1981 300CD 722.118 trans not shifting - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 10-01-2012, 05:21 PM

I got this 1981 CD a couple years ago. I was told the trans was just rebuilt. It was used by my niece for the past 2 years to go to college. I got the car back a couple weeks ago and the trans started shifting weird. I found the modulator to be bad, so I replaced it. It then would not upshift until it was warm. The next day, it would not shift into second unless it was revved to redline, and then it would shift hard enough to get 2nd gear scratch. I took it to my local trans shop, and they checked everything they could without removing the trans. I removed the trans and brought it to them. Upon disassembly, they noticed that everything inside was perfect. No worn parts, governor working as it should, and no clogs in the valve body. The only thing they thought might be the problem is the seals inside the trans. They said it was probably built with a Braco? kit, and not genuine Mercedes Benz. They suspect the seals had shrunk, causing it to loose pressure. Has anyone ever heard of such a thing? They suggested a factory seal kit ($306) in order to insure it will last. Phil has the Meyle kit for less than $200, but I am not sure if the Meyle kit is better than the Braco. Anyone have an opinion or suggestion as to what I should do? Thanks in advance, Rich

carnut · #2 10-01-2012, 07:57 PM

I think the throttle pivot vacuum switches bolted to the valve cover are broken allowing delayed vacuum to the modulator. Does it have a large black plastic cover, covering the throttle linkage at the toip center of the valve cover? There is also a metal "T" inside the modulator that can be adjusted to tailor vacuum signals. I dont think its an internal trans problem. I think removing it was not needed. I assume you read the 7th post down from yours?

kerry · #3 10-01-2012, 09:22 PM

Did you check for a sticking kickdown switch before removing the transmission?

ROLLGUY · #4 10-02-2012, 12:08 AM

Quote:

Originally Posted by carnut

I think the throttle pivot vacuum switches bolted to the valve cover are broken allowing delayed vacuum to the modulator. Does it have a large black plastic cover, covering the throttle linkage at the toip center of the valve cover? There is also a metal "T" inside the modulator that can be adjusted to tailor vacuum signals. I dont think its an internal trans problem. I think removing it was not needed. I assume you read the 7th post down from yours?

1981 is vacuum only, no control rod or cable. I checked the VCV before replacing the modulator, it checked out fine. The trans acted the same before and after replacing the modulator. I tried adjusting the "T", and it made no difference.

ROLLGUY · #5 10-02-2012, 12:10 AM

Quote:

Originally Posted by kerry

Did you check for a sticking kickdown switch before removing the transmission?

I did not, but I will advise the trans shop. However, they said they checked everything that could be checked before telling me the trans needed to come out.

Stretch · #6 10-02-2012, 03:17 AM

The theory of magic shrinking non MB seals can be tested - make some pressure measurements.

In fact the fastest way (from the experience of others) seems to be to make some pressure measurements and check against the data in the FSM / stuff on WIS. If you need this you know where to come right?

I'd also be checking the vacuum system and that pesky 3/2 valve.