I own a Mercedes 300 SDL. Recently, it began to shift at a much higher RPM than normal. Normally, it shifts up at 2500 rpm or so from 1st to 2nd gear; now, it tends to slip shifting from 1st gear to 2nd gear. At 30% throttle, it won't upshift into 2nd gear until ~4,500 rpm. When 2nd gear is finally engaged in the transmission, there is a noticable but brief surge of acceleration, then more slipping if the accelerator is pressed too hard.

A transmission shop took the transmission out of the car(under warranty), ran a few tests on it, and could not find any errors(they may be lying about that). Any indication as to what could be the cause of the problem?

If the transmission is not an issue, perhaps this is vacuum related?

 

Check vacuum supply at the modulator valve on the left side of the transmission. If there is insufficient vacuum, it could create this issue.

 

Hello,

I have a mercedes 1987 300 SDL - I am currently experiencing the same problem listed above. My car won't upshift until 3500 RPM.

We checked the vacuum at the module & it has good vacuum.

Does anyone have any further suggestions? What exactly should I be checking the vacuum module for?

Thank You