ZF5 makes grinding clunking sound

[aaron1976]

I have a 1990 f250 7.3 with the zf5 trans.

When it is idling and in nuetral without the clutch pedal pushed in the tranny makes a clunking noise and sort of a grinding noise. It goes away when the clutch pedal is pushed in and the trans is not spinning. The trans shifts great, no grinding and feels solid. The trans has plenty of fluid. I don't notice anything odd when I am driving it.

Any body have any ideas?

 

[93f250idi]

maybe a throw out bearing??? not sure if a 87 had one but maybe a dual mass flywheel coming apart??? just some sugguestions