well i just spent a bunch of money on a new adaptor plate, clutch and having my diesel zf5 rebuiilt, but it grinds 3rd gear.
i have brought it back to the shop that rebuilt the tranny and he took it apart and couldn't find anything wrong with it, put new shift fork in and put it back together, still grinds!
now he is saying it could be because of the harmonics difference between the powerstroke v-8 and the cummins 6cyl!
i think this sounds like a load of crap, anyone heard of such a thing?

it is a LUK gold clutch and a ford cummins adaptor plate with hydraulic clutch behind a 91 5.9 6bt

 

I think it's a ZF5 thing...every one I ever drove behind our IDI fleet raked AT LEAST 3rd gear...

Is your throwout making the full stroke? Maybe the pressure plate is staying engaged just enough to make the 2-3 syncro angry? What RPM are you shifting at? IIRC, the "diesel" ZF5 has kind of a weird gear ratio spacing and it fairly picky to shifting RPM especially the 2-3 split, or at least it seemed that way in my experience...

Also, is there anything that might bind the motion up-into 3rd? I recently found out I had insulation/shift boot binding on my G360 that would cause it to jump out of 2nd.

Just thinking out loud on these...

 

this ZF came out of my old Powerstroke, i replaced it because it was grinding in 2nd and popping out of reverse, i have never had a problem with 3rd.
the clutch is definatly disengaging, i actually don't push the pedal all the way to the floor so i don't over flex the diaphram (i have tried pushing the pedal all the way to the floor too, no change).
it doesn't seem to matter what rpm i shift at it grinds unless i double clutch it.
i actually had a small block zf in the truck before, i changed it out for the bigger clutch and closer ratios of the diesel zf, i didn't have a problem with 3rd in that tranny either.

 

if everything seems to be working out just fine when you double clutch then your slave cylinder is not bled properly, air can compress so double clutching will build of up pressure in clutch system, try bleeding it, should be all it is good luck if this helps.

 

nope, clutch has been bled properly
if you just pump the clutch it still grinds, you have to match rpms and pump the clutch. you can shift without using the clutch in the same way with out grinding.

 

its a zf thing. my 94, 3rd would grind ocasionally and then one day i shifted and that was the end. same thing in my 99 with the zf6. so i swapped it for a off the shelf reman and now it grinds all the time. clutch, double clutch, no clutch. but it stops when the fluid temp is above 130* ish. so that "harmonic balance" is a load of crap.