My 79 F600 has a problem when I push the clutch pedal all the way to the floor the clutch won't release and it's hard to change gears. This happened a few months ago and I adjusted the clutch and fixed it, but it's happened again and I've adjusted the clutch all the way to the back of the adjusting rod and it's not better. Any ideas of what the problem is? Thanks!!

 

Lost motion in the linkage? There are several wear points. You might know this already, but for those who follow who might not . . .

First things first: how much free play do you have at the top of the pedal? Standing outside the cab, reach in with your right hand and press the pedal. How far does the pedal travel before significant resistance is felt? There should be 1/2-1" of free play, where the only thing moving the pedal does is take up the slack in all the components of the linkage, and begin to move the throwout bearing forward to touch the clutch fingers. If you don't have any free play, the TO bearing wears out prematurely (and if out of adjustment far enough, the clutch can slip, eventually burning it up). If you have too much free play, the clutch pedal's working range is reduced and the clutch may not fully disengage.

For reference:




1) The vertical rod (7521, Clutch Pedal to Bellcrank). The bushings on either end (7526, in yellow above) are plastic and when they wear out, the rod ends wear and eventually break off, and the holes where the rod ends fit elongate. You can lose a lot of motion taking up all that wear when you press the pedal. I replaced mine with brass bushings (in this post).

2) The Bellcrank (7228) has brackets (7507 and 7A572, depending on your Bellcrank style; two are shown above) on the frame and engine ends (in lavender above) and if their bolts have come loose they'll move around and lose you some motion.

3) The bellcrank split bushings (7517, 7/8" ID x 1" OD x 19/32" lg.) might be missing or partially missing. That lets the bellcrank move fore/aft instead of moving the horizontal rod.

I would think those to be the most common linkage issues. The bushings at the top of the clutch pedal (2461, where the clutch & brake pedal hinges) aren't usually worn enough to affect operation, though rust can form and make the pedal stiff, preventing the pedal from returning up fully, which is an issue that should be fixed if present; mine was pretty bad when I bought it, and I removed the cross shaft 7506 and polished it up, reinstalled it greased.

I've seen a couple of cases of a cracked bellcrank (not on an F600) where when you press the pedal, the crack opens up and loses some motion, but that's an edge case.

The clutch disc and pressure plate parts might be damaged themselves. A broken or bent clutch finger, for example. These clutches are pretty tough, though.

 

Thanks! I haven't measured the free play but the pedal feels normal, just the clutch itself doesn't release even when the pedal is all the way to the floor. Is it possible the throwout bearing could be bad? I don't have a transmission jack but if I got one, how difficult of a job would it be to get into the clutch assembly? Also how difficult are clutch parts to find on this truck?

 

Clutch parts (TO bearing, pressure plate, disc) are readily available. Flywheels, not so much.

A failed TO bearing cannot cause the symptom you describe, unless it has completely grenaded, and you will have lots and lots of noise if you depress the pedal with a grenaded TO bearing. They generally just scream or squeak when asked to turn under load (eg when you press the pedal) and give you lots of warning of their demise. Left alone, they can spin and wear out the fork, but again . . . noise.

Maybe someone with more experience with this particular clutch will pipe up as to access without removing things.

In the dim, dark past I ran into some foreign car that had a cracked fork that ate up some of the pedal travel silently, but that was a real oddball.

 

I think we found the problem. Look to the left of the 2 bolts and a piece is cracked. How hard is it to get off and is there a replacement part available? I weld so worst case scenario I can weld it back

 

Yours being a '79 with the Lima engine (if it's a gas engine), I'm unfamiliar with it. Note that there is a missing exhaust manifold bolt, too.

For a gas engine, that bracket is new for 1979 and does not interchange with older years (as previous to '79 the gas engines are FT or Six engines): D9HZ-7A572-E. There are two listed on eBay right now, ranging from $60-77 (plus tax, if applicable in your state).
https://www.ebay.com/sch/i.html?_nkw=D9HZ-7A572-E

IDK about R&R labor. From here, it looks like it's not awful, unlike R&R that F600 steering box, where you have to basically unbolt the engine/trans and shift it to the passenger side to gain enough clearance to get the box out, and that means taking out the cab floor around the shifter (on an MT truck).

OTOH, once you have it out, as you weld it would be a snap to prep and weld it back together, then reinforce it.