car in question is a 79 240d with at least 250k miles. over the past few months have had to pull on the clutch pedal occassionally as it does not return when released. in anticipation of fix have done search and have info on replacement of the master and slave cylinders. the thing failed in the driveway last week. could not get into first gear. over the weekend tried to move the smokey beast into the garage. failure of clutch actuation mechanism was temporaily cured when i steeped on the brake. seems to be working now. is this coincidence? or is there something relating to my steeping on the brake that would indicate one specific component failure? say either the master or the slave? or as pointed out in the archives a 'collapsed hydrolic rubber line? purist philosophy would suggest changing out all parts mentioned. but i am far removed from purist action. thank you.

Most likely the problem is indeed with the hydraulics. Be warned though, I have had a flaky, unpredicatable 240D clutch that turned out to be a broken pressure plate finger that was bouncing around and gumming up the works, that would be an obscure possibility though.

The only way that stepping on the brake may have something to do with it would be by sloshing the fluid level up enough to dump a little fluid down into a leaking clutch hydraulic system.

I would start by topping up the master cylinder and then looking for leaks. Pull down the kick panel and wipe off the master cylinder and lines real well. Then pump the clutch a number of times then check for a leak. There is a soft line and a plastic nipple that connects it through a rubber grommet to the reservoir. The line from the m/c to the slave is metal with a section of braided rubber. I have never seen that line leak, but it is, of course, possible. If you pull the slave cylinder out of the bell housing, you can probably look at it and see if your leak is there.

You can get kits for both cylinders, but don't bother rebuilding them if the cylinders are pitted.

To bleed the system there are several procedures including connecting bleed screw to brake cylinder bleed screw and bleeding backwards. But, I've found that if you just bleed it like you would a brake bleeder, then let it set overnight, the bubbles will come out well enough for it to work well.

Good luck,

My clutch cylinders on my 190E 2.3-16 recently died, and I found out when I went to pick my car up at midnight at the airport. I had to drive home with no clutch, or mostly no clutch, as I had a half can of brake fluid in the trunk from a recent pad change and fluid flush.

If there is a hydraulic reason for the clutch failure it will only be a leak, as there are no other failure modes for the actuators. They can leak for a bunch of reasons, but the reason will be loss of fluid. This is evident as Larry says by checking the brake fluid reservoir. The back half should be empty. If this is not the case then you may have a mechanical reason. While I agree those are less likely, I had a problem when I started using Mobil 1 engine oil in my 1975 240D in the late 70's. The stuff was only available in a 5W grade or something and it leaked past my rear crank seal, causing occasional but nasty clutch chatter. At about 130,000 miles the clutch just hit the floor when I pushed on it and stayed there. I felt something give, and when I checked there was no loss of brake fluid. Turned out the chattering caused one of the circumferentially installed coil springs on the clutch to deform, and as the clutch wore down, that spring got machined down to a dimension that just broke one day. So, there are more mechanical failure types because there are so many mechanical things in the clutch, but they rarely fail because they are kept simple and robust.

Good Luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Another place masters leak in on your feet. Check under the dash and the drivers side floorboards hydraulic fluid.