture). Pop them them apart, but the front piece can't be removed yet because of the buttons. However, popping it free allows just enough access to slip the penknife in behind it and pop the buttons off by pushing them from behind and shown in the next picture. The fan buttons can be easily popped off by pushing from behind.

Shown here are all the parts removed so far. The rest of the disassembly is pretty easy from here on. Note also the clear plastic light pipes across the front and down the side of the fan switch unit.

Step 7: Next remove the bottom plastic panel. I've reused an earlier picture to show where the three tabs on the back that hold it on are. Once released, it hinges up toward the front until it can be removed.

Step 8: Finally, with the buttons off and the front piece removed, the fan button unit can be removed. Press the two tabs by the purple arrows together just until they clear far enough to slide out and allow unplugging the fan button unit from the side of the climate control unit.

Step 9:The plastic cover over the internal circuit cards can finally be removed. The circuit cards and guts hinge down and out from under the cover. Once the cover comes off, the two plastic pieces with pin numbers that the side pins stick through can be slipped off.

And here's the wrong ACC unit in all it's stripped glory -- yours from a w123 won't look exactly like this one (this one's from my practice w126 unit). There's a main base board, the top daughter board, and the two side wing boards with the pins. BTW, the w123 unit only has 4 relays instead of the 6 shown here, and the circuit traces are slightly different, but otherwise they look pretty much identical.

The Repair

With the unit disassembled, the repair can begin. Some have reported that they had cracked circuit traces on the daughter board where the pins from the front panel switches connect. Mine were fine there, but had cracks where one of the wing boards connects to the main board.

Shown here are the cracked solder joints on my unit, circled in red and with arrows pointing to them. I've even slipped a small piece of yellow-green paper down one crack to prove to myself that it was indeed not connecting reliably :). The solder on these needs to be remelted with a soldering iron, and maybe a little more new solder added, to rebridge the gap.

And here's the repaired solder joints, circled in blue.

Failure Analysis
I'm certainly not officially qualified to do a failure analysis, but I've had years of experience taking things apart and fixing them, often trying to make them better so they won't just fail the same way again. So, as long as I was in there, I figured I'd take a look and see if I could figure out why those particular solder joints had failed on my particular unit. Sure enough, there was. When my CCU was soldered together, the wing board with the cracked joints was bent and the solder was used to hold it in place. This put permanent tension on the solder bridges. Unlikely that the tension alone caused the failure -- it was probably the the vibration of the car and that heavy cable hanging off those pins that did it. However, the tension made them spread once broken and certainly helped propagate the cracking down through more of the bridges.

A Better Fix
Using lead solder as a mechanical attachment isn't a great idea as it tends to bend, stress fracture and disconnect. I tried using it for that a lot as a kid and it always failed in short order. So how to fix it to be better? Replace each solder bridge with a small length of stranded wire. Make sure that the solder doesn't bridge the gap so there is no mechanical attachment via it -- if there is, that bridge could break such that both ends of the wire are on the same side. I certainly didn't do this. Instead, I completely unsoldered that wing board, repositioned it so I wouldn't need to flex it as I resoldered it, and then made new solder bridges to hold it on. I figured the bridged on the other wing board (the one not flexed) had lasted 20 years, so this would probably be good for another 20 years now.
I also went a bit further and reflowed all the solder of all the joints on all the boards. Sometimes solder joints can have pratically invisible cracks through them in my experience. I figure it was easier to reflow all the joints then have to disassemble the unit again to repair some other failed joint.

I didn't take any pictures because there was nothing interesting. Just reverse the disassembly steps and it all clicks together. At the time I did mine, I didn't clean the pins and reassemble with dielectric grease, but that might have been a good idea. The only tricky part I has was remembering how the buttons went back in. They all have a side were the clear plastic inside them is exposed on one or more sides -- make sure you pop them back on such that the exposed clear plastic edges face a light pipe (I don't think they'll go on wrong, but I didn't try).