It,s possible you have a miss-matched TO. brg. There are 2 different diapram clutches Chev used. The old style had the fingers near parralel to the flywheel & set back in the pressure plate. It used a long TO. brg.It has about an in. collor. The newer style the fingers protrude forward almost out of the pressure plate. This used a short TO. brg. The groove for the fork is right behind the brg. If these are missmatched it could cause the problem. I take it your pilot brg. or bush. is good.
