My C6 which i rebuilt a few days ago is having some problems.

The first problem is it will not shift untill 2500 RPM or when i slitly let off the gas at around 2000rpm. Its got a new modulator valve in it so maybe it needs adjustment? The screw is almost all the way out so i guess the only way to adjust is to screw it in? Is there supposed to be a certain amount of vaccum the manifold is supposed to be giving the modulator?

The second problem is that it will not downshift at very slow speeds, like if i come to a stop sign and dont stop completly. It will down shift if i come to a complete stop. The kickdown cable isnot connected, I dont have a clue what would cause it not to down shift.

 

c-6 needs 21 in vacuum to work.

 

Screw your adjustment on the vacuum modulator inward. You will raise your shift points and you should go down to first gear when you come to a stop. I had the EXACT same problem this summer on my rebuilt C6. I was adjusting it in such minor steps that I didn't notice anything. Don't back it out all the way or you could run into problems. Give it 1-1.5 turns in clockwise. Drive it and see what it does. Get to the point where you see you are making progress, and then fine tune it in or out to suit your shifting needs. Good luck.

 

Thanks...ill go check it for vaccum.

 

21 inches of vacuum would be for a stock engine. I'm running a hefty cam and mine shifts fine with 14-15 inches of vacuum.

 

Mine is shifting with about 10-11" vacuum. It depends on how the modulator is adjusted.

 

If the modulator was changed did the rod behind it get put back in?

 

Did you figure anything out yet?

 

I think ive got it dialed in as good as i can. It still wont shift into 3rd unless i left off the gas, but it now downshifts into lower gear when doing a (rolling stop) at a stop sign. I can manually shift from 1st->2nd->3rd at any rpm.

 

Ok...got a NEW problem (i think).

The trans shifts from 1st->2nd nice and hard(firm shift kit installed) but from 2nd->3rd its not so firm, feels kinda likes it slipping. The rpms only drop 200-300 rpm when it shifts is that correct? Fluid is good and temp is 175 F.