Clutch pedal occasionally goes solid

Weird problem with clutch. New master and slave cylinders. But pedal goes solid sometimes and clutch engages high on the pedal on occasion. Any ideas folks?

I suspect you may have the clutch slave cylinder that has the piston with integral seal on it plus a very strong internal spring. This is what I have.

The spring, when compressed gets coil bound and the piston cannot retract any further. But then the coil bound spring can bulge to one side, which then allows the piston to retract further.

When the pedal goes hard, it could be the piston has retracted and the internal spring is coil bound but not bulging.

When the pedal is not hard, it could be the spring is coil bound and bulging which allows the piston to retract further thus giving you free play in the pedal.

A way to check this is to take out the spring from the slave. Pretty easy and you need not take the slave cylinder out to do it

69 OTS


Tweety occasionally did that, and even after I had the slave and master rebuilt, they occasionally did it. I could never figure out what the deal was!

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It’s just a guess, but it could be the rubber clutch hose. We’ve seen this with brakes from time to time… the hose swells internally and locks some fluid in the brake caliper. In a similar way, the rubber hose in the clutch system could be swelling, locking some fluid in the slave. When the pedal is released, the fluid is replenished from the reservoir. Then the next time you push, you have a high pedal and quick engagement. That hose is a bear to change, but it may be worth the effort.

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Definitely the flex hose has de-laminated internally.

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Nope, not always: I changed the hose twice, once before the cylinder rebuild (back in the late 70s), and once after the rebuild (~2010). It would still do the same thing.

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I had that problem. It was a blockage. In my case, worse than just a plugged line. The seat of master’s output port had corroded enough that it collapsed and obstructed the port hole badly.

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Thanks guys! I was thinking along similar lines. I’ll replace the flexi first, then if that doesn’t work look at the slave cylinder. I ordered (another) new master cyl, as the one on there is a cheapo one. No harm in having spares on the shelf ! Glad This prob has come up before and it’s hydraulics related.I don’t want to take the engine out again just yet !!!

Replaced flexi hose, new hose from reservoir. Cleaned out slave cyl And reservoir. Lots of muck. New fluid. Clutch is lovely! Jag lovers is GREAT!!