Clutch Hydraulic System Woes

[shotwell]

My 1973 220D is having some clutch issues. It started with the clutch pedal not coming back up all the way. On some shifts I had to put my foot behind the pedal and pull it back up or the gears would grind (as the clutch was not disengaging all the way).

After about a week of that and it got worse. One day the pedal went to the floor and never came back up. I had to be towed home.

I did a bunch of reading in threads (on this forum and others) about bleeding the clutch system. I read about the Mercedes way (hose from the brake caliper) and agreed with many others that I wasn't going to do that. I rigged up a system instead with a bicycle pump and a large brake bleeding kit so I could push fluid from the bottom to the top. This seemed to be effective at getting air out of the system...the clutch pedal is working again...sort of. I'm back to having to pull the clutch pedal back about an inch on every shift.

Do I have a failed / failing part or do I just need to bleed my clutch more / differently?

[dirtyharry]

if you're bleeding from the caliper up through the slave into the master, then you're doing it right... I had a similar problem once.. sounds like you've got a failing slave, look for leaks around the slave cylinder. it takes about a 2 or 3ft of vacuum tubing from left front caliper to slave. doesn't take much fluid to bleed it this way. make sure you've got a return spring on the slave and maybe the pedal as well. you can get a new slave O-ring, disassemble slave, use some fine sand paper and brake fluid to clean the bore, then wash with a solvent, then slip seal over the slave piston and lube with brake fluid. assuming the bore of your slave is still decent. or you can just buy a new slave. could be the master, could be flexible rubber line aging, I think its more likely to be the slave.

[t walgamuth]

Well the slave is simple and easy to change and not too expensive but I would suspect the clutch master first. I'd probably go ahead and do the slave first though because the the master is such a triple biatch.

Sounds like you have mastered the hard part though....bleeding the biatch.

[shotwell]

I definitely don't want to just throw parts at it. I want to fix what's wrong...especially with the cost of these parts. I prefer to use genuine MB parts, but will settle with a German parts supplier with a good enough reputation.

I have no leaks in the hydraulic system. I very carefully checked when this problem first started happening.

Someone I know said to go back and bleed the clutch (the same way I was doing it) first with someone holding down the clutch pedal, then again after pulling the pedal back up. Seems like a strange idea to me...anyone ever had to do this?

[Frank Reiner]

Shotwell:

By my reading of your symptoms you are very likely having a mechanical problem rather than a hydraulic one.

With that said, the possible hydraulic problem is a bypassing master cylinder; if you rest your foot on the clutch pedal with less force than is required to disengage, does the pedal sink towards the floor? If yes, there is an internal leak in the master cyl.; fluid is bypassing the cup and returning to the reservoir.

The possible mechanical problems are:
1. A failing pressure plate which does not have enough force to return when pressed fully to the disengaged position. LEAST LIKELY.
2. The over center spring (OCS) at the top of the pedal is adjusted with too much preload FOR THE PRESSURE PLATE'S AVAILABLE FORCE. The over center spring force and the pressure plate force must be in balance. (If the OCS is too loose, you will simply have a stiff pedal.)
3. The eccentric adjustment for the master cyl. push rod has backed off, allowing too much free pedal, hence poor disengagement of the clutch.

[sjefke]

Check really careful for leaks. Brake fluid is very light colored and hard to see. Usually if you don't think you have a leak, you actually have one in the slave because it leaks into the bellhousing of the transmission (and you can't see it).

If I were you I would bite the bullet and replace/overhaul the entire system (slave, master and flex hose) because you will get a nice clean (new) system that would last for a decade plus. If the slave is worn, the master is probably not far behind. And the flex hose can also be getting old and cracked to the point of breaking.

IMHO, I do not see real differences in genuine MB and aftermarket slave or master cylinder. MB does not make these themselves anyway, so I would go with aftermarket if price is an issue. I think a slave and master can probably be had for $50ish each if you shop around. A repair kit runs $20 each probably, so I would save the hassle on the kit and spend the extra few bucks on new cylinders.

And unless you have AAA with free towing, your money on the clutch system will be well spent because any failure in slave, master, flexhose will mean that you will have to pay for a tow. Basic tows here in Atlanta are $70 each.

Good luck,

Bert

[shotwell]

Thanks for the replies guys! The issue has been solved.

Slave cylinder was leaking on the inside to the clutch. When I took it off a whole bunch of fluid came out! I'm sure this hasn't helped my clutch life, but replacing the slave cylinder completely solved the problem. Pedal returns to the top without issue.

Took her out for a drive and picked up some Voodoo Doughnuts! Time to celebrate!

[shotwell]

I drove over 500 miles this weekend. Clutch is working perfectly. I'm so happy!

Thanks again guys.