totdoc67

Hey guys,
New member on Rennlist and this is the first post I've done. I have a 1989 928 S4 that has just completed a trans rebuild. The problem is that the overdrive does not function. The transmission guy thinks I need to replace the valve body...is there anything else that I should be thinking of?
Really appreciate any help

Randy V

Well done, sir - got a first name, and location?

Often the problem is proper setup of the associated control cables.

Here's a good overview of the setup procedure:

https://rennlist.com/forums/928-foru...l#post10498854

And, welcome!

FredR

That is a bit concerning if your transmission specialist tells you the "Overdrive" is not working. More so when the unit has been "rebuilt" and still needs a valve body- maybe I need my second cup of coffee here.

Unless I have misssed something for the last 18 years never heard of a 928 [aka Mercedes Benz] transmission with an overdrive on it but...?

Perhaps you can clarify what exactly you are experiencing symptom wise- i.e. what works and what is perceived not to work.

Welcome to the list- I am sure you will get some great support.

totdoc67

Thanks guys for the help. The car with the rebuilt transmission shifts well, but when you get up to highway speeds (70-75 mph) the engine sounds like it is maintaining a lower gear and the rpm's are running in the 4000+ range. Otherwise shifting is appropriate.

Thanks again for the advice.

Sri
Chicago, IL

The Forgotten On

Most likely it is the adjustment of cables as posted above. My 89 had a similar issue. Adjusting them per the WSM fixed it.

FredR

Sounds as though the box is not dropping into 4th gear. First thing I would check is whether the kick down cable has been installed way too tight [it is the cable that is outboard and a bit lower on the throttle quadrant] and should be held in place by a small spring clip.

When the ball cup is disengaged and the cable pulled tightish the socket should be a little to the left of the ball. If this is not the case and the socket is to the right of the ball loosen the cable until it is about aligned and try that to see if it helps at all.

If it does not solve the issue then you may have deeper problems.

Presumably you are happy that whoever filled the tranny with ATF filled it correctly - that can also be a sensitive matter.

GregBBRD

Interesting thst anyone would "rebuild" a transmission and not disassemble, clean, and rebuild the valve body the valve body. The valve body is the most important part of the job.

That's like doing an engine rebuild and not doing the heads.....