OT 671 Detroit Clutch

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

John T,

Is that a double disc clutch with a floater plate between the two discs? I am suspecting that it is, and if so there will be a ring on the pressure plate that has notches in it. One of those notches will have locking tab bolted into it with a 5/16 capscrew. Remove the bolt and using a fairly heavy hammer and punch, rotate the notched ring one way or the other until the clutch disengages when the pedal is depressed. It won't take much, maybe three or four notches. If you go the wrong way the first time, your problem will get noticeably worse. Wish I could remember which way to go with this, but alas, it's been a long time.

If you don't have the double disc clutch, I would check for wear on the clutch release fork and ball where it pivots.

Hope this helps.

don't ask how I know,, but if the facing is installed backward this can be the problem Bill

pilot bearing bad?

THANKS GANG, I help others here when I can and appreciate some help for my buddy...........

Its NOT a double disk and YES its on correct NOT backwards as it only fits one way. Guys on another board are thinkin the Pilot Bearing (which he DID NOT replace although had same problem with old clutch) is bad/sticky causing the shaft to still turn even when clutch is released. What say you ???????????

John T

One thing it might be is if the input shaft has a lot of wear it can cause the clutch disc to hang and not slide,which might not let it disengage.

Also if every part of the linkage is worn out,you maybe have lost all the effective use of the pedal to wear in the linkage.So when you start pushing the pedal,it should right then go to the forks on the pressure plate and push them for every bit that you push the pedal down.Any wasted motion could be why its not releasing.If there is an arm on the side of the bellhousing you can get to that releases the clutch,while somebody holds down the pedal,see if you can move the lever more,and if you can,are you able to shift it.

Hello John T,
Is the clutch push type or pull type. they are not adjusted the same way. Most 6/71 I have worked on had the spicer pull type angle spring clutch. Initial adjustment between the release bearing and the transmission input shaft cover plate is 1/2". Free travel of the cluch pedal should be 1 1/2 to 2 in". What happens is that the cluch free travel is adjusted by someone that is not familiar with the right way to do it.
They used the linkage and not the clutch adjusting ring. That can drive you nuts.
Give me what type of clutch you have and i'll give you ther proper procedure to adjust it.
My e-mail is open.
Guido.

Hello John,

You should not have adjusted the fingers on the clutch, these are set with a special jig when it's rebuilt. These are critical that they are all the same heighth when on the jig for adjusting.

Second, there should only be 1/8" clearence between the throw out bearing and the clutch fork fingers. This can easily be checked with an 1/8 brazing rod. Then you adjust your clutch pedal free play with the linkage. Free play should measure 3/4".

Is this a heavy duty pull type clutch or a lighter duty push type?
If it's a pull type, does it have a clutch brake? Did it have one and now it's gone?
That's the first thingthat springs to my mind. The second thing is the pilot bearing. The third thing is the splines...

Rod