.

What do you have for total clutch pack thickness? New should be 2.750". Minimum is 2.485"
There should not be any perceptible axial or radial movement of the bevel gear shaft. Axial movement (right to left) will affect the steering clutch clamping.

You have done the obvious, but you did not say if you have service book and have the linkage the correct lengths. The other thing in my mind is if the springs are not from Cat, are they the right strength. The service book give pounds at given height.

As a surprise to me had set of spring just give up. New tractor to me had several 100 hour use. In one afternoon went from working to not.

Cat service books say to add the additional plates. As poor farmer I have added more than one without any problems.

Bevel gear bearing adjustment is important, again follow the service book.

I maybe had 15 D7C and I all time use 10 discs and 10 plates and had 2 7/8 inchs tickness and maybe you have the wrong drum or wrong studs the D6 use 12 plates and 12 discs and use't the same drum.

.