marlinspike

I have a Mercedes, but as I understand it the 928 also used the Mercedes 722.3 transmission and also had B2 piston issues. I'm looking for someone to replace the B2 piston on my trans. I am capable of doing it myself, but I rather not if I can afford it. Unfortunately the MB shops won't do it saying they "don't repair transmissions, only replace them." Anybody know a shop here in The Tidewater that can do this?

Landseer

There is a guy, 928fixer, that occasionally posts here, that clearly from his commentary is a skilled mechanic. Maybe send him a PM message?

I just did a B2 replacement. Interesting job. Not too bad. Parts will run you about $150. Roger has them.

In case you want to see it.

https://rennlist.com/forums/928-foru...ly-4-spd.html#

UncleMaz

Are you only going in reverse? If so, your B2 piston can be broken or your thrust pin out of spec. Feel free to PM me with your email for documents that may be very helpful.

marlinspike

Works in reverse, but you can also, very gently, move forward, and of course once you get the trans past 2nd gear (helped to take the line off the vacuum modulator and expand out the throttle position bowden cable) it is of course fine.

I think I've read just about all the documents, it just won't be too fun doing this on my back in the cramped quarters of an apartment garage (private garage, but it's barely bigger than the car)

UncleMaz

I can still remember cold drips of ATF on my face last January in our cold, dark apt. building space.
Have you inspected your pan yet? My reaction valve thrust pin was in my pan when I inspected it. What model MB?

marlinspike

1985 380SE...kinda...transmission is anyways.

Haven't gotten the pan off yet. If I'm going to pay someone to do it, I figure I'll pay them all the way, and if I'm going to do any of it myself, I'm going to do all of it myself. Price is going to determine this, so I'm waiting to get some quotes first.

marlinspike

BTW, one thing that might be worth mentioning - in D at idle (or slowly moving along, i.e. still in 1st gear, I don't know if it does it in the other gears or not) you can hear a light rattling noise coming from down there. Does this give any hints as to what specific aspect of the B-2 assembly went bad?

UncleMaz

Only a guess, but the piston is broken or the the thrust pin is loose. Since your car is a pre-1992, I would bet the piston is the old type and broken. This does not mean your band is not out of spec. I would make sure whoever does the repair, checks the band itself for spec and for any cracking.

marlinspike

There's a Mercedes shop on the southside that says they'd do it for about $160 of labor (said he's done them before but it's been a few years). Seems worth it.

UncleMaz

That is an excellent deal. Parts aren't too bad either. I think the piston (if broken) is like $140 and the pins are about 12 bucks a piece (if needed) If the B2 band girdle is broken, I think that was about $16. Plus fluid and filter ($60-$70).

I would not have bothered for $160 labor charge. I had to do it twice before the B2 band was ultimately out of spec and I had to put in a used trans.

marlinspike

What exactly is the 5.2mm to 5.5mm of play this post is referring to when talking about the dog-bone?
https://rennlist.com/forums/7057066-post4.html

UncleMaz

B2 thrust pin lengths vary depending on how in or out of spec your B2 band is. The dog bone is the thrust pin. I have the WSM B2 band adjustment PDF sectioned out. If you want it, I can email it. It is about 450k.

marlinspike

Ah, yeah, I know what the dogbone is but I was wondering how the play is measured. If you could send it to rrshayegan at wm dot edu I'd appreciate it. The only thing the MB manuals tell you about the trans relate to changing the fluid.

UncleMaz

Document sent.

Landseer

I think you are measuring the distance between the yellow arrows two times and taking the difference.

First, with the B2 piston and the brake band all the way right and the band bumped up against the dogbone, then again, after closing the band by hand.

See if that's what the manual shows.

Not shown here is a yellowish-white brake band guide, big plastic piece, that covers this area. It needs to be removed to get to the band.