B2 Brake band replacement / adjustment.
 

I've got the classic B2 brake band / shift valve problem - slipping in 1st / 2nd gears. Is this a DIY job, or am I best to ship it to a tranny specialist? Any one have any decent links to threads, or relevent WSM section (I have Pdf manuals) that I can refer to? (I've already serviced the tranny and checked fluid levels to no avail, so can only assume the brake band is shot). Car is still driveable, albeit not exactly quick of the mark any more! I have a reasonable stock of tools, but can only raise car about 6" from floor, so access is limited.

Thanks

One of the bands is adjustable from the outside of the transmission. Can't remember if it's the B2 or not but one of them is on the outside. You'll have to cut a notch into it, then you can hold/turn it when the locking nut is released. Do a seach on her and you'l find more info.

Make sure that the b2 piston is intact. Mine went out a few years ago and the trans would slip in the lower gears.

If the piston is ok, you may want to see which version you have because you'll probably wind up breaking it sometime in the future. MB has re-designed that part at least 3 times.

Also, the b2 is adjusted by replacing the pin between the piston and the band. Think of the pin like if it was a connecting rod inside the transmission. The pin is a solid piece that's milled in the center. Sort of looks like this O====O

MB offers multiple lengths. There's a procedure on how to check for the proper length.

BTW, my information is based on an 87...I'm not sure how this differs with the other models.

Good luck...

Regards,
Roger

Checked WSM regarding fault finding for your problem:

Condition:
Transmission slips when moving off in 1st or 2nd gear. or moving off not possible in forward gears. Reverse still good.

Cause/Correction:
1. Service shift valve B2, replacing shift valve housing if necessary.
2. Replace brake band B2 piston.
3. Adjust brake band B2 by installing a longer thrust pin.
Replace brake band in case of excessive wear or brokent brake band.

This is well within capabilites of a competent DIYer

Roger's comments +1

Measurement of B2 brake band clearance requires you to remove pan, valve body and then you can check band and clutch for wear or brakage and B2 clearance to determing what pin to fit.

You can remove B2 piston relatively easily, inspect B2 piston or renew to upgrade type (purchase from MB dealer as usually much cheaper then Porsche) an insert a longer pin, but this is a bit of 'hit or miss' procedure.

Web site for Transtec : http://www.transtec.com/tech_info_by_trans.htm
and click on Down Load Technical Supplements and choose “Mercedes 722.3 and 7224” and you should be able to download a 12 page document relating to the MB or Porsche A18/16 auto box which is a MB 722.3 transmission.

B2 Piston Failure in MB 722.xxx automatic transmission at http://business.baylor.edu/Richard_E...s/b2piston.htm

If you have Jim Moorehouse Technical CD it has a copy of the Porsche’s 928S Automatic Transmission A28, Description of Operations ( WKD 490 521) is included.

Try google search for Mercedes Benz 722.3 Automatic Transmission Repair as there is plenty of information there.

MB Technical Bulleting No 268 is here for slippage between 2nd and 3rd gears: http://autorepair.about.com/library/faqs/bl160h.htm

K1 Piston: http://www.benzworld.org/forums/w201...t-install.html

Refer to my previous post for B2 piston replacement procedure with pictures. This is a long PDF document in three parts.

Tails 1990 928 S4 auto

Thanks Tails for all the info!

Any chance of a link?

Bert,
Not sure how to do the link stuff, but if you check my previous posts there four parts posted on the 26th January 2006 relating to the B2 Piston change and an extra post relating to the modified AT pan gasket on the same date.

Tails 1990 928 S4 Auto

Thanks Tails, found it!

https://rennlist.com/forums/928-forum/250248-automatic-transmission-b2-piston-replacement.html

Tails:

A couple of the links above are dead...

B2 Piston Failure in MB 722.xxx automatic transmission at http://business.baylor.edu/Richard_E...s/b2piston.htm

Web site for Transtec : http://www.transtec.com/tech_info_by_trans.htm
and click on Down Load Technical Supplements and choose “Mercedes 722.3 and 7224” and you should be able to download a 12 page document relating to the MB or Porsche A18/16 auto box which is a MB 722.3 transmission.

The "Download Transmission Technical Supplements" link is dead...maybe they will fix that.

Thanks for the others. I have archived them.

Do I have to drop the box to change brake band B2?