'97 F150 - clutch won't engage when hot
 

It was hot here yesterday (around 100), and I was going home from a buddies place. I stopped at the store (after a 30-40 min. drive) to pick something up. When I came back out I couldn't get my truck into gear (manual tranny). Shifter worked fine, but acted like it was in neutral. I topped up the master cylinder with brake fluid and was able to crawl home at 15mph.

I go out this morning while the temps are cooler to start checking it out and it's acting normal again. Goes right into gear and moves. No fluid loss either.

At first I was thinking a bad slave cylinder, but now I'm thinking master. What do y'all think?

Do you see any leaks? If the slave is leaking, there will be fluid dripping out of the bottom of the bellhousing. If the master is leaking, it will be leaking inside the cab above/behind the pedal.

Did the pedal have a normal FEEL? If so, and it went into gear with the engine off, the pilot bearing may be sticking.

No leaks that I can see. I ran 2 or 3 reservoirs of fluid thru it to flush it out. Haven't had a chance to drive it yet. I'll keep y'all posted.

Back from the dead. Had the same issue yesterday, except this time the clutch master cylinder hadn't lost any fluid. Had to have it towed home yesterday, but went out this morning and clutch is working again.

Was out running around yesterday, and clutch pedal started to feel different (harder to push in, I think), before it finally went out and I couldn't get it into gear. I don't see any leaks or drips around the master or bell housing.

Any ideas?

The clutch doesn't consume much fluid at all. If there wasn't any fluid in the reservoir before there must be a leak somewhere. Fill it up, bleed it and mark the level. Check the level in a few days. It might be leaking slowly enough that it's hard to find a drip from the bell housing.

Thanks for the reply. Seeing as how the truck is over 18 years old now, I'm just going to put a new slave in it, and replace the clutch and rear main seal while I'm at it.