Not a clutch performance

I recently returned from a trip to find that my car had been vandalized, or perhaps ineptedly plundered for parts. The worst problem was that the clutch pedal was nearly to the floor, and shifting was almost impossible. So, I brought the car to a local mechanic, who replaced the clutch master cylinder. That fixed the problem for about 30 miles. When the same problem returned, I brought it back, and they again replaced the m.c. Unfortunately, 30 miles later, I could again no longer shift. Any thoughts on what these guys are missing?

The slave cylinder.

I am not sure if the mechanics looked at that - I guess I can ask. Do you think a faulty slave cylinder would explain why the clutch works for a week or so, and then fails again?

Yup. It’s basically the same as the master cylinder only on the other end of the system.

Both have a piston filled with hydraulic fluid with a tube between them. Passage of the fluid past the internal piston seal of either will have the same effect. And yes, it can happend without loss of fluid to the outside world. And it can happen intermittantly.

Thanks. The problem isn’t really intermittant; once the hydraulic system fails, it does not return to working at some later point. What has happened is that it works for about 30 or 40 miles after the mechanics replace the master cylinder, then it fails, and I take it back to them. I am now on the 4th master cylinder, at least according to the repair shop.

Your master cylinder is not fully retracting when you take your foot off the pedal.
It needs to retract to refill the system from the reservoir.
Maybe there is a return spring broken or missing, or some part of the pedal linkage bent or binding.
Does the pedal spring back up to the same height as the brake pedal?

Right now (5 miles into the 3rd new master cylinder), the clutch works fine, and the pedal behaves normally. However, based on the 2 previous m.cs., this may change. For both of the two previous new m.cs., after the first few days, the clutch pedal still returned to normal height, but it had a lot of free play between normal height and the point at which it engaged. Over time, the engagement point got closer to the floor, until it eventually almost rested on the floor, and I could not shift at all.

Thanks for your input.

BTW, I am now several hundred miles into the 3rd new mc, and it is still working. After this final repair, the mechanic said something about some damper that he had failed to adjust during the previous repairs. I don’t really know what he was referring to, or whether that mattered, but so far, so good.