i have a 1986 corvette and just installed a 90 model zf-6 transmission and engine. the problem i'm having is when i push in the clutch pedal and shift into first it goes into gear, but i have to rev the engine to about 3500 rpm just to get the car rolling. The same thing happed when i also in reverse. also when i release the clutch pedal in 1, 2, 3, 4 ,5, 6 and reverse the engine doen't stall out it continues to idle which i thought was pretty strange. this afternoon I jacked up rear of the car to see what the rear tires would do in gear. 1'st throught 6th gear would spin, and reverse would spin in reverse which seems normal to me. but the weird part was when i put the transmission in neutral the rear tires would spin slowly i don't know if this is normal. when i push down on the clutch pedal the wheels would roll to a stop, which i think is normal. after i did that test i jack the car back down. i rolled the car out of the garage and outside to the driveway. our driveway is slightly slanted. but the other problem i had is when i put the car in 1st- 6th gear with the engine off the car still wanted to roll back as if the gears aren't catching. i turned on the car and put the car in first gear at idle and car still wanted to roll back, i stepped on the gas and the car slowly accelerated up the drivewayat about 3500 rpm. if you try to drive the vehicle you can get it to go in reverse and 1st gear when you try to shift to second gear it won't shift you get a clashing noise. if anybody know whats going in with the transmisson or cluth please let me know because i can't figure it out.

 

if it does run in gears 1-6 but only above 3500 rpms, it really does sound like the clutch.
to idle in any gear would mean you have no gears at all, or you clutch is blown to poopie. the fact that it moves at all says it is the clutch.

Now when you converted, you had to change the flywheel? What clutch did you install?

Has this thing ever ran normal since you put the trans in? or are you just now finishing up this project?