Transmission Advice Please

[Richard2112]

I could sure use some advice on a noise (sort of a grinding sound) coming from the trans.

I am installing an NV4500 in place of an SM465. I have used the cast iron bell housing from the SM465 and drilled and bolted the bell housing to the NV case so all internals within the bell housing should be the same. That geometry shouldn't have changed much with the exception of a reground flywheel and a thicker clutch disc.

The NV is rebuilt stem to stern and the input rotates freely, all the gears engage smoothly...while the truck isn't running. When I start the truck the four forward gears and reverse engage easily enough but 5th won't engage.

Moreover, If I start the truck while it is in gear and move the clutch pedal a bit up or down, the grinding noise will occur.

I do not have a drive shaft connected and there is no drag on the transmission yoke. It spins freely in all gears. There appears to be some clutch drag as the yoke will spin in neutral also but again, there's no drag induced at the yoke so I suspect that even slight clutch contact will cause the input to turn and consequently the output yoke will spin.

With my tunnel cover removed, I can see the yoke turning while in neutral and I can actually reach down an grab it and it will stop turning. This is why I think that some slight clutch contact is causing the shafts inside to rotate while in neutral.

Does there need to be some drag on the output yoke to control the spinning motion of the internal shafts? Could this be why there is a grinding sound when the clutch pedal is lifted and depressed slightly?

I have had the flywheel ground (not turned), installed a new bronze pilot seemed to go in nice/tight/straight, installed new clutch disc and T/O bearing.

Just not sure why it would make a grinding sound when the clutch is moved. Could sure use some advice. Thank you