I have a C6 that acts weird occasionally. It will shift great for days then all of sudden one day it will stay in 1st longer than normal then skip 2nd and go to 3rd. When it's acting this way if I stop it downshifts to 1st. Now from a standstill if I accelerate moderately to hard it will roll forward in 1st and almost immediately shift into 2nd at less than 5 miles an hour, it will then shift normally into 3rd. When it's doing this sometimes it will not downshift into 1st when I stop but instead will downshift and take off in 2nd. Now I can stop, put it in reverse or park then go back to drive and it will shift normally for weeks or day before doing the weird shifting.

The transmission has been completely rebuilt. I have not tried to adjust the vacuum modulator because the problem is intermittent.

Does anyone have any idea why it would do this?

 

2nd gear starts is usually a governor problem and the other issues can be governor related as well. If it gets worse you might have to remove the governor and clean it, the little valve inside can collect trash and this can make it a little sticky.

You may be able to free it up by adding a additive like Lubegard.

 

Thanks. Any ideas how a rebuilt tranny could get a sticky governor? I had an older gentleman with a good reputation rebuild the tranny. I know no one is perfect.

 

I answered this in a different forum. Minute particles of metal can embed themselves in an aluminum body. It doesn't take much to hang up a valve.

 

Stuart, I tried your trick yesterday.

"Some times you can get it to move by yourself. Without taking it apart. Take off using minimum throttle until it shifts into high. Pull the lever into Low then back to Drive. Do this several times."

It worked. This morning it shifted well but this afternoon it skipped 2nd a few times. I tried your trick again and it fixed it. I will stop by and pick some "Lube Guard" and add it. I'll see what happens this week.

 

I've had two C6 transmissions that, with sticky govenors, would become reluctant to downshift into 1st as you stopped, & then take off in 2nd.

Driving quickly in reverse for a minute or so, flushes the tailshaft housing (& the governor) with fluid. This fixed the problem in both cases.

 

I got the truck back from the transmission shop today. They couldn't find anything wrong with the governor. They thought it was something in the valve body. They couldn't find anything wrong with it. They swapped in another valve body and the transmission worked correctly. So far it's working great. They could not figure out what went wrong in the rebuilt valve body I bought from Broader Performance. I'll speak to Broader about it tomorrow. I did speak with Jay B. earlier in the week and he was very helpful. Thanks for everyone's input.