Transmission shifting at wrong time...vacuum problem?

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Aug 26, 2004 | 07:33 PM

Harpe

Thread Starter

5th Gear

Joined: Mar 2003

Posts: 5

Likes: 0

From: Milledgeville GA

Transmission shifting at wrong time...vacuum problem?

I have just gotten my motor rebuilt on my 1971 Corvette and one of the things that I got done to it is a new 462 482 ratio camshaft. I have a auto trans and have noticed that the only time it shifts is at 3,000 rpm. This means that you have to be doing 50 m.p.h. for it to shift into third. I've been told that it has something to with the vacuum. They said that because of the new camshaft, I need to get a modulator to run the vacuum system. They said that this will fix it. I've also had problems with my headlights not going down right away when you turn them off since having the motor worked on. Could this all be related or is it just the transmission? I appreciate the help.

Aug 26, 2004 | 08:23 PM

TedG

Safety Car

Joined: Feb 1999

Posts: 4,977

Likes: 10

From: Reno NV

Quote:

Originally Posted by Harpe

Even though this is the C6 forum, let me try to answer your question. Vacuum most certainly can cause these problems. I am not sure if your headlights are vacuum operated, but there is a good chance they are. A camshaft can cause low vacuum but usually at idle(unless there is a huge overlap). the tranny will not shift properly if there is low vacuum, also your power brakes will be hard to apply. If it is a cam it must be a whopper. Have your vacuum checked by a knowledgeable shop and make sure your PCV valve is installed correctly. I am sure the guys on the C3 forum can be of more help.

Aug 26, 2004 | 09:26 PM

BigJoe

Race Director

Joined: Jun 2000

Posts: 13,733

Likes: 66

From: Hurst, TX USA

The lights are vacuum operated for sure, so you have two vacuum systems acting up. I think you need that modulator if it allows the vacuum to build up to normal levels.

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