intermittent clutch failure

[gerryball3700]

can anyone help. i have lacetti 16sx 04 31000 miles hardley ever used. after a long journey on the motorway (not using clutch) when i come to use the clutch the pedal goes to the floor. i can recover the clutch by pumping. town use does not affect it. my mechanic has changed the fluid and for the last 1000 miles there has been no fluid loss or any signs of blead from the upper cylinder or gear box.

[Fltofancy]

Sounds like you have a master cylinder or slave cylinder internal seal failure. Could be either the master cylinder or Slave cylinder, hard to tell which. Replace or rebuild both is about the only way to fix.

Fltofancy.

[gerryball3700]

thanks Fltofancy but just to satisfy my enquiring mind why do you think i am not noticing any fluid loss and also when i am using the clutch on a regular basis why do you think the problem is not arising.

[Fltofancy]

No fluid loss is because the leak is internal. That is fluid is bypassing one or both pistons inside its respective cylinder housing, either the clutch master cylinder or the slave cylinder because the seal (o-ring likely) is bad or you have some pitting on the cylinder wall. No fluid is escaping outside of the cylinders but you cant build pressure in the master cylinder, or hold pressure in the slave cylinder. Had the very same thing happen on a motorcycle one time due to corrosion in the master cylinder.

The reason it is intermittent and better when used often is because when the system isnt used some flued "leaks" around the seals (all internally) and when you press the clutch pedal the fluid is partially forced onto the correct side of the piston during the return stroke. You may notice the clutch acts better after you pump it several times. This gets the fluid on the correct side of the piston(s). Also remember moving fluid makes its own seal to some degree, although much weaker than a good o-ring.

All of this speculation is assuming you dont have air in the system. If your clutch reservoir has ever been low you may have air trapped in the system which will cause similiar problems.

Fltofancy

[gerryball3700]

Thankyou Fltofancy if i think about it long enough this has to be the problem. Thanks for giving me the benefit of you obvious extensive knowledge. would i be pushing my luck if i asked you if there was any easy way of determining which cylinder it might be causing the problem as i believe one of them is in the gear box !!!!!!!! expensive.

[Fltofancy]

No easy way to tell which one for sure. Although the master cylinder is usually the culprit more often than the slave cylinder. Sometimes you can listen to the cylinders with a mechanics stethascope while someone is pushing the clutch and hear a hissing sound as the fluid escapes around the seals.
Change the one thats easy to get to first and see what happens, you got a 50/50 chance of getting the right one.

Fltofancy

[gerryball3700]

Thanks very much for your help will let you know the outcome

[Fltofancy]

Wish we knew how this turned out.

Fltofancy