Transmission shifting at wrong time...vacuum problems?
Thread Starter
5th Gear
Joined: Mar 2003
Posts: 5
Likes: 0
From: Milledgeville GA
Transmission shifting at wrong time...vacuum problems?
I've just gotten the motor in my 1971 Corvette rebuilt. One of the things I had done was I put a new camshaft in there. The lifters on it are 462 482 so it's a pretty big one. I have an auto trans on it which seems to be shifting at the wrong time. It will only shift at 3,000 rpm which means you have to be going 50 mph before it will shift into third. I've been told that this has something to do with my camshaft. They also said that I can get a modulator put on there to fix these problems. My headlights are taking awhile to come down too which also leads me to believe that it's all related. How can I fix this? Is it the vacuum not getting enough power or is it the tranny itself? I appreciate the help.
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
The big cam means you have low vacuum. The modulator is looking for higher vacuum, which is causing the funny shifting. Same goes for the headlights.
If you have power brakes, you face another problem! You may need a Hydroboost system for the brakes (or a milder cam)...
If you have power brakes, you face another problem! You may need a Hydroboost system for the brakes (or a milder cam)...
Safety Car
Joined: Jul 2002
Posts: 4,269
Likes: 3
From: St. Charles IL
Cruise-In 5-6-7-8-9-11-12 Veteran
A CI-6 Car Show Winner
You could try a adjustable modulator (they don't cost a lot) You could also do a manual shift valve body. Do you know what kind of vacuum you are making?
