Clutch pedal goes soft ('88 Reynard)

[John P]

Hello -

I'm troubleshooting an issue that recently appeared on our CM car (1988 Reynard FF). I’ve discovered that if you hold the clutch pedal down after 14 seconds (yes, I timed it and it's repeatable), the pedal goes soft and the clutch slowly reengages (very smoothly I might add). A quick release of the pedal and repress and the pedal is firm and the clutch releases properly. I tried holding the pedal halfway and you can feel it just slowly go soft like you are losing pressure in the line. If you are quick on the pedal it is nice and firm and you'd never know there was a problem; I only discoved the issue while loading the car on the trailer where I had the clutch pressed for >10 seconds. Now I'm afraid we are a clutch press away from no more pedal.....

Now the strange part - I can't find any fluid leaking and the clutch Master cylinder stays full. I've pumped many times to see if I could find a leak around the MC or the line anywhere and if there is a leak it's microscopic. I can't find a drop of fluid back from the master all the way back to the line into the internal slave (though can't look without separating/pulling the engine). However, since the MC stays full I'm not sure even if I could see the slave I would find a leak anyway..... I suspect it must be an internal failure of the master or slave given I'm not losing fluid... but which is it, the master or the slave (or both)?

Just to be sure I went ahead and bled the system to see if it would make any improvement and it didn’t. Exact same 14 seconds until the pedal starts to lose pressure. So short of just changing out the master and hoping there is an internal leak there and if it doesn't fix the problem then go ahead with the task of changing the slave (which I really don't want to have to pull the engine/transaxle to do)..... is there anything else I should check first here, or anyway to isolate where the failure is?

Thanks,
John P.

[-pru-]

John,

Sounds like a failing Master Cylinder. That is, the Master can build but not hold pressure.

I had the same issue in my early days with the DB1. When I did the ground up on the car, I replaced the old Lockheed "tin can" Masters for both the front and rear with new Girling but simply rebuilt (new seals) the Lockheed clutch. Clutch worked fine for a few years and then suddenly failed (at the Solo Nationals of all places) as you described. Replaced with new Girling and never had another issue.

Take care,

[J Leonard]

Plug line to slave, see if master holds pressure?

[kea]

No leak, change the master cylinder.
Also, remember to swap the push-rods, as that cylinder uses a length shorter then normal.

[Lynn]

A new Girling master cylinder solved the problem. Thanks for the advice.

[evildky]

I had the same issue on a street car. the master was bleeding off. I took it apart and upon closer inspection there were a tiny nib sticking into the bore where the hole feeds from the reservoir. It had shaved a tiny bit off the edge of the piston seal. so it would make pressure but that one weak spot in the seal allowed it to bleed off very slowly.