I have an '83 F250 with a 6.9 Diesel and a granny 4 speed. My problem is after about 100 miles of highway speeds the clutch pedal becomes hard to press and the clutch won't disengage. I've already installed the large reinforcement plate so I don't think that's the problem. Around town or travelling the backroads around here I haven't had any problems. If I let the truck sit for an hour or two it works normally again. Do I just need to install a new clutch? Thanks for any help.

 

I would inspect the line from the clutch master to the slave. Could it have a kink in it that gets worse with heat? You could also crawl under the truck when it fails hot, and open the bleeder on the slave and see if you get fluid when the pedal is depressed. The bleeder is hidden flush on top of the slave, and takes a 5/32 allen wrench to open.

 

Sorry for the long delay. I work nights and the weather has been horrible here. I just checked the tube and don't find any kinks. I've even checked the fluid again just in case. As far as checking things when hot, it seems I can't reproduce the symptoms without going on a long (2hours or more) trip at highway speeds. I did a tour of the local area of about 50 miles and everything worked fine when I got back on surface streets. I'm stumped. Thanks for the wrench size, I've made sure I have one in the truck tool kit and next time I see the GF I'll check it when hot. Really wish I knew what was going on with this. It seems to have gotten worse over time. The first time I noticed it the pedal was a bit hard and there was a bit of grinding when changing gears at a light.

 

Almost sounds like the TO bearing is binding on the input shaft collar/bearing retainer. As the trans heats up, the clearance between the bearing and collar would lessen. If this wasn't coated with grease during the clutch install, the collar or TO bearing inner sleeve could be galling.
I truely suspect that this condition is 1 of the biggest factors in the firewall cracking to begin with. The first cracked firewall I ever saw, back in 83, required a homemade reinforcement plate (ford hadn't discovered the issue, yet) and a new TO bearing & front bearing retainer for the trans. The TO bearing and bearing retainer were so badly galled, they would not seperate, much less move.......
This was at a ford dealer, and is one of the first documented cases of firewall failure with the hydraulic clutch.

 

Perhaps some history is in order here. I've only owned the truck for a year having purchased it last April for $900. By August the firewall problem had cropped up so as to make it undrivable. I had it repaired and have been using it ever since. I do a regular trip to San Jose from the Sacramento area and it's at the end of this trip (both ways) that I experience the problem. I'd be happy to do a clutch job if I knew that would fix the problem once and for all.

On a side note, the pedal effort can change while driving about town. Not in the same way, like it's not working, but just the effort to press the pedal increases and then will suddenly be easy. Almost not requiring effort at all.

 

Hate to say it, but it does sound like the throwout bearing is binding on the input shaft bearing retainer. I believe the factory bearing retainer is aluminum, and there was a cast iron service replacement offered to eliminate this issue.

 

That doesn't sound so bad. I mean other than the obvious R&R of the transmission. I don't mind putting money into the truck, I rather expected to have to. When the weather dries up I'll look into it. Guess it's time to hit the manual and see what's involved. Thanks for the help, I really appreciate it.

 

Yeah, if this is the issue, it's basicaly the same as a clutch/PP/TO bearing replacement, but the front bearing retainer needs replaced at the same time. A decent film of grease on the outside of the bearing retainer will allow the TO bearing sleeve to slide MUCH easier, and should prevent future reccurance.