UncleMaz

944 owner. Don't hurt me. My Mercedes 1994 C280 Auto Transmission recently left me stranded. It was serviced the day before (overfilled) and while climbing a canyon road, all forward gears failed to work. Reverse works fine. I have a 722.4XX transmission in my car now. Steve Cattaneo informs me that the transmissions are similar. I have sourced a 722.3 transmission but would like to give this one the college try and see if I can get it working. I found these resources for servicing the B2 piston http://articles.mbz.org/transmission/b2/why/
http://articles.mbz.org/transmission/b2/repair/ but would love more information on things I can do to get this sucker working again. I also just bought a used 722.4 B2 piston on evil bay for 30 bucks. I am a DIY'er who has swapped 944 transaxles but have little or no experience wrenching on automatics. Really, I have never cracked a transmission of any kind. If the b2 piston replacement does not work, how hard is it for a DIY to access and repair that? Also, where does one source parts? Any help is greatly appreciated. Thank you very much. Michael.

Mrmerlin

I think you should go back and ask Steve C he will guide you through the process of this repair, He is the Trans Guru MASTER !!

Tony

X2.. he IS the man when it comes to these tranny's. Did you try draining the fluid back to the correct level?

Tails

Michael,

B-2 pistons are quite easy to change by a competent DIYer without removing the auto box from the car, all you need is ramps and jackstands.

Please send me your e-mail address and I will send you information to help you.

Tails 1990 928S4 Auto

SeanR

The B-2 valve is held in by a large C-clip on the passenger side of the transmission. If you remove that clip the B2 will come out real easy. You just need to compress the B2 to relieve pressure on the c-clip. (I did this by hand, took several tries, but can be done)

Now the fun part begins. Drain everything and get a new pan gasket and filter. Check the pan for parts of the B2. When it goes it will go in many pieces and if you get lucky they will be contained in the B2 housing. The most recent one I replaced was in about 10 pieces. When you get the new B2 you will look at it and wonder how in the hell all of those springs/spacers fit in that small contraption.

If there are no extra parts floating around in the pan you can just lube up another B2 and put it in. Refill your transmission per the manual, and go for a drive.

Mrmerlin

I guess this goes without saying but there is an updated B2 module make sure you get this one , and i dont remember the updated part # sorry

UncleMaz

Thank you so much. PM sent.

Steve has been really helpful. I am not worthy.

928 people are much more friendly than............

UncleMaz

Thank you!

ROG100

107 270 04 32 latest superceded number for the B2 valve. I sell for $130.

UncleMaz

Is this something I should replace irrespective of the condition of the piston? Thanks. Michael

Steve Cattaneo

Your C280 has a 722.4 transmission, the 722.3 you found (Bigger transmission) will not bolt up to a 2.8 engine. If you need a transmission it must be a 722.4. Check the B2 piston, if you find no broken pieces the B2 band is broken, common with 722.4 Transmissions.

UncleMaz

The information provided should give me a good start. Thanks Steve. Per your suggestions: Next weekend, my plan is to check the for metal in the pan, pull the cover off of the b2 piston and replace if necessary. Do I replace the B2 Valve while I am under the car if the piston is bad? If I find metal shavings should I move on to another tranny or is that another path entirely. Finally, if I find no metal shavings and an intact b2 piston and have to drop the transmission to replace b2 band parts, is this something I can do? If all lines up, I feel like I can do this. Thanks 928'ers, thanks Steve, thank you Rennlist. I will report back next weekend after I am under the car if not sooner. Michael

UncleMaz

Hello. Well, I finally had time to get under the car today to pull the B2 Piston. I was able to push in the cover and get the c-clip off (trans mount is disconnected and tranny is pushed to one side). Now, I cannot seem to get the cover off. It no longer pushes in and I can spin it, but I cannot seem to get it off. Any suggestions as to tool or method to get it off. Also, I can see the red o-ring and it doesn't seem to spring back out/push back in anymore. Separately, once I get the piston out and drop the pan, I will take some pics for thoughts on diagnosis. Your help is greatly appreciated. Michael

SeanR

Tap the cover lightly all the way around it. It will get cockeyed at times. When the cover does come off, there might be many different parts in there, so fish around with your fingers.

UncleMaz

Sean, thanks for the reply. I will give that a whirl. I still don't have that cover off. In the meantime, this was in my pan when I took it off - the metal plunger thing that appears to be the one at the end of the piston. I am not sure if it came off when I was removing the c-clip or was in there when the tranny gave - probably the former as I pushed on it pretty hard with a screw driver when I was removing the clip.