Peculiar Clutch Behavior

Greetings all:

I have searched the site to find symptoms similar to mine but have been unsuccessful in my attempt so please bear with me. I have a 76B which I have owned now for about two months. If I step on the clutch pedal and hold it down, the clutch will release on its own after about 10 seconds or so. The clutch system is filled with DOT 5, there are no leaks (apparent), and the reservoir level is full. I feel nothing out of the ordinary when depressing or releasing the clutch pedal, aside from the aforementioned autonomous re-engagement.

Have any of you experienced or heard of these symptoms before? Would this typically be due to air, a faulty SC, a faulty MC, or something entirely different?

Thanks in advance.

Regards,

David

from personal (and recent) experience, I would suggest replacing S/C, hose & clutch M/C.... other, wiser folk will likely chime in...

Either the master cylinder or the slave cylinder is allowing fluid past the piston and seal and the pressure from the clutch causes the fluid to move, allowing the clutch to engage. I have the same problem with my Outback. I've just been lazy and haven't fixed it yet. Mine takes a while before the clutch engages just off the floor.

If you're not losing fluid, the master cylinder seal is allowing fluid to go around it. If the bore is fairly clean, the unit can be rebuilt for a few dollars. A new master cylinder is not that expensive however. RAY

Ray X2.

I concur.

Until You get it fixed,neutral at the traffic lights might be a good idea.:D

You don't need another opinion, but it IS the M/C bleeding internally.

It will be your call to either overhaul the cylinder, replace it entirely or deal with the whole system, M/C, slave cylinder and hose, all at once.

BTW: You shouldn't be sitting there with your foot down on the pedal that long. Use the pedal only long enough to engage, disengage or change gears. Longer that that does reduce the life of the release bearing.

Jack

"riding the clutch" also puts undue wear on the thrust bearings.

Thanks, Gents. I appreciate your perspective and help with the diagnosis. Time to get dirty!

dpt

FYI if it is leaking, usually you'll see the hydraulic fluid crystalize either on the slave cylinder or the hose. It'll look almost like it's been bathed in seawater and left to dry. If it is still leaking it'll be wet. :) If the MC was leaking your foot would be getting wet.

Alan, I disagree. With the internal leaks there is no wetness or signs of external leakage.
The leakage is at the (front)internal working seal, not the (rear)external seal. The so-called "crystallization" you describe is not the liquid itself, but rather degradation products produced by DOT 3 or DOT 4 hydraulic fluid reacting with the moisture in air. It won't be seen with DOT5 fluids, though, since DOT 5 is stable with respect to the moisture in air.

Roger that. There is absolutely no external leakage that I could detect.

It could be as simple as the seal on the piston NOT returning far enough within the cylinder when the pedal is released to uncover the bypass hole in the master cylinder. That bypass hole allows the pressure within the clutch system to return to atmospheric pressure, releasing the clutch in its usual timely manner. If the hole gets obstructed, it just slows down the process, giving you the "autonomous" return at its own speed, not the intended one. Similar can happen to brake M/Cs as well, and this is a favorite problem with OE type MGA M/Cs.

Could be the relationship of the seal and the bypass hole has always been marginal, and if the seal has swollen with age, it now covers the bypass hole sufficiently to give you the problem you are experiencing. Good luck.

All, thanks for the help. And the diagram. That helps visualize what's going on inside the MC tremendously.

dpt