Clutch Hydraulics confusion

[lamar latrell]

Hello all,

PUMA model Defender 2008.

Bit of a head scratcher here after replacing my clutch master cylinder, I've bled it and had no bubbles coming through for quite a few pumps, but now that I've topped up the reservoir and closed the bleed valve the clutch pedal will still fall to the floor and stay there - i.e. no spring return from the clutch itself.

I'm not losing any fluid or see any leaks.

The original problem displayed similar symptoms where the pedal would fall to the floor - but only after a fair amount of driving without using the clutch, and pumping a couple of times would get it working again.

It is now like this all the time.

(Master cylinder was a relatively easy/cheap 'try it and see' diagnostic.)

I'm wondering how I've made it worse? Or have I just forgotten some simple step in working with the clutch hydraulics?

My only thought is that there is still air in the line and depressing the clutch is compressing that instead of hydraulically activating the slave cylinder - but if I'm not seeing air in the fluid then ??

Any tips appreciated.

[Aragorn]

The force required to push the clutch pedal back over the over-centre spring comes from the clutch pressure plate, and is relayed back thru the hydraulic circuit. Essentially the same pressure you used to operate the clutch is then re-used to push the clutch pedal back. The overcentre spring is a sort of dual action spring, In the resting position its used to hold the clutch pedal up, but once you start pressing the pedal and reach a particular point, the position of the spring then assists you pressing the pedal down, giving a lighter pedal action.

Like you say, if theres air in the line, then insufficient pressure is created in the hydraulic circuit to enable the master cylinder to push the clutch pedal back over the spring as you lift your foot off the pedal, and thus it stays on the floor.

It could ofcourse also be a faulty slave cylinder, a leak or an issue with the clutch pressure plate itself. Essentially anything that stops hydraulic pressure being built up in the system will cause those symptoms.

Try a pressure bleeder or vacuum bleeder instead of pumping the pedal, sometimes air can be stubborn. If that doesnt work then you need to look at the rest of the hydraulic system and then the clutch itself.