"High" clutch pedal problem. Any ideas? - PeachParts Mercedes-Benz Forum

Greg in Oz · #1 06-30-2003, 08:45 PM

A few months back I started a thread regarding replacing the clutch in my 190E, see:
190E clutch replacement. Any tips?
At the end of that thread I concluded that, according to the measuring gauge, the clutch did not require replacement. I still have the problem though, that the clutch pedal is very "high" (ie. the clutch engages at the top of the pedal travel). This seems to vary slightly and my earlier suspicions of some slip were not imagined. Just the other day, under hard acceleration in third gear, when the engine neared its maximum torque at around 3,000 rpm, the revs flared to about 4,000. This was definitely clutch slip as lifting off the power had the revs drop back immediately to around 3,000.

My question is why is this happening. If, according to the measuring gauge, the clutch is not worn out, why is the pedal taking up so high? Why does it also vary slightly so that on some occasions I get slip and not on others? It must be a problem with the clutch release mechanism or the hydraulics. I just don't like pulling things apart without really uderstanding what the problem is. Any ideas would be appreciated.

ejsharp · #2 06-30-2003, 11:14 PM

I suspect that your clutch cable is out of adjustment... but I don't know enough about your system to take a more certain stance. Could also be pressure plate maybe.

Greg in Oz · #3 07-01-2003, 12:18 AM

Quote:

Originally posted by ejsharp
I suspect that your clutch cable is out of adjustment... but I don't know enough about your system to take a more certain stance. Could also be pressure plate maybe.

Thanks for the reply Earl. Mercedes used hydraulic rather than cable actuation for their clutches.

ejsharp · #4 07-01-2003, 01:23 AM

Well I'll try again. What about air in the hydrolic lines? Have you tried to bleed the system? Just a shot in the dark.

MikeTangas · #5 07-01-2003, 02:46 AM

Even on other hydraulic clutches I've worked in the past there was an adjustment. Might possible be located at the pedal, or at the slave.

Let me see what the pictures in the EPC show.

Hard to tell from the EPC pictures. There appears to be no adjustments at the slave, but might be one at the pedal. Sorry I can't be more help there.

Greg in Oz · #6 07-01-2003, 04:01 AM

Mike,
No adjustment I'm aware of. Nor is there any reference to one in the workshop manual.

Earl,
I had considered the possibility of a hydraulic problem although apart from taking up high, the pedal "feels" good. I haven't tried bleeding the hydraulics because:
1. The space around the slave clinder is very tight.
2. From memory, the manual suggests the clutch hydraulics cannot be bled with conventional means and that a pressure bleeder is required (which I don't own).
3. There is no reason for me to believe there is air in the system. Also, if there was I would have thought it would cause difficult clutch dissengagement.

Just the same, I'm appreciative of any ideas and open to all suggestions. Hopefully someone has struck a similar problem before. Thanks for the replies.

#7 07-01-2003, 06:01 AM

The only way the linkage, be it hydraulic or mechanical, can cause slipping is if it is pressing on the pressure plate fingers. This is near impossible with a hydraulic system. I don't know about your car, but on the 123's there is an eccentric at the push rod where it mounts to the pedal lever. This is only there so that you can adjust to ensure that the cylinder rests such that the piston is at the top so that the port is open to the reservoir fluid supply.

I fully expect that the problem is not hydraulic. Air in the system will cause the pedal to be low and prevent the clutch from fully releasing.

Slipping is typically caused by oil on the clutch faces. This is typically the result of a rear main seal or input shaft seal leak. If this is the case, the gauge measurement doesn't matter. The gauge is indicating clutch plate thickness. Regardless how thick the clutch is, it can slip if oilly. Also weak pressure plate springs can cause slippage.

I have never seen slippage caused by a weak pressure plate except in a car that has been driven abusively.

Good luck,

vince · #8 07-01-2003, 10:03 AM

I think Larry is right on. I had a slipping clutch on my 250SL when the clutch components were fine. The transmission input shaft seal was leaking. It doesn't take much leakage, either.

haasman · #9 07-01-2003, 12:34 PM

My experience with clutches with Mercedes is that they tend to wear with the release point moving higher and higher.

If your clutch slips and has a high release point, it sounds like it is worn out.

I have had both good and erroneous measures with clutch wear tools.

Haasman

janko · #10 07-01-2003, 12:57 PM

does anyone have a part number for that "clutch wear indicator"?

ejsharp · #11 07-01-2003, 01:21 PM

My vote goes to Hassman.

ctaylor738 · #12 07-01-2003, 01:28 PM

I believe that the 108 has the eccentric nut adjustment. You need to adjust it so that there are a couple of mm's of play before the clutch mechanism actually starts to move.

You may have a constricted flex line, or your hydraulics may be in poor shape. If the fluid has not been changed regularly it can accumulate moisture which can cause corrosion. This is especially true with the slave cylinder. Either condition could cause the clutch to not engage fully and slip.

Greg in Oz · #13 07-02-2003, 03:38 AM

Thanks for all the replies.

Larry,
Oil contamination is always a possibility, and yes, I do have what appears to be a very minor rear main leak, but I'm talking very minor. It also does not explain the high release point. I will check for any eccentric or other adjustment but cannot recall mention of one in the manual.

Vince,
I hear what you are saying re an oil leak but as I only have the slight one mentioned above (which would be on opposite side of flywheel to clutch). No apparent transmission leak.

Haasman,
Interesting what you say about release point moving higher with wear. That suggests the self adjusting hydraulics don't quite. Also interesting that you mention the clutch can be worn out despite the gauge indicating otherwise. You may be right on the mark with your call.

Janko,
It's a self made gauge (very easy to do). Most manuals give a diagram of the dimensions to cut it out from a piece of sheet metal.

Earl,
I too agree that Haasman may be right.

Chuck,
I will check for any eccentric adjustment as you and Larry suggest. I had considered the hydraulics, but as Larry suggests (and from my previous experience with other cars with hydraulic clutches), hydraulic problems usually cause release problems, the opposite of my problem.

I guess while it is not a major problem, I will be gentle with it and hope that someone may come up with a definite answer. I will be mindful of any slip and not continue driving it if slip does become worse as I don't want to risk damage to the flywheel. I believe the dual mass flywheel as fitted to mine cannot be machined and must be replaced if damaged, something I would rather avoid. When it does become a problem that must be dealt with, unless I have advice otherwise, I will remove the transmission and replace the clutch. While in there I'll also do the rear main seal and front transmission seal. In the meantime keep any ideas coming.

Thanks

Arthur Dalton · #14 07-02-2003, 12:51 PM

A couple of things to consider when working with hyds clutches..

Cutch facings get Glazed from operator riding [ like brake riding]
and hill holding. A glazed clutch will slip like hell, no matter how thick the facing , specially when hot..

Clutch flex hose can constrict [ again, just like a brake line], and act as a one way valve.. you can push the clutch in with the high pressure of the master, but the RETURN pressue is from the spring of the pressure plate,, not much, in comparison, specially as the plate gets to its full engaged end..so, a restricted hose can cause a slipping clutch..[ there is a pedal return spring , but nil effect on this factor]
A test here is to have someone push/release the pedal and then you immediatly open the slave bleeder ...if the slave is still under pressure w/pedal up, you have a restricted hose..that will usually slowly bleed off.

Usually, a worn clutch will both slip and catch higher and higher as it wears.
And sometimes , it is just a combo of slight glaze disc, worn plate surface [ heat checked] and fatiqued pressure plate springs.
A good rule is alway replace all three [ plate,disc,bearing]