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The car is a 1991 Mazda Miata with 180,000 Km. These cars have hydraulic clutches.

After engaging and disengaging the clutch repeatedly, the catch point becomes progressively lower until the car starts to creep forward with the clutch pedal fully depressed.

If I pump the clutch repeatedly 5 or 6 times, the catch point returns to a more normal position, and the car no longer creeps forward with the pedal all the way down.

The fluid reservoir is full.

I suspect that the problem is air in the hydraulics lines, but could it be something else?

  • My mechanic was unable to find any leaks in the slave or master cylinders. Noting that the hydraulic fluid was old and discoloured, he replaced it with new. No air was observed while bleeding the system. The symptoms have disappeared, so for the time being I'm going to assume the hydraulics are fine and blame this episode on 20 year old hydraulic fluid. – FishesCycle Jul 18 '14 at 0:32
  • Clutch started failing again soon after. This time I had the master cylinder replaced, and the problem was solved. A bit confusing, as there was no fluid leaking out, but apparently, internal leaks are possible where the fluid finds a way to get "behind" the piston. – FishesCycle Oct 2 '14 at 20:44
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This is symptomatic of worn clutch master or slave cylinder. With the engine off, press the clutch pedal to the floor as slowly and as lightly as you can. If when you release the clutch pedal it is now without any pressure, this proves that the seals are worn out and allowing the clutch fluid to pass by the seals. At this vehicle age it would be advisable to change both cylinders together, assuming no recent work has been done that would involve disconnecting the hydraulics, such as a clutch assembly replacement, to allow air into the system.

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I don't know if you are able to on the Miata clutches, but you could try bleeding the master/slave. If that doesn't work, it sounds like you are going to have to replace the assembly. It sounds like either the master or slave (or both) is getting worn out. The car is over 20 years old. You cannot expect the little mechanical things to last forever.

  • Indeed - it sounds like worn seals on one or the other cylinder... – Nick C Jul 14 '14 at 10:07

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