W124 E300 D Slip in first gear- advice needed.

[jon2h]

Hi. I'm new on here.

I've just signed up for advice after having a problem with my '94 E300 D slipping in 1st.

For some time when pulling off in 1st I have felt a clunk like something is bedding in. This later developed into a judder, which I assumed was worn tripod joints, however, this has recently developed into a bad slip in first, and a maybe slight slip in second. Prior to the slip, everything worked fine- no flares or anything.

I've checked the ATF which seemed OK, and pulled the tube off the VCV, which made the shifts really hard but did not affect the slipping, so I don't think it's modulator related either.

The behaviour is the same in D,2,3. R is fine.

Having read around, it looks like it's B2 related, but what I don't get is why it would only slip in 1st when B2 is needed for 2nd and 3rd as well:

Selector Lever Position
Elements In Use (1)
"D"
1st Gear .................... B-2 Brake & One-Way Clutch
2nd Gear ......................... B-1 Brake & B-2 Brake
3rd Gear ........................ B-2 Brake & K-1 Clutch
4th Gear ....................... K-1 Clutch & K-2 Clutch
5th Gear ...... K-1 Clutch, K-2 Clutch & Overdrive Brake
"3"
1st Gear .................... B-2 Brake & One-Way Clutch
2nd Gear ......................... B-1 Brake & B-2 Brake
3rd Gear ........................ B-2 Brake & K-1 Clutch
"2"
1st Gear ... B-2 Brake, (2) K-2 Clutch & One-Way Clutch,
2nd Gear ......................... B-1 Brake & B-2 Brake
"R" ........... B-3 Brake, (2) K-2 Clutch & One-Way Clutch
"N" & "P" .................. All Clutches & Bands Released
(1) - Overdrive clutch and 2nd one-way clutch are also in
effect on 722.5 series transmissions.
(2) - Applied but not effective. K-2 clutch provides engine
braking in Reverse and manual low.

Are there any other common causes?

If it is B2, what are the likely parts to have failed (piston seals etc.), and can you get at them with the transmission in the car?

Cheers for any help

Jon

 

[Siben]

"Having read around, it looks like it's B2 related, but what I don't get is why it would only slip in 1st when B2 is needed for 2nd and 3rd as well:"

In second gear, the B1 band is applied as well. In third gear, the K1 clutch s applied as well. Only in first gear, the B2 band acts alone as a braking force. Apart from the one way clutch.

The reason for this slippage is worn cylinder around the B2 piston. The large teflon seal around the B2 piston isn´t quite leak tight.. so to speak.
Solution: Take out the B2 piston and grind a 30° chamfer on the piston edge under the teflon seal on the cover side. ( Outside )
This gives the oil easier way underneath the teflon ring and expands it.
This was actually a TSB from Mercedes at some point..

Cheers,
Siben.