New issue with 5-speed manual in W201 - difficult shifting - PeachParts Mercedes-Benz Forum

Greg in Oz · #5 06-12-2006, 10:48 PM

Thanks Larry and Brian for your replies. They both sound plausible given the symptoms however I am now in a position to give you some more information as on the weekend I explored the problem further.

Selector linkage bushes all look and feel fine. Gearbox fluid level is full. I did notice that the gearbox input shaft seal must be leaking slightly though as there is evidence of transmission fluid (red) drips from the bell housing area. Previously drips from this area were clutch hydraulic fluid however the replacement slave cylinder has rectified that.

A test drive in a quiet area allowed me to investigate the problem further. I earlier stated that I believed it was not a clutch dragging (ie. disengagement/release) issue. Well I now believe it is. Strangely, it only occurs when the engine is at higher speeds. As I mentioned, gear selection is not a problem with the engine at idle. As the engine speed increases so does the difficultly in shifting gears. I have also determined that the problem occurs in any gear, not just 1st and 2nd. It is more noticeable in 1st and 2nd because these are the gears where higher engine speeds are used when accelerating from a standstill. If the car is driven to higher speeds then the same difficulty is experienced with selection of 3rd, 4th and 5th.

The problem, put simply, is that the clutch with not release with the engine spinning at higher speeds. If the engine is taken as high as say 4000 to 5000 RPM it is not possible to release the clutch to shift gears. If the car is allowed to slow such the that the engine speed decreases sufficiently then eventually the clutch will release. In fact, engine braking can still be achieved at higher engine speeds even though the clutch pedal is depressed!

Likewise, if the engine is revved above say 2000 to 3000 RPM in neutral, it is not possible to disengage the clutch to allow any gear to be selected until such time as the engine speed is allowed to drop back to idle speed. I appreciate this is not something someone would normally do, I simply use it as a means of demonstrating the problem. The clutch is behaving almost like a centrifugal clutch or the torque convertor on an automatic except for the fact that once released the clutch will remain that way.

I will next try bleeding the clutch hydraulics again to confirm that is not the cause, however I would have thought that a hydraulic issue would exist irrespective of engine speed. As I mentioned, with the engine idling gear selection is fine without any suggestion of baulkiness. Any clutch drag at idle would certainly show up with a crunch when selecting reverse however this is not the case. Rev the engine much above idle and selection of reverse is met with a crunch and selection of any other gear gets more difficult as the engine speed increases. The clutch pedal "feel" is perfectly normal.

Just something else that may be worth mentioning is that previously the clutch had a shudder problem that could only be avoided by getting the revs just right when moving off from a standstill. This problem was always worse when cold, when the car had sat unused for a few days, and in very humid or wet weather. The problem improved somewhat following replacement of the slave cylinder which I attributed possibly to the bell housing no longer being contaminated with hydraulic fluid. Since this latest problem suddenly appeared, the clutch shudder problem has completely disappeared.

The sudden apperance of one one problem and disappearance of another, and the engine speed sensitive nature of the problem makes me wonder if it is a mechanical issue with the clutch (rather than say a hydraulic one). For what it's worth I should also mention that being a 1990 model the car runs the "newer" version of the W124/201 gearbox and clutch with the dual mass flywheel.

Keep the helpful suggestions coming!

Thanks,
Greg