Bill Ball

Well, I was getting ready to reinstall my 89 auto trans after having it "partially" rebuilt and I found something I'm not sure about.

I was cleaning it up a little and noticed the cover on the B2 piston, which had not been touched during the rebuild, rotated easily. I thought it was supposed to be spring loaded, and needed to be pressed in against the spring to remove the retaining ring. Should I be concerned? A search for "B2 piston" shows that it's easy to remove the cover and have a look at the B2. Suppose I should do that.

This was a "partial rebuild" since the tranny worked well excepting a leak from the TC. So, the front seals and o-rings were replaced. The B3 piston was replaced due to a broken locator pin and the friction plates in the K1 clutch pack were replaced. That's about all.

Mrmerlin

Bill there may be an updated part for the B2 piston its been a while since I redid my trans and IIRC that was a part that was swapped out also replace the O ring use DC111 on the O ring

Bill Ball

Good point, Stan. There is an updated B2. I wasn't sure if that update had already been implemented in 89 or if it was later, but I gather that there was a final update in 94 from reading the 3rd document in this thread: https://rennlist.com/forums/928-foru...placement.html. As I said back in 2006 in that thread, it was a "keeper". I had the documents saved in a tranny info folder on my hard drive.

Regardless, the cover o-ring must be bad to allow the cover the rotate easily by hand.

I'm just a little puzzled as to why there is no spring pressure against the cover. Could the rebuilder have reassembled the B2 band improperly? I need to call him - I'm not sure he even got back into that area since this was mostly a front area rebuild. I'd hate to reinstall this tranny and then find out it needs to come back out. I gather you can see the band and the dogbone engagement if you partially disassemble the valve body. Darn. I already have the torque tube on and the tranny halfway back in.

Here's what one guy found: https://rennlist.com/forums/928-foru...d-b2-band.html I hope I don't have to go this far or further.

karl ruiter

I replaced my B2 piston pretty recently and the cover rotated pretty easily before and after. You might or might not want to replace the piston while you have the tranny out, but it would be worth checking it at least of the rebuilder did not.

borland

Bill,

Are you sure your not mistaking the governer cover for the B2 piston cover? B2 piston spring and pin, if installed correctly, should not allow the cover to spin freely. The spring on B2 is much lighter than the B3, so you can remove the cover without the special press tool required for B3.

The B2 cover is easy to remove. Don't try that with B3 however. If you remove the cover, just be very careful with the reinstallation, making sure you don't pinch the o-ring. The o-ring should be coated with ATF upon installation to promote installation and provide a good seal.

If you replace the o-ring, only use one from a Mercedes dealer's part department. They should stock all o-rings for the 722.3. Mercedes part numbers are used in the PET, but Mercedes should be able to idendify them regardless.

Bill Ball

The rebuilder says it is normal. He didn't touch that area. And you found the same thing, so that is reassuring. This seems to be in conflict with the descriptions in Mercedes tranny service documents and some other threads here where spring pressure against the cover is mentioned as well as the cover being rather tightlty held. There is an o-ring that you'd think would grip the cover unless the o-ring is worn. I'm not too concerned about that o-ring as the piston is sealed further in so there should not be a fluid leak. Although it seems reasonable to replace the seals and update the B2 piston, my tranny works so well I'm reluctant to fix it until it is broken. And it appears I could get to this later if I wanted to. Your confirmation is enough for me to just go forward and get this thing back in. Thanks.

borland

He had to remove the B2 piston in order to inspect the clutch packs. Without removing the B2, he could only inspect the clutch pack in the front by the main pump and converter.

Bill Ball

Well, that's one for it not being normal to be able to move the cover. This is B2, right?

Bill Ball

It sure looked untouched (the area was covered with very old grime until I cleaned it). I don't think he got back to the rear clutch packs - just K1.

PorKen

Interesting. Your '89 diff case already has the '90 PSD boss.

If you talk to your trans guy again, could you ask if there is a kit/parts to delete the secondary pump? (Some later Mercs do not have it.)

borland

The '89 instrument cluster also has the bulb slot and stensil for PSD.

The delete is possible using all mercedes parts. Even if you never tow, why pay for it?

Bill Ball

Well, another oddity...looking over the bill, the part number for the B3 piston is for MY88, not 89. 89 uses different springs with the B3 piston. I don't suppose anyone knows if this is a problem. The rebuilder is a smart guy, knew it was an 89, and the price he charged me for the part is consistent with 89 rather than the more expensive 88 part (according to PET). I need to call him again, but I think (hope) this may be a billing error (ordered and charged me for the correct part, grabbed the wrong PN when writing up the bill - I hope).

borland

We looked at your B3 piston on the other thread. Nothing wrong with it then.

Why would it need anything other than new piston seals? Did you get the old parts back?

Bill Ball

There is a locator pin on the back of the B3 piston that was broken. I saw it. Not sure it matters, but I OK'd replacing it. See pic below - not our tranny, only one I could find that shows the pin. He had my used parts in a box, but I forgot it, and they got tossed.

I just talked to the rebuilder again. He said the B3 he installed is identical to the one he removed - the PN is cast into it. Mine is a fairly early 89. Also, he reassured me there is no reason to suspect a problem with B2 piston just because I can move the cover. He did not go into that area nor did he remove the B2 band or reactor.