I just bought a $1200 '60 F600 Dump Truck today. On the way home from Buckeye to Superior I had to cross the Gonzales Pass. Climbing the grade in 4th @ 60 the truck started to lug and the oil pressure light came on. Not wanting to fry my new toy. I downshifted to 3rd, rather than shift the rear axle to low at road speed. The engine reved the oil light went out, but by the time I got over the top of the grade, she was hot. Of course the guages don't work yet, so I'm going on smell. I stopped at the gas station on Superior and there was a trail of antifreze running back as far as you could see. We added 3 gal water and $35 gas for the 100 mile trip. Leaving the station all was "cool". At the first stop at the top of the hill, all gears are neutral. I caught a tow the last mile home. Parked it on the street, let it cool, started it up and drove it to the back yard. So my conclusion is that the pressure plate gets hot and will not engage until cooled down. Anybody else have any thoughts about this? Have you seen it before? Beautiful truck, but you knew that.

 

It sounds like you've got bigger problems than a bad pressure plate. Where is the water leaking from, and why? Could it be leaking onto the clutch, causing it to slip?

 

Thanks 52Merc. The top seam of the radiator split, so I'm pulling the rad this morning. The radiator is the least of my worries at this point. The amount of water on the ground is not enough to cause the symptom. The clutch does not seem to be slipping it just is not engaging, as if the hydraulics were holding out. After a cool down period the clutch is back to normal. Never any chatter or slipping. I would think a wet plate would tend to slip and grab and then would dry out and act normal once dried. I believe this to be temperature related and either hydraulic or pressure plate related. I'll keep you posted.

 

Usually if it is a problem in the hydraulics, the clutch will not engage. But there is one thing you can check - if the clutch is adjusted so that it has no free play and the pedal (or adjustment of pedal to push rod) is not allowing the clutch master cylinder piston to be in the rearmost position, if the hydraulic fluid heats up due to really hot surroundings it might possibly act as yours did. A check on this would be to crack the bleeder or a fitting to release some fluid when this occurs to see if it allows the clutch to engage.

 

If the truck was parked a long time before you got it, you could have brake (clutch) fluid that is waterlogged, and is boiling at those altitudes when hot. Worth bleeding all the systems just to know what you've got.

 

^These trucks had hydraulic clutches? I thought that wasn't put in vehicles until the '80's?

 

I have an untested theory. There is a small rupture of the inner wall of the clutch master hose causing an embolism which blocks the return flow of fluid when forced back by the slave. This has the effect of holding the clutch down, even thought it is released, thus the symptom. After the pressures have equalized, it takes several clutch applications to reoccure. Temp may be involved, but I no longer feel it is the root cause. I am noow looking for a hydraulic clutch master to slave line or at least the hose that I can splice in. I pulled the radiator this morning. $85 pick it up tomorrow.