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Old 04-26-2005, 11:58 PM
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Join Date: Mar 2005
Posts: 7
Transmission Vaccum modulator

Hi, I have a slow shifting transmission on my 300E, that has being doing this for the past 30K miles. I was told that there is probably nothing whrong with the tranny but the vaccum modulator is shot. I replaced the old vaccum hose (which was leaking) and the shifting improved but not to normal. I have bought a vaccum modulator from MB for $36.00 and want to install IT, but i heared that it is necessary to adjust / tune the modulator after replacement, and I have no Idea on how to do it and nobody that I know seems to be experienced on this. How do you go about replacing and adjusting the modulator???
1987 MB 300E w124

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Old 04-27-2005, 09:50 PM
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Join Date: Mar 2004
Location: new york/orange county
Posts: 639
The old vacuum hose, which was leaking should have made the shifts harder. If by soft shifts you Mean early, and then adjust the Bowden cable.

The modulator for your car should be black in color for a 722.320 transmission.

You may have to remove the transmission cross member to access he modulator. First remove the two Allen bolts from the modulator retainer and then carefully pry it from the case. Remove the plastic modulator pin and check it for cracks if it, the part # is 126 272 20 74 it comes with a new valve.

After you installed the new modulator leave the modulator vacuum line off; install a 100 PSI gauge to the pressure tap located under the modulator; you are setting the modulator pressure with “0” vacuum. With the rear wheels off the ground start the car and select “D”, bring the speed to 31MPH and adjust the modulator the 57 LBS if nesaseeary by turning the “T” handle located under the rubber cap on the modulator. CCW= lower CC = rise.

If you bought the new style modulator and pin, it looks different then the original one, you have to buy an extra cap that covers the adjusting “T” handle. Once you remove the cap you have to replace it with a new one. The adjusting procedures are the same as above. Don’t forget to connect the vacuum line when you are done.

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