OT 671 Detroit Clutch Problem

My 81 year old buddy has a 60’s model 671 Detroit Diesel (Bus RV conversion) with a 4104 4 speed tranny and he can NOT get the new clutch to release properly so the gears can be shifted even when setting still and clutched to put it in gear, the tranny is still turning and the gears have to grind grind grind……..

He installed a new clutch disk,,,,,,,,pressure plate,,,,,,,,,throw out bearing,,,,,,,,,had the flywheel machined smooth. We have adjusted the 6 adjustable fingers (that mate to throw out bearing when clutch is depressed) every which way but loose and adjusted the clutch pedal linkage every way possible in and out tight and loose all to no avail. Currently the fingers are adjusted like ¼ inch away from throw out bearing (i.e. it ONLY turns when clutch is depressed) and when he depresses the clutch pedal to floor the throw out comes forward and pushes the fingers about ¼ inch or more and the springs compress and in theory the clutch disk should be free and NOT turn the tranny so he can shift but Nooooooooooooooooo the gears still grind grind grind SOOOOOOOOOOO we keep adjusting/tightening the clutch rod to pedal linkage to get more forward throw out travel to push fingers deeper and she grinds less butttttttttttttttt then when the pedal is released the fingers are too close to the throw out and it spins constantly (only should when clutch is depressed)……… If we adjusted the fingers farther away from throw out (to stop its turning when pedal released) that wouldn’t help cuz then we just have to adjust/make the linkage move further to push the fingers deeper so the springs compress to release the clutch, i.e. it don’t accomplish anything it seems grrrrrrrrrrrrrrr

Like I said we have adjusted the 6 fingers per the book and NOT per the book and adjusted the pedal rod slack tight n loose everywhere AND SHE WILL NOT RELEASE so the gears can be shifted REGARDLESS WHERE WE SET EITHER ADJUSTMENT

Its drivin me to drink as I don’t have enough hair to pull out. Anyone experienced with Detroit 671 clutches that can shed light on why it don’t release so the gears stop turning and grinddddddddddddddd

Ol John T NOT a clutch kinda guy

Did he replace the pilot bearing?

Did he install the clutch disc backwards?

That is not a DD clutch. They didn't make clutches. The vehicle mfg could have chosen from several clutch mfgs.

I have had similar problems just putting a clutch in my old chevy pickup.

I put it in gear and kept the clutch depressed (disengaged) and started it. Just be sure you are somewhere where you have time to react if it does move. Don't know why... clean everything, put it togther and it sticks.

He DID NOT replace the pilot bearing,,,,,The disk is NOT backwards, it only fits one way we thought of that.

So tell me about the pilot bearing COULD IT CAUSE THIS PROBLEM???????

Thanks, John T

The pilot bearing is more one of those things you should replace when doing a clutch but in reality it doesn't always get done. A bad one can cause chatter.

Its installed in the end of the crankshaft and supports the input shaft and clutch disk when the clutch is disengaged. The unsplined round machined tip of transmission input shaft inserts into it when you bolt up the transmission. Its the main reason you need to use an alignment tool to assemble the clutch and pressure plate assembly cause not only does the input shaft have to go throught the clutch disk but also into the pilot bearing in the end of the crankshaft.

Guess it could cause that problem in an extreme situation but if you took it apart and didn't replace it or damaged it during disassembly then I would consider it unlikely.

Did the transmission slide together easily or did you have to force it with the bellhousing bolts?

Did you compare the thowout bearings to be sure the are the same size? Are you sure your getting enough travel to completly disengage the clutch?

Does it have a CLUTCH BRAKE ?? I AM not up on old buses , Is it a dual disc PULL clutch ??

He did NOT replace the pilot and just now tells me the old clutch acted similar (grinding) which is why he now replaced clutch n plate n throw out and machined flywheel (only AFTER I insisted)

It slides back in easyyyyyyyyyy no forcing or bell housing bolt tightening is ever necessary........

I think theres plenty of travel, when we adjust it up so it really really pushes the fingers a bunch the grinding seems less butttttttt the tranny is still turning

Im tellin him TO REPLACE THE PILOT TOMORROW and I will be there to help. Those detroits are nasty grimy dirty we have to burn our clothes each night lol This is the SEVENTH time hes pulling that big heavy tranny including alternator and drive shaft but hes had so much practice he can pull it in 2 hours.

Ima NOW thinkin the pilot is sticky making the tranny turn even with A GOOD CLUTCH ACTION

Let ya know in a day or so

THANKS John T

No brake and its just a single....

See below, were thinkin pilot is sticky maybe

thanks vet man

John T

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

Check out the info in my post below
JimN

need tocheck splines on headsahft of transmission to be sure disc slides easy on shaft and should not have any grooves or any lube on splines, if so then you will have clutch drivethrough and not a complte release.