671 Clutch Update

Thanks to all who posted below,,,,,heres more info.

Its a single clutch,,,,,4104 Spicer tranny,,,,,,,,No clutch brake,,,,,,,Push/Pull ??? Heck if I know, there are like 6 adjustable fork fingers that the throw out bearing contacts and it pushes them in toward the flywheel to release the clutch.

The tranny slides in easily like theres not much resistance when the shaft goes into the pilot bearing/bushing,,,,,,,,,right now theres like a 1/4 inch gap from the throw out to those adjustable fork/fingers,,,,,,,,,when the pedal is full depressed it looks like the fork/fingers get compressed say 3/8 inch (from rest position which is that 1/4" from throw out) inward towards the flywheel,,,,,,,,

He told me the old clutch had the same problem of grinding gears which is why he got the new clutch n plate n throw out BUT HE DID NOT CHANGE ANY PILOT BUSHING OR BEARING

Tomorrow AM the tranny will be pulled out (for the 7th time) and my plan is to check the pilot bushing/bearing (replace if in doubt) and how well the plate slides on the shaft,,,,,,and adjust the fork/fingers so theres only like 1/8" from them in rest position to the throw out,,,,,

I can see how if the pilot is a bearing and its sticking/hanging it can make the tranny still spin even if clutch is working otherwise, but if its just a bushing as easy as the tranny goes into the flywheel I dont understand how it could cause the same problem

IF SHE STILL GRINDS GEARS (tranny must still be turning) I MAY PUT A STICK OF DYNAMITE IN IT LOL

Thanks yall I will post back tomorrow after the tranny is out again

John T [email protected]

You said he didn"t change the pilot/bearing and given everything your describing it sounds like thati= is the problem. Most of the trucks I"ve worked on had bearings for the pilot vs a bushing. Given that you said the transmission slid in fairely easily that could easily indicate the bore in the bearing/bushing was worn. With the wear the weight/centrifugal force of the disc acting on the input shaft could be causing it to get cocked in the hole while it"s turning. This, in turn, would tend to keep the shaft turning even when the clutch itself was released. Even if it"s an actual bearing the transmission could still slide in easily like it should but the bearing itself could have a few sticky spots that won"t allow the shaft to turn freely and instead sticks on occasion.

Second idea if the bearing/bushing wasn"t changed there may be trash/gunk/hardened grease built up in the bore of the bearing. Depending on the amount of crud this, again, could be acting on the end of the shaft when the transmission is pulled all the way in and causing it to turn.

If it were me I"d go ahead and pull the transmission back out before spending another minute on it and do what should have been done the first time and change the bearing.

Good luck and keep us posted on the progress.

when the trans is out look very carefully at the splines on the trans input shaft.if they show any

wear,the shaft should be replaced

since the clutch was grinding,when your friend got it,it is very possible the disc hub cant move on the shaft

You've stated that this was the problem that initiated the clutch change in the first place.
Does this bus have a hydraulic master cylinder and slave or...... mechanical linkage?
If hydraulic or mechanical, suspect it first.
Traditionally, as clutch discs wear, the linkage that is used to release them (to shift) gets tight and won't permit the PP to release and hold the disc tight.
This will eventually cause slipping WHEN PULLING.
When you adjust a clutch, you are actually loosening the linkage, wheather mechanical or hydraulic, to give it freeplay.
This is just the OPPOSITE of your problem!
And... so you do just the opposite when adjusting.
I'm with you, the pilot bearing wears looser(more loose?); only wears when you have your foot on the clutch and installed easily, so it probably isn't the problem.
Redouble check the linkage especially if hydraulic.

John I Have it.
There is lost motion in the cluch pedal linkage that is taking up the majority of the travel. The pivot for the pedal, or the bracket it mounts to, ot the rod linkage/bellcrank system, or the fork pivot is worn/loose/broken and flexing. The T/O bearing should move 3/4" or more after touching the fingers. You will find it outside of the work already done. Jim

GM makes differant LENGTH throwout bearings for differant applications.This my have been changed awhile back,hence the grinding because the longer throwout bearing was not used. Hoss

John when you take the clutch out be sure the cluch disc slides freely on the shaft. If not this can cause the disc to hold itself against the flywheel thus causing shaft to keep spinning and grind the gears.

Be sure to check your motor and transmission mounts, if any of them or your cab mounts have settled this will throw your clutch adjustment way off.

Hello John T,
One thing to check and see if it within specs,
measure the outide lip of the flywheel to the disc contact area. Whatever amount is taken off the face, the same amount is taken off the lip, the part where the pressure plate bolts to.
Rebuilt unit? TAKE IT BACK! Get a new one!
Guido.

Hey John,

That 1/4" doesn't sound right to me. Way too much.

But you do puzzle me on your adjustment. On the clutches that I have had to adjust there was a paper included that said what to adjust the levers to when the pressure plate and clutch were bolted down on the flywheel.

You then adjust the linkage accordingly. And I will dare to say even 1/8" sound like plenty. But I must admit I don't know your linkage.

RT (My 2 cents)