Spun

After I got my Cab running, I noticed a little slip in the auto tranny. I have had the tranny flushed at known good 928 Mech in tucson, but I still have slip between 1st and 2nd more than I like.

My other 89 does not shift like this. It is solid like a tank.

It happens is at lower RPMs, the tranny has a pretty good slip (about 1 seconds) and then its fine.

I have not noticed this between 2-3, etc... but plan to play a little more before Sharktoberfest...

I will also have it at Sharktoberfest for driving for additional diagnosis...

Is there adjustments i can make?

I have not found anything that stands out at this time...

Thank you in advance

ammonman

If the 4 speed slips when moving off in 1st or 2nd gear or won't move at all in forward gears but reverse is ok then there is an issue with the B2 control valve in the valve body, the B2 Piston, or the B2 band. Might be time for the B2 Piston update or a new B2 Piston lip seal, if it hasn't already been done. If all you do is the B2 piston it can be done with the trans in the car. According to Dr. Brown, the B2 update includes a new style B2 Reaction element. This requires at minimum the valve body and lower cover be dropped. I haven't actually done the job, but after a lot of reading I THINK the B2 Reaction element can be changed with the B2 band still installed. Someone with more knowledge will be along soon to confirm or refute.

Mike

Landseer

What is the B2 reaction element?

Is it the dogbone looking piece, available in multiple lengths, for actuation of the B2 friction?

If so, I've done it in situ.

I don't have enough experience to be able to say that is your problem.
Here are pics if you decide to attempt replacement of B2, sleeve and possibly dogbone.

GregBBRD

The "updated piston" does call for a new "reaction valve" and a new style brake band. I'm not sure I'd bother with either one, if I had a piston that failed and I wasn't doing a complete rebuilt. There is some thought that the "new" piston may need the updated shock sbsorber and the different brake band, because it "hits" harder. (I have seen brake bands break, after the piston gets changed.)

BTW...the '89 model does have a 1/2 way updated B2 piston....which is pretty durable. I've still got brand new old stock on those original pistons.

For the OP. Make sure that you have vacuum to the modulator and the modulator does not leak. That little rubber "black" cap on the modulator will crack, from age, and you can loose most of the vacuum, right there. Make sure that the "kickdown cable" is hooked up and properly adjusted. Make sure that the "return spring" for the kickdown rod is present, inside the transmission.

Any of these things can make the transmission shift poorly.

ammonman

The B2 Reaction element is the part mounted to the other side of the transmission case that the other end of the B2 band connects to. I guess you could call it the "fixed" end of the B2 band as the B2 Piston is on the "movable" end of the band. PET calls it a "valve" and is shown as item #12 in the pic below.

Landseer

That piece, and band replacement, I'm pretty sure require trans removal.

Spun

Hmmm... 1st does not slip... it does slip the most between 1st and 2nd with a little slip at 3rd... Reverse is solid and 3rd to 4th seeps solid.

The more I am on it the less slip I get. If I am just tooling along then it will slip the most.

Landseer

Precision Motorwerks is the master of these transmissions; first choice would of course be taking it there. I would if I could.

Spun

I had thought about that... I will be at sharktoberfest, but I am not sure when we will arive. I may give him a call and check to see ...

GregBBRD

I call it a "shock absorber", for lack of something better, until now.

I do like "reaction" element", if I can remember that!

GregBBRD

These transmissions don't "normally" start in 1st gear. Most people that "start" them in 1st gear are manually shifting them. Does this slip occur then, or does it only happen with an "automatic" shift into 2nd gear? If that is the case, how are you getting it to "start" in 1st?

Landseer

There are different length actuator bars available to compensate for some band wear.
Seems like a patch though, as by the time its needed the band would probably have degraded in other ways.

ammonman

The Mercedes manual calls that part a "Pressure Body" while the WSM calls it a "Pressure Unit". Not sure where I came up with "Reaction Valve" but after all the reading I did to complete my transmission work I know somebody else coined the term and it stuck with me.

Mike

GregBBRD

Amazingly enough, it's virtually impossible to know what length you need, until you actually put the thing together. Even the pistons vary way more than you'd think was possible, for a production part.

And on top of that, frequently, none of the rods that are offered are "long" enough for the updated brake band and the updated piston. I sometimes have to make custom length rods.....which is just....wrong.

GregBBRD

I like it!