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I've got a customer who came in complaining that the clutch pedal had gone 'funny': it wasn't 'coming back up' like it used to. As he was in for service anyway, we replaced the clutch fluid, and it 'seemed ok' afterwards.

He came back a few weeks later saying that he was having problems with the clutch being 'random'. In the morning, the clutch doesn't disengage properly when he fully depresses the pedal (he has to be in neutral to start the car), but after a few miles of driving, it works ok.

He wondered whether it wasn't the difference between the car being 'warmed up or not', so we kept the car overnight to try, but haven't been able to see any problem.

What are we missing?

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3 Answers

Sounds like the clutch master cylinder is leaking. If you pump up the pedal with your foot, it might retain pressure for you to drive for a while, but after it sits, the symptoms will return.

Time to replace the clutch master cylinder or check for brake line leaks.

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Apart from NoCarrier's good point about the master cylinder, the other side might also be a problem: the slave cylinder. I had an older Triumph that needed both ends fixed to finally fix the clutch.

It turned out the slave cylinder walls had developed rust, which gradually wore down the seals. Having the slave re-sleeved (and new seals!) was also necessary.

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On my cars I try to replace both as a set if the slave is external. Always seems like once you repair one side, the other fails right afterwards. I've never had much luck with rebuild kits either. –  kkeilman Mar 12 '11 at 2:34
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OK, gotta come clean on this one.

The "customer" was me.

In the end, I drove for so long with a 'dicky' clutch that it wore out, and they ended up replacing the clutch (and you all know how much that costs).

Not long after, the problem started again.

Thinking it over with a friend, we worked out that the pedal "going funny" was the clutch pedal return spring which was broken (TBH I didn't know such a thing existed). This meant that the only thing bringing the pedal back up was the pressure from the cylinder, so it lost pressure over time. I guess that the momentum of the pedal during gear changes meant that after a couple of miles things seemed normal again, and when they tried it in the garage, maybe they just knocked the pedal when they got in the car.

Anyway, for several months, I just pulled the pedal up with my foot every time I started the car, and never had any more problems. After that, I went and bought the clutch return spring myself and replaced it. It took me about an hour to work out how to do it, but it cost me 190 times less than the clutch replacement did.

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For others reading this post, I feel obligated to say that most cars with a hydraulic clutch do not have a 'secondary' clutch return spring, but rather use the spring force of the pressure plate (inside the transmission) to provide the 'pedal feel'. I imagine that searching for a clutch spring in the car would be a bit frustrating if it didn't actually exist. –  JeremyP Mar 16 '11 at 4:36
    
@JeremyP. Thanks for adding that. (Something else I didn't know!) –  Benjol Mar 16 '11 at 6:13
    
Most cars do have a "clutch pedal spring", but it's only there for anti-rattle purposes. The clutch system pressure is supposed to keep the pedal up in your typical car. –  Brian Knoblauch Jun 2 '11 at 18:42
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