I'm trying to adjust the vacumm to get the tranny shifting smoother. Is this the dial I need to adjust?

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You are looking for teh modulator mounted on the side of the trans housing. Approx 3" x 4" thing with a rubber cap on it you remove. Iside is a key you pull out to unlock and then turn to increase or decrease pressure.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

ELR is the engine idle speed control.

Is this done on the car or does the modulator have to be removed?

Can this adjustment be used to crank up the vacuum at the transmission end to make up for the blue pod-from-space on the drivers side fender not sending quite enough vacuum to it?

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Well you need to check a vacuum gauge to see if the vacuum getting to the transmission is what you think it should be. Check at the line feeding the transmission modulator. Depending on throttle position the vacuum will vary from high to low.

On my 92 300TDt OM603 there is a pie sliced shaped modulator on the side of the IP which modulates vacuum to the transmission modulator on the basis of throttle position. part number 123 300 10 33, revised 140 300 08 33.

It provides high vacuum to the transmission when under light acceleration, and low/no vacuum to the transmission when under high acceleration. It does this by moderating the amount of vacuum to the transmission versus how much air is drawn from the vent line.

If the transmission flares into gears under full acceleration then it's not working properly If the transmission thumps into gears under light acceleration, then it's not working properly.

Assuming of course the transmission is working properly in the first place, and the modulator on the transmission that is modulating fluid pressure is adjusted correctly.

So before adjust the modulator on the transmission you should confirm the vacuum supply is working as expected.