Saturday, February 2, 2008

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

INTRODUCTION

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.


PARTS NEEDED
  • 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

TOOLS USED
  • 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.

PROCEDURE OVERVIEW

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.


PROCEDURE

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.



FILTER

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

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

REFILLING WITH ATF

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.

RESULTS

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.