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Cruise control Vacuum

larry bud

Well-known member
Joined
Jan 21, 2002
Messages
234
Location
Rochester, MI
Corvette
1986 "Speed Yellow" Coupe
I'm hoping I finally tracked down a vacuum leak that I've had FOREVER....

There are 2 vacuum lines going into the cruise control module. If I pull a vacuum on one of them, blocking the other, the module should hold a vacuum, correct?

If I block both holes and push in and out on the module, I shouldn't be hearing any air coming through, right?

If yes to both of these, I found the leak!

In addition, for a test, I disconnected the two hoses that go to the cruise control module and connected them to each other (one happens to fit nicely into the other). Once I readjusted my idle, the thing idled like a rock.
 

jmccloud

Well-known member
Joined
Feb 1, 2003
Messages
694
Location
Maryland
Corvette
1995 White Coupe LT-1 Auto
vacuum leak

Sounds like the diaphragm in the controller is broken.
 

86PACER

Well-known member
Joined
Dec 31, 2002
Messages
182
Location
CA
Corvette
1986 Pace Car
I'm hoping I finally tracked down a vacuum leak that I've had FOREVER....

There are 2 vacuum lines going into the cruise control module. If I pull a vacuum on one of them, blocking the other, the module should hold a vacuum, correct?

If I block both holes and push in and out on the module, I shouldn't be hearing any air coming through, right?

If yes to both of these, I found the leak!

Wrong. To test the cruise servo, you must remove it's plastic back cover where the electical connector goes. The way you are testing it will always give you a false bad test. Remove the small torx screws, then the back cover. Now you will find a "button" looking thing. With one hand press in the cruise diaphram and hold it there. Now with the other hand press and hold this "button" and release the diaphram. The cruise diaphram should hold sucked in and very slowly release if the servo is good while you finger is pressing the "button". When you release, the cruise servo should also immediately release.

For more see this step by step guide with pictures.

http://www.corvettefever.com/howto/82001/

Is you cruise control working?

Here's how the cruise vaccum is routed.

 

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