OK, accept the fact that I am not going to explain this very well and ask me some questions. The car normally shift pretty well at about 2800 RPM's, but every once in a while it will start shifting hard at about 3200 RPM's. My thought is that it is vaccum related, but I am not understanding what is going on and what I need to do to correct the problem.

I just wanted to get this back on the list so that I might get some feedback.

Shifty Character?
 

Tref,

Does it shift hard when it's cold, and smooth out after it warms up? And are you talking about all shifts, or just the lower gears? Give us more specific symptoms...

Thanks for the questions.

I shifts hard all the time. Warm or cold and into all gears.

Do you have a vacuum gauge? If so tee it into the black line that goes over the back of the engine to the vacuum modulator.

The vacuum should be high at idle and drop to zero at full throttle. We verify this by driving it. This requires a long line on your vacuum gauge.

The clear/white vacuum line we use can be bought for less than $1.20 a meter from a MB parts department under part# 000 158 14 35. A three way rubber tee is available under the number 117 078 01 45. It lists for $3.60. With 4 meters (maybe only 3 but whats another buck)of line and a tee and vacuum gauge should do these tests.

Hi Steve,

Thanks for the feedback.

I do have a vacuum gauge and the three way connector and some vacuum line. I went through a living hell last summer with a 450SL.

Are you talking about the black line that runs from the connecton on top of the shut off valve to the transmission?

And does it make any difference if I test before or after the shut off valve?

Ed

The vacuum starts at the brake booster supply hose. It takes a detour to the proportional leak at the injection pump. The basic line runs over the back of the motor to the modulator.

If in doubt follow the line up from the vacuum modulator. The control is based upon recreating vacuum readings similar to what a gas motor would give. This is 15-17in at idle to zero at full load.