Dear Tom and Ray:
Our grandson, Matthew, is now driving our old '92 Honda. It's a stick shift. Recently, it wouldn't go into gear, so we took it to our mechanic, and he replaced the clutch master and slave cylinders. That fixed it for a month, but a couple of days ago Matthew couldn't get it into gear again. I had it towed to the mechanic. It was low on fluid, so he bled the line and filled it up, and it works again. But he couldn't find a fluid leak. He said to drive it and at the first hint of the clutch and/or shifter feeling different, I should bring it back in. My question is: What can we do to detect where the fluid leak is? All I can suggest to my grandson is to put some cardboard under the car to look for leaks, or visually check the master and slave cylinders every day. What do you think? — Don
Tom: It was smart of your grandson to get you to throw in the 25-year, 250,000-mile warranty, Don.
Ray: In terms of where the system can leak, there are a limited number of spots.
Tom: One is under the dashboard, where a rod runs from the clutch pedal into the back of the master cylinder. There's a little rubber boot there. If you peel away that boot and wipe your finger where the rod enters the cylinder, it should be dry as a bone.
Ray: If you feel any moisture at all there, the master cylinder is leaking. If your guy used a rebuilt master cylinder instead of a new one, that could happen.
Tom: At the other end of the system, bolted to the transmission housing, you'll see another rod coming out of the slave cylinder that applies pressure to the clutch fork. That also has a rubber boot where the rod goes into the slave cylinder. Same deal there: If you peel away the boot, you should see no evidence of liquid whatsoever.
Ray: Another source of leaking fluid would be the hydraulic lines. Maybe they weren't tightened completely, or maybe one of them got cross-threaded. And, in either case, you'd see evidence of that right at the couplings.
Tom: The final place you could lose fluid is at the bleeder.
Ray: There's a bleeder on the slave cylinder. If that was left open or is faulty, fluid could leak from there.
Tom: But that's it. It's a pretty simple, closed hydraulic system with only a few parts. If you don't find leaks at any of those points, you're not leaking fluid.
Ray: And in that case, I'd suspect that your mechanic made a mistake of some kind when he did the initial repair.
Tom: He could have bled the system incorrectly and left it low on fluid. Or he could have failed to tighten a line properly. And in that case, my guess is that he quietly (or accidentally) corrected the problem when you brought it back a month later, and everything is fine now.
Ray: Time will tell. But if that's what happened, you should have no further warranty claims on the clutch from Matthew.
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)