c6 shifting late...vacuum pump?

[Kizer]

My c6 is shifting late. It holds the gear alright, I mean it doesn't try to downshift early once it's in the correct gear for given road speed. Vacuum pump?

 

[lindstromjd]

Are your power brakes working? If they are, then I'd say it was your vacuum manifold on the IP that needs adjusting.

 

[Kizer]

Good call lindstromjd. I was just wondering how I was going to test the vacuum pump ... but the brakes are good.
Thank you.

 

[lindstromjd]

Sure. I had a similar problem, but my vacuum pump WAS bad. When I replaced it, the shifting problem didn't go away, so I had to adjust my vacuum thing on the IP. If I remember correctly, towards the firewall is shift sooner, and towards the radiator is shift later. But it's been a while. Just move it in small increments until you get a shift point you like.

 

[franklin2]

Make sure the short hose at the pass side rear of the tranny that goes into the modulator is not cracked also. And all your other vacuum lines are good around the engine.