PeachParts Mercedes-Benz Forum - View Single Post - Persistent clutch issue (long description)

yhliem · #1 08-14-2004, 02:11 AM

I started having a problem with the clutch in my 2.3-16 approx 1-1/2 years ago and several (4) visits to the local dealerships and 2 slave cylinders and a master cylinder later, I'm having the same problem. I'm hoping someone has some idea as to what's causing this.

The symptom is as follows:
At some point, when I go to step on the clutch pedal, the pedal will sink all the way to the floor and stay there without disengaging the clutch.

This condition appears to be temerature dependant because the conditions during which this symptom has occured is usually when the ambient air temperature is quite high (~30-35 deg. C) and the water and oil temperatures are high as well (110 deg C and 110-120 deg C respectively).

The occurence of this symptom is intermittent at first but then, over time, it becomes more and more frequent. Initially, after I manage to pull the clutch pedal back up to its normal position, the clutch will work fine (although the pedal feels a little lighter); however it will progressively worsen until i have to attempt to clutch 5 or 6 times before i am able to disengage the clutch.

The pedal feel during this occurence suggests to me that it is a hydraulic issue. When i step on the clutch, there is initially good pressure feedback. Then, at a certain point in the stroke of the pedal (usually about an inch or so into the stroke) the pressure breaks and the pedal slides to the floor.

When this first happened, I had the slave cylinder replaced. The car was fine for 3 months then the problem came back. This time both the slave AND the master cylinders were replaced. These both occurred last spring/summer.

The car was fine until about 6 weeks ago. it happened again. I nursed my car to the dealership where they checked over the clutch system, bled the hydraulics and reported that no fault was found except a little bit of air in the lines.

Approx 3 weeks later, the problem returned and they once again inspected the system, bled it and reported NFF (No Fault Found) . Tonight, I have had the SAME problem happen twice. Tonight, it almost felt as if when the pressure breaks, the pedal gets sucked to the floor. After having had this happen so often, I can feel whether the pressure will hold or if it will break and tonight, even though I pulled my foot off the pedal immediately the second time it happened, the pedal continued part-way to the floor.

the shop foreman of one of the local MB dealerships has a 2.3-16 as a daily driver as well and he cannot provide any kind of explanation save that my car must be boiling the hydraulic fluid because the can find no evidence of leaks.

I suspect that the fluid in the one or both of the cylinders is bypassing the seals, but is that the problem itself or is there an underlying problem that is causing the bypass?

It seems that temperature is a factor in this because this never occurs in cooler weather, usually only in stop & go rush hour traffic on a hot day. Could the fact that my 16v has been running quite hot for the last year have some connection? For the first 3 years that I owned the car it used to run at a steady water temp of 80 degrees C and oil temp at the same level, but now, water temp doesn't need much to exceed 100 deg C and oil temp is consistently at 110 deg or more. This has developed only in the last year.

Any ideas on where to start are appreciated as this is becoming qite annoying and dangerous.