I have a 2001 Mazda Miata with ~125,000 miles that I purchased in August 2011 and since day one, it’s been making this noise. It sounds like a high pitched chirp or ringing, and it goes away with slight pressure on the clutch pedal. I have tried many things to rectify it but have been unsuccessful. Here’s what I’ve done so far:
- Replaced clutch, throwout bearing, pilot bearing
- Replaced clutch slave cylinder
- Replaced clutch master cylinder
- Replaced clutch fluid
- Bled clutch fluid
Immediately after replacing the clutch, the noise went away, and I went on a long road trip of 2300 miles, but the noise came back about 200 miles from home. I believe I noticed a new behavior at this point also. Previously, before the clutch replacement, the noise was always there. After the clutch replacement, the noise would be there only when the car was cold, and as it warmed up, it would go away. Related to this, the stiffness in the clutch pedal will increase over time: when cold it is very loose and sloppy, and as the car warms up, it will firm up. This doesn’t correspond directly to the car reaching operating temperature (it does so in about 5 mins) but will usually be about 10-15 minutes after starting it.
I suspected that I might have had a bad slave or master cylinder, or air in my lines, which prompted me to replace pretty much everything (except the line itself), but the behavior is no different.
I thought at one point that I simply had the clutch pedal out of adjustment, and this may still be the case. I have adjusted both the pedal rest position and the master cylinder push rod position, and this will solve the problem temporarily, however, after a few weeks to a month, the noise will gradually come back and get worse. For example, just as it starts to come back, the noise is only heard when the engine is between say 2000-3500 RPMs. However, as it gets worse, it’s audible from idle up to about 3500 RPMs (over that the engine is making enough noise to drown it out). That said, as the car warms up, the noise goes away entirely, and the amount of pressure in the pedal is significantly greater (I should note, I do have an aftermarket clutch, but it is supposedly only a Stage 1 and should be close to stock feel).
During our most recent attempt to bleed and adjust the pedal, a friend and I decided to test things out. We found that if you simply press lightly on either the clutch fork or the slave cylinder with your fingers, the noise will go away. The way he described it, it looked as if there was vertical movement in the clutch fork.
This makes some sense to me, as when you put light pressure on the pedal, perhaps 1/8" of travel, the noise goes away. I assume that is simply pressing the slave cylinder push rod against the clutch fork and damping the vibration. Similarly, adjusting the pedal down further would “pre-load” some pressure as well, but my concern with that is that the noise comes back over time, and eventually, I will run out of adjustment for the pedal. I’m also concerned that this may be pre-maturely wearing the new clutch disk.
Our only ideas we have left is either:
- The clutch fluid is poor quality and not entirely incompressible when cold.
- There is flex in the OEM clutch line that allows lower pressure when cold.
- The brand of master/slave cylinder is manufactured with poor tolerances and allow seepage between inner seals (there is no leakage visible externally) but expand when warm to restore full pressure to the system.
- The clutch fork pivot point or springs that hold it in place are worn and allow it to vibrate.
Could we be missing something?