126,500 on a Mercedes 300D Turbo Diesel. The transmission is jerky upshifting between all gears and there is a slight growl between third and fourth. I just had the fluid and filter changed by a dealership which did not solve the problem. Would this be internal or external, vacuum or mechanical. I'm 15 and just learning and my Dad doesn't fully comprehend the intricacies of Mercedes Benz engineering. (though he did spring for half of the car)

 

The growl may or may not be in the trans. Even with a poor service record those trans. should last to around 180K. More if the fluid and filter are changed at the 30k intervals. If the upshift is hard for all gears then your modulator is either not getting vaccum or is adjusted too tight. Find the vacuum hose that goes down to the tranny on the driver's side. Trace it up to where it connects on the engine. Disconnect the hose there and plug in a vacuum guage. Run the engine and check what the guage reads. It should have somewhere around 10 inches of vacuum. Quickly pull the throttle linkage wide open and release before the engine races. When you do the gauge reading shold drop to almost 0 inches of vacuum. If that checks out then the vacuum supply is good. The problem is either modulator adjustment or vacuum leaking from the modulator. Take the line going down to the trans and see if it holds vacuum. If it does you need to adjust the modulator. If not then get underneath find the round part the line goes to. That is the modulator. The mod. has a rubber cap that tends to crack and leak vacuum. Replace it if it even looks like it could leak vacuum. Retest the modulator to see if it holds vacuum now. If it doesn't the internal diaphram is shot and the modulator needs replaced. If it holds vacuum now but still shifts hard then you need to adjust the modulator. Under the rubber cap you you'll notice a "T" shaped key that rests in grooves. Pull that key out just enough to clear the grooves. Note it's position and turn it out 1/2 turn and test drive. It should shift softer now. Continue to adjust (in harder, out softer) until you are comfortable with the shift. MOST IMPORTANTLY, DO NOT attempt to adjust the modulator if you do not meet all of the vacuum critera first.

 

HOW THE REV????SLOW RATTLY???REV CLUCHES DONT LAST 120K ..I REBUILD THEM FOR A LIVEN....GOT TWO IM DOING RIGHT NOW.21 YR. EXP