Clutch hydraulics questions - PeachParts Mercedes-Benz Forum

#1 12-05-2002, 02:39 PM

1. I can't find anything on the MB cd-rom about R&Ring the clutch hydraulics. Is it not there or am I missing it? If it's not there, is it available elsewhere?

2. I've been having clutch problems: once in every 20 times I depress the clutch pedal to the floor, it doesn't return and I have to stick my toe under it and pull it back up. Can't shift while the pedal is down. I pump the pedal a couple of times, and it's fine again.

3. I changed out the master brake cylinder 2 weeks ago, and that's when I first noticed this problem. I thought I'd just gotten air in the clutch hydraulics. But I just flushed & bled the clutch and I'm still having the same problem. (the fluid that came out of the clutch was really gungy. I used a borrowed pressure bleeder)

4. I'm suspicious something might have happened to the clutch master cylinder or the clutch slave cylinder--would it likely just be coincidence with replacing the brake master cylinder?

5. Is the problem more likely to be the clutch master cylinder or the slave cylinder? How can you troubleshoot that?

6. Is replacing either one a complicated job? (I'm maybe an "intermediate novice" at wrenching--not too confident about these jobs.)

All thoughts and suggestions would be appreciated.

Thanks,

#2 12-05-2002, 04:16 PM

Replacing the cylinders is just kind of intuitive, you find the bolts and line connections, disconnect them and remove the part.

There are only two things about the hydraulics you need to know that may not be intuitive. First, at the pedal linkage to the master cylinder, there is an eccentric. You need to adjust the eccentric to ensure that there is no pressure applied to the TO bearing whenever the clutch pedal is released. There is an elaborate hydraulic procedure to do this, but you can simply turn the eccentric until you have a little free play at the pedal and you'll be okay.

Secondly is the bleeding procedure that you have already learned something about. In my experience, if you simply bleed it with the two man method and then let it sit overnight, it will probably be okay. If you let it set after bleeding and watch the m/c reservoir, you will see bubbles working their way into the reservoir. Ensure, of course, that the reservoir is topped off after bleeding so that the bubbles don't come up and decrease the level below the clutch supply line.

Now for the part that you will not want to here. I have experienced exactly what you describe. I went through the hydraulics thoroughly only to have the clutch OCCASIONALLY refuse to release. I finally pulled the transmission and found a broken pressure plate finger rattling around inside and occasionally balling up the works, preventing the clutch from releasing.

I wish I could remember more about what some other symptoms were, but that was almost 20 years ago in my first 240D, a '77 with the Factory clutch that had over 250,000 miles. It was just stress that caused it I believe.

Best of luck,

#3 12-05-2002, 05:12 PM

Thanks, Larry.

The thing that bothers me is that this all started immediately after I replaced the brake master cylinder. My sense is that there has to be a connection, but I can't figure out what it might be. Any troubleshooting thoughts on that?

Thanks,

Ridge · #4 12-05-2002, 06:29 PM

dweller,

I've had problems similar to yours. When the pedal falls all the way to the floor there are two possibilites. One, the master cylinder seals are shot or there is a rusted out spot in the cylinder wall itself. Two, the same conditions exist in the slave cylinder. Whenever I replace one, I always replace the other.

Regarding the excentric in the master cylinder, the Haynes manual has a line drawing of where the excentric should be placed.

The next very important and I mean very important thing about replacing the two cylinders is to use "only" a DOT 4 hydraulic fluid. Any other hydraulic fluid will dissolve the seals in both the cylinders within a year. Take my word for it, as I learned the hard way.

If this doesn't solve your problem, Larry may be right about something sloshing around in the clutch innards.

When you get things worked out, let us know what you found.

By the way, if you get a new slave cylinder make certain that it's the right one by giving the parts clerk the transmission serial number.

Then drain and replace the fluid every year and it'll last longer than you or I.

Ben
www.reproduce100s.com

#5 12-05-2002, 06:58 PM

Thanks for the info, Ben.

Let me ask your opinion a little further. The peculiar thing is that the clutch pedal doesn't ALWAYS fall down. It falls to the floor; then if I pick it up with my toe and pump it, it's back to fine--working normally. I don't quite understand how this could be a bad cylinder. (Not trying to argue--just trying to figure out what's going on.)

Ron Dwelle

#6 12-06-2002, 07:55 AM

If there is LOTS of air in the system, the pedal will indeed stay on the floor. I believe you have air in the system. Since the system had really nasty fluid, I would recommend rebuilding both cylinders, reassemble and bleed. There is no need to replace the whole cylinder unless they are pitted.

Remove both cylinders and disassemble. LIGHTLY hone them, then clean and inspect. If there are pits present in either or both cylinders then replace any pitted cylinders. For a cylinder with no pits, go to a foreign auto parts store and get rebuild kits. These cylinders rebuild easily and rebuild well.

Since DOT4 fluid is much easier to find than it used to be, you might want to use it, but I've never used anything but name brand DOT3 in my 123 cars with no ill effects at all.

Good luck,

Jim Anderson · #7 12-06-2002, 11:21 AM

What did you replace the clutch master with? New, rebuilt, rebuilt yourself?

As to what happens once in a while, my theory...The seals in there when relaxed when just sitting there. When you press the pedal they come under pressure and seat themselves, or in your case, seat themselves most of the time. If they don't seat the fluid just goes by the cylinder and you have to pull it back and try it again. And that theory would apply to both master and slave.

autozen · #8 12-06-2002, 11:45 AM

A trick I learned when I was apprenticing with the Germans. Obtain a top quality oil can like Plews, fill it with brake fluid,attach a short hose, and connect it to the slave cyl bleed screw. Open the screw and pump fluid in until it rises in the reservoir. Close the bleed screw and top off the reservoir. It takes just a few minutes and works every time. If you try to cheap out with an oil can from Kame-Apart or somewhere like that, you'll spend a lot of time and get frustrated. I speak from experience. A cheaply built can won't take the pressure of pushing fluid uphill so the fluid sneaks back past the seal, and nothing goes into the slave cyl. Also when I bleed brakes I let the laws of gravity work for me as long as I'm working on disc brakes.I never understood the fuss about pressure bleeders and such. I just connect a hose to the bleed screw and stick the other end in a special container I have to avoid spills. I guess the arguement for pressure bleeders is speed.I just plan my work so I'm doing something else while the caliper is bleeding.

Peter

PS HI,Ben.

lrg · #9 12-06-2002, 12:28 PM

One other (although unlikely) possibility is you got a bad clutch master cylinder. I once replaced the clutch master on one of my old Triumphs and could not get it to work right. It had some of the same symptoms you describe that I assumed was just air still in the system. I tried for two days and couldn't get it to work properly. After replacing the slave and hoses I tried a new master. It turned out the other "all new" name brand master I had bought had a defective seal. If all else fails double check that the new master you got is good.

Jim Anderson · #10 12-06-2002, 12:34 PM

autozen, thats how I figured out how to bleed (fill) Peugeot hydraulic clutches, kind of. I ran a length of hose from the slave to above the master, stuck a small funnel in the end and pored the fluid in the end. Kind of like bleeding backwards.

#11 12-06-2002, 12:45 PM

Actually, I didn't replace the clutch master cylinder. It was the brake master cylinder--which is where I thought I might have gotten air into the clutch system.

A related question (and for Autozen), when I flushed the clutch hydraulics, I used a pressure bleeder from the top. Is it possible that air could have stayed in the system, with all the new fluid flowing by???

Would it be worth a try to reverse bleed the clutch? I didn't want to reverse bleed it before, since there was so much gungy fluid in the clutch system that I didn't want flowing up into the reservoir (with nice clean ATE fluid in it).

#12 12-06-2002, 01:35 PM

Your best bet for reverse bleeding, given the condition of the fluid in the system, is to suck fluid out of the reservoir so that it is below the level of the clutch nipple. Then remove the hose from the reservoir nipple. Connect a piece of hose to it somehow and run that hose into a drain pan.

THEN do your bottom up flushing and do it THOROUGHLY. This way you don't flush dirty fluid into the brake reservoir. When done, reconnect the hose at the reservoir nipple and fill the reservoir. The little bit of air that will be in the hose from disconnecting the drain line will easily rise into the reservoir in the form of bubbles.

Good luck,

kweimer · #13 12-06-2002, 09:12 PM

Sounds like air still in there to me---especially since this happened just after changing brake master cylinder. Getting all the air out can be frustrating.
Ken

autozen · #14 12-08-2002, 06:16 AM

If you use the oil can approach, you will be sure the system is bled. If you still have problems, it is in one of the two cylinders. Possibly while you were bleeding, some of the gunk that was hanging around in the master cyl got pressure bled down to the slave cyl and is screwing up the seal of the cup in the slave cyl. Actually if you had just disconnected the hose for the clutch from the brake M/C reservoir and layed it aside and then just reconnected it when you were fibished with the brakes, none of this would be happening now. There was no reason to bleed the clutch. I guess this is a moot point now though.

Good luck,
Peter

#15 12-08-2002, 09:28 AM

autozen is absolutely correct. You can lose bunches of fluid from the supply hose and the clutch master cylinder itself with no problem as long as you keep the reservoir full. This is because from the bottom of the clutch m/c up is a straight uphill shot and the bubbles can work their way up. It's between the master and slave where you have bleeding trouble.

Bleeding bottom up is definitely the ideal method, but I've had good success over the years just bleeding it two man method and then letting the bubbles work up into the reservoir.

Good luck,