PC-85-928S

Has anyone ever changed the B2 Brake Band on a A28, 928, automatic transmission?
My 1985 928S, auto has been slipping off the line.
I read some post on this site about the B2 brake band, and how it could be inspected and repaired, with the transmission in the car.

is there a kit for this part?

GregBBRD

Me thinks they are talking about the B2 brake band operating piston being able to be replaced in the car....you could change the brake band in the car...but you'd need to remove the car to do it.

Landseer

There is a b2 piston and sleeve that can be replaced in situ. (I've done it and taken pics)
Longer actuators can be installed. I've bought a set of increasing length ones, but ended up putting original back in. There is a procedure for measuring, simply, the actuator length needed.
Its not possible to see the condition of the band without removing trans.

Replacing Friction surface I think requires pulling trans.
I have a spare, but suggest if you go to the trouble that you buy new.
MB parts counter and other trans supply sources have them.

PC-85-928S

Yes
Sorry
I see it is the brake band piston assembly
Does fluid leak out if this is removed while trans is in car?

Landseer

Drain, remove pan, remove valve body ( I think 2 pieces ) let it drip a while.

It'll drip a bit on your face but not much during the work.

Check archives here: "Tails" did excellent work that provided my base. I also put a few picture threads together w/ part nos.

UncleMaz

+1 on Tails.

Tails was kind enough to send me all of his work documents when I did this on my C Class Mercedes trans a few years ago. I can send you all of the documents along with the trans manuals if you PM me your email address.

PC-85-928S

Yes
Great post and pics
Need source for b2 brake band piston for 1985 28.04 trans
M/B 722.3

GregBBRD

Actually, the brake band, the operating piston, and the spring loaded shock absorber on the other side have all been superceeded to different parts. The brake band material was changed, which required a different "shock absorber". You can update the piston, without changing the band or shock absorber.

UncleMaz

From the MB 722.xxx trans manual:

Transmission Slips When Starting Off In 1st Or 2nd (Reverse
Is Okay)
Band B-2 shift valve sticking. Band B-2 piston worn or
damaged. Band B-2 adjusted incorrectly or worn or damaged. Adjust
brake band B-2 by installing a longer thrust pin (if necessary). If
transmission operates properly with selector lever in "2", but not in
"3" or "D" position, one-way clutch may be slipping.

Landseer

Some random shots that might help

(Archives of seem to be unsearchable or purged.)

UncleMaz

Emails sent.

UncleMaz

Landseer, I have all of it plus. Just tell me where to post it.

Tails

You have received all the advice required to do the B2 Piston and you can measure the distance as Chris has explained with the transmission still in the car and you can fit the correct length pin.

If the bands are worn then you will probably note residue in the pan when you remove it, however, if one of the three pins can take up the slack to specification then OK, no need to fully remove the transmission.

I would also fit a new upgraded B2 Piston as shown in Chris' photographs, as they are prone to failure. If they do fail you will loose all forward gears, but retain reverse.

Suggest that you buy your parts from Mercedes Benz as you will probably find that the parts are cheaper than at an OPC, as the 722.3 auto boxes are make by MB. Make sure you change the filter etc, a kit is available and also ensure that you fit the upgraded pan gasket. The part number ends in "11", so don't fit the pan gasket if it ends in "10".

When you have it all back together then you need to adjust the modulating valve to aquire the best gear change you require. I would suggest that you take the car to a MB auto box specalist shop to undertake the adjustment unless you are a good DIYer and you have the WSMs, obtain a nipple that fits in the side of the box just forward of the modulating valve and fit a pressure gauge to the nipple and you can adjust the modulating pressure at an idle speed around 1500rpm whilst on jack stands in "D".

Tails 1990 928S4 Auto

Landseer

B2 Piston 107 270 00 32 also supercedes to 107 270 04 32 $120.00

B2 Seal Ring 005 997 70 48 $1.50

Brake Band Bushing 126 277 08 50 $5.78

Transmission Seal for B2 Servo 006 997 73 47 $3.52





Here's the part numbers for the dogbone actuators (various lengths) and what I paid for what I bought.
Not sure what the effect will be of the longer pins, but I think it will take up slack when the band is worn. *don't bother with the much longer pins, only the first few are relevant.

A 126 277 71 75 47.2mm Pin
A 126 277 72 75 48.0mm Pin
A 126 277 73 75 48.8mm Pin $7.56
A 126 277 74 75 49.6mm Pin $7.56
A 126 277 91 75 51.0mm Pin $5.29
A 126 277 92 75 52.5mm Pin $5.29

In the Mercedes parts system, the lady typed in the good part number 107 270 04 32 for the B2 Piston so she could see a parts explosion and then select the nearby part number for the pin. Here are some of the codes that printed on the printout she gave me:

Market: North America
Catalog: 67W
Group: 27 - 722.3 Automatic MB Transmission
Subgroup: 060 Brake Band, Brake Band Piston, Transmission Overload Protector Switch



Here is a link to the original post I made for doing the piston swap, which in-turn references Tails' much earlier link and leads to his writeups. Black 928 has also been deep into this so his emails might help!

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

simos

Found this old thread some time ago. Good information of howto check and adjust modulator pressure. Actually my box was shifting too early and found, that pressure was close 5bar. Now the sifting points are quite right


https://rennlist.com/forums/928-foru...-pressure.html