W123 Clutch hydraulics (?) misbehaving

[tsa]

More great advice on part numbers and where to source from, many thanks.

Also great tip on re-using the old piston rod if the one in the new one isn't of the same length. I've previously rebuilt ATE brake calipers & master cylinders on my bikes, so have a little experience with that. On the latter, the piston assembly is held in place with a circlip, but on some of the pictured no-name aftermarket cylinders it looked like a star-like washer thing keeps it together; it didn't look like it was designed to be taken out and re-used.

My MB dealer could get an original slave cylinder in a week, and for £50.16, so I decided on that option. To me, it looks like the aftermarket pattern business has changed quite a bit the last 5-10 years, with loads of poorly documented cheap (sometimes) parts around. And sometimes identically looking parts not really any cheaper, either.

In one of the pictures grober posted, I could see that the two bolts that hold the cylinder to the bell housing take a 13 mm ring spanner. I assume the one for the hyraulic line needs the special open-ended 11-mm one? Probably best to undo the line first. My normal approach would be to run the engine to operating temperature, with the aim to warm up the bell housing a little (relative thermal expansion etc. to help bolts that haven't moved in 32.5 years) before undoing the 13 mm headed bolts, but this is perhaps not necessary?

 

[grober]

A decent 13mm ringer should be fine if you can get it on to the bolt head right. That said its a steel bolt into an alloy casting so there might be a bit of galvanic corrosion- its a try it and see situation I guess

 

[tsa]

Well, it took a while, but I hope that I've finally managed to get my clutch hydraulics fixed.

Some mental notes I made underways;

a) whilst the flare nuts on the brake master cylinder are 11 mm ones, the one on top of the clutch slave cylinder turned out to be a 12 mm one. Why standardise something if you can avoid it? I chose to swap the 11 mm Halfords pro spanner i bought for this job for a 12 mm one to avoid rounding off the nut. Delay only one day

b) I should have heeded Druk's advice that the plastic shim under the slave cylinder flange may come out in pieces. Mine didn't, but had become sufficiently brittle so it broke when I accidentally bent it a little when cleaning it. It would have helped if the MB parts guy had recommended I get a new one from them together with the new slave cylinder. This plastic shim has a slot in it which serves as access for a tool to monitor wear of the clutch friction disc. I opted to skip that possibility by making up something myself, of what hopefully is temperature stable plastic. Old one was 2.3 mm thick, the new is hopefully close enough at 2.6.

c) main hassle with the job was jacking up the car securely when on the driveway outside my house, without access to a garage lift.

d) the old slave cylinder seal had probably been leaking for a while before it popped; the drain hole at the bottom of the bell housing was wet with brake fluid. This may have found it's way to the clutch friction disc; will this wear off by itself?

e) I saw absolutely no signs of leaks at the master cylinder, so I'll keep my fingers crossed that this has avoided deteriorating . . .

Once again, thanks a lot for the advice you guys have provided!

 

[grober]

d) the old slave cylinder seal had probably been leaking for a while before it popped; the drain hole at the bottom of the bell housing was wet with brake fluid. This may have found it's way to the clutch friction disc; will this wear off by itself?

Its a question of how much fluid gets on to the driven/friction plate. A little at a time is likely to be burnt off- saturated would be bad news. Again if it seems to operate OK then just go with it---- till it doesn't and you start to get symptoms- its unlikely to fail completely without warning.

 

[tsa]

Its a question of how much fluid gets on to the driven/friction plate. A little at a time is likely to be burnt off- saturated would be bad news. Again if it seems to operate OK then just go with it---- . . . . .

Now after nearly a year and around 1500 miles later, the judder I felt when engaging the clutch has gradually got less noticeable, so I hope I got the new slave cylinder fitted in time to avoid having to replace the friction disc.

Otherwise, just before setting off when moving house, the disengagement point of the clutch pedal began feeling less distinct. First, I sometimes had to press the pedal twice to disengage, then this became SOP, and now one to three pumping's on the pedal is the rule to disengage. I remember the advice to also replace the master cylinder whilst "doing the clutch hydraulics", since it is likely to fail soon after the other one. But I'd thought the signs of the master cylinder failing was more abrupt - i.e. going from working to not working at all? Like what happened when my slave cylinder failed. Yesterday I had a look at the master cylinder and the surrounding area; no major leaks / excessive fluid noticeable (the braided rubber hose from the reservoir was more "wet" than the cylinder body and the area around or below it. No visible drop in fluid level at the reservoir.

I'll round off with the short version of my question; is the described erratic behaviour of the clutch pedal the usual signs of the master cylinder failing?