difference between 66-76 & 77-91 C6s

I have a Cheetah valve body for the early c6. Im not exactly sure what year my trans is or how to check but what is the difference between the trans and valve bodies?

If it's an early VB, it should have the manual valve detent in the valve body. That should work in any case and if your using a 72 or later case just remove the detent mounted in the case. However it may need to be used with the pre-77 reverse clutch piston that uses a check ball. 77 and later valve bodies have the check ball inside and not in the reverse piston.

Ok so i install the valve body with the detents and removed the detents out of the trans. I also installed a black stripe modulator. It works and upshifts good but it keeps downshifting from 3rd to 2nd at 1500rpm. Very annoying. It did this before when I had a different auto valve body in it thats why I changed to a manual. Any ideas?

It does have a good manifold vacuum supply??? I had a C4 do similar and guy had it connected to ported vacuum .. Just a thought

Ill try switching to the other vacuum port on the carb but I believe I tried this awhile back when I had the first vb in it and it acted the same way. It upshifts into 3rd fine but wants to downshift way too early. Also it has no kickdown lever on the trans.

There is also differece in the planets and bearings for them, check end play if you have to change these parts out.

Its been awhile since I fixed this but I figured I would update. I switched vacuum ports on the carb and that was the problem. I played with the adjustments on the modulator and it works really nice now. Im very happy it. Previously with the manual vb when you shifted it you needed to use force to shift gears now it shifts manually without much effort and shifts automatically too