84 300sd Transmission Issue - PeachParts Mercedes-Benz Forum

popimor · #1 06-11-2009, 01:11 PM

I have an 84 300sd with 240k miles which I have owned for 3 years or so. In the morning (regardless of temperature outside) when I drive the car and the car gets up to 4th gear and then I come to a stop there is a clunk that can be heard and felt when the car downshifts just before I come to a stop. This does not happen if I put the shifter in 3rd and don't allow the car to shift into 4th. After the car warms up a bit (5 min. or so) I no longer experience the same problem.

Other info:
- vacuum modulator needs to be replaced (upshifts are pretty harsh).
- transmission fluid looks and smells fine and is at the appropriate level
- may need new motor and transmission mounts, but none are broken.
- it takes a second or two for the car to go into reverse or drive when selected.
- I have had the car not want to shift out of 1st before. By tugging on the bowden cable a few times this issue would go away instantly. Since lubricating the cable I have not had the same problem. COuld I still have issues with the cable that may cause the new problem?

Am i just dealing with a warn out transmission or is there a possible fix?
Could this be associated with the differential?
Could replacing the vacuum modulator fix/lessen my problem

Thank you. I really appreciate the help and knowledge on this forum.

oldsinner111 · #2 06-11-2009, 02:19 PM

Sounds like you have vac problems.The little valves under the plastic rocker box tend to break with age(hard shifting,Clunk when slowing down.The EGR valve could leak and thermo vac valve.No one carries the little S shaped hoses for the 3/2 valves.
My case I got rid of thoose (legal state).Then sent one vac line to a 3 way conector one going to transmission,And the plastic white valve on the IP.The bottom (white valve) port vent to a vac line to cabin (bleed off,no vac on it).As for shifting replace bushings on shifter and trans.