92 300 D 2.5 tranny ? - PeachParts Mercedes-Benz Forum

04 Diesel · #1 04-21-2014, 04:12 PM

My 92 300D 2.5 turbo has over 300,000 miles and tranny has been slipping for a while now, but lately it is slipping more. It would just slip when in reverse, sometimes from 1 to 2 shifts. Now it seams to be all that but more in forward now. I know how to firm up the shifts by turning the vacuum control valve on the tranny, I turned it two notches clockwise, I will see what that does. Fluid is full, changed fluid and filter not too long ago. Just to be sure, you check tranny fluid with car is warm and running and in park? I cant remember if you check in park or neutral.

Zulfiqar · #2 04-21-2014, 05:08 PM

park or neutral does not matter. what matters is temperature. To get it upto temperature you may need to drive it for about 20 minutes. The cold reading on the stick is useless. In your car the dead cold reading is actually where the dipstick pointer curves upwards again.

jt20 · #3 04-21-2014, 05:26 PM

You may get the results you are looking for by adjusting the modulator on the trans. Considering that you are 'slipping' in reverse is a sign that it may be a good idea.

However, I think its best to get the vacuum system working properly before adjust the modulator though.

adjust the vacuum control valve to spec (the write up for the shift kit is a good source)

test vac system for leaks

adjust the vacuum amplifier by feel (there is an adjustment key under a friction fit cap)

If you cant get firm shifts by those, then adjust the modulator.

Of course, the history of that modulator and trans is certainly up for scrutiny by now, and adjustments to the modulator may be corrective.

---
Trans should be at operating temp.

Zulfiqar · #4 04-21-2014, 05:37 PM

You can also try using some Lubegard red, it helps to keep the transmission working sweet. I added some to my W124 and its now quicker to shift into reverse. (not GM quick - but quicker by MB standards)