In a 4 speed 85 auto (Euro) during a 3-4 upshift is
a brake band applied with a servo or is it a clutch pack that gets
energised?

Reason is mine has a bad flare (revs rise between 3rd & 4th) and I been given various advice from "a can of Lucas oil additve will fix it" to "she's knackered and will need a rebuild" & " will only need the servo seals done".

Cheers,

Robbie A.

 

Check the transmission fluid level and condition. Does the fluid smell burnt if so the clutches in the drums are burnt? How about the other gears any slip or flair shifts. Any delay going into D or R


The K1, front clutch drum and K2, rear clutch drum are on for 4th gear. Any leak (sealing rings, piston seals) in the drums will cause a slip or flair shift. Low working pressure will also cause a slip/ flair shift, but then you would have a shift problem with all or another gear.

You can raise the working pressure by turning the T handle in the modulator CW two turns to mask the internal leak.

It has been my experience that with a bad 3rd to 4th up shift it is an internal leak.

 

Thanks Steve,

Is the "WORKING PRESSURE" (I guess this is line pressure) adjustment internal or external.

Robbie

 

The vacuum modulator controls working pressure; it’s located on the driver’s side in the middle of the transmission. You will find the “T” handle under the black rubber cap on the modulator, just pry it off. To adjust you have to pull the handle out a little and turn CW. If the adjustment does not make the 3 - 4 shift better you need a rebuild.

 

Steve,
What is the implication of your other question point "Any delay going into D or R " ?

 

A delay going into R is typically a B3 issue, from the cars I've driven.

I've never driven a car with a bad clutch pack. K2 pulls in for 4th. Lucas will raise the internal pressure, much like increasing the setting on the vacuum modulator controller.

From a previous posting:

Simplified....
1st* - B2; 2nd*- B1&B2; 3rd- B2, K1; 4th K1-K2; Reverse B3 and K2.

 

For diagnosing two applying components. In drive to diagnose the B2 piston seals and in reverse for the K2 drum seals

For Drive:
The feed oil that applies and releases the B2 piston is used to apply the K1 and K2 drums; 4th gear, a leaking B2 seal will cause and has been known to cause a 3rd to 4th flared up shift. If he had said yes, I have a delay into drive I would have recommended changing the B2 seals first.

For Reverse: K2 and B3

With a delay into reverse and a known 3rd to 4th flared up shift, I am more inclined to believe that the K2 drum seals are leaking, instead of a B3 clutch problem, the other applying component for reverse.

I could have isolated the K1 drum but while I was typing I was convinced the transmission needs rebuilding, I was too lazy type the other question.

 

I would say that a delay into reverse is the reverse clutches. These wear all the time the car is in forward motion. Mercedes revised the material and it is now nitrided, hence the different color of the clutch material. They are normally shot after 100k miles.

Cheers Greg

 

Thanks for the responses - it helps to understand the 'symptoms to component' relationships ....

 

I have been trying to figure this out; I just can’t see how adding 24oz of an oil modifier (Lucas) can raise a transmission line/ working pressure.