I think the master or slave cylinder in my car is going out

[mr.72]

Since the clutch doesn't engage something solid like the brakes do, it's difficult to tell from "feel" whether it has air in it.

Mostly you will tell if it has air in the lines if you drive the car real hard with a whole bunch of shifts and overheat the fluid. At that point the air in the lines would expand quite a bit and you'd end up using the entire travel of the clutch pedal just to compress the air bubbles without actually disengaging the clutch. You would smoke the clutch in an MX-6 long before you get to this point but a Miata or RX-7 on a race track might exhibit this problem. I had this happen in a 240Z once.

BTW it can be kind of a pain carrying in a Miata. Not a lot of extra space in there between your hip and the seat belt anchor. Oh and I discovered my car has a 4" long hole in the top today. Oh joy! Guess I had better patch that up before the weekend, considering we may get some rain. I guess 98K miles, it's about time to have to fix something on this car.

[flintknapper]

Since the clutch doesn't engage something solid like the brakes do, it's difficult to tell from "feel" whether it has air in it.

Actually, when the "clutch" is engaged it is against something very solid (the flywheel), but the clutch isn't involved in the pedal "feel" anyway. What IS felt... is the tension against the springs of the pressure plate.

When you press in the clutch pedal, the springs on the pressure plate are depressed allowing the clutch to free-wheel (spin). When you let the clutch pedal back out, the springs press the pressure plate against the clutch disc which contacts the flywheel.

I think your point was that pressing against the clutch pedal doesn't result in an ever increasing feeling of resistance (gets harder) like with properly working brakes. In fact, at one point...you would probably feel the clutch pedal get lighter (even with a hydraulic system).

So, what he has to rely on...is his tactile memory of how the clutch pedal "normally" feels (amount of pressure and whether the pedal is high or low). A significant amount of air in the system would be readily apparent to most folks unless its been that way for awhile.

Its a simple matter to bleed the system though...(and to NOT inspect it at this point would be irresponsible IMO and just begging for trouble). If either cylinder were to fail while he was trying to come to a stop, then he better have good brakes...because he might not be able to get it out of gear, stall the engine, turn it off, or use the emergency brake in time. Just something to think about. Its so easy to inspect/fix this correctly.

[WarHawk-AVG]

Check the hydraulic clutch reservoir it might be low.

If you change the master cylinder, change the slave, otherwise you will be right back in the vehicle.

I changed both in my '89 Chevy S-10 for right at $75.