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Old 08-23-2002, 12:00 PM
surfblau's Avatar
neue Dieseler
 
Join Date: Feb 2002
Location: san francisco - immer kalt, immer windig, I want to move
Posts: 382
Do I have a bad transmission modulator?

(I have been posting on another thread, but it is getting a little long).

Symptoms- moderately hard to neck breaking shifts at all speeds, at all temps, in a 300SDL 87 - 126 with OM603.

I have been monitoring the vacuum line pressure on the line that goes to the transmission modulator and have observed the following:
- idle parked is 14psi
- idle at highway speed (on a big downhill) is "usually" 14psi
- full throttle is around 5 or less psi
- pressure varies proportional to pedal pressure from 14 to +/- 5 psi

All that seems fine. Here is the problem. 50% of the time when on city streets, when I accelerate and get the vacuum below 10psi, the pressure will not return, and often leaks off and hovers around 4psi. I get terrible shifts at this point.

However, if I pump the mightly vac to get the vacuum back to 10psi or so, the needle will usually recover its freedom of motion and will "work like it should" - that is, varying between 14 and 4 psi. The shifts at this point are absolutely perfect.

There are no leaks in my vacuum lines or connectors.

The modulator will hold a 15psi vacuum applied directly to it.

Does it sound like my modulator is toast?

Any help appreciated.

thanks
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