I thought it was a vacuum leak but it was the cruise control! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Nickelcharlie · 01-15-2019, 06:57 PM

Any suggestions what might be causing my cruise control not to engage?

With the engine running and in park what I thought to be a vacuum leak turned out to be the cruise control sucking the rod that goes to the carburetor back thus causing a very high idle. I removed the rod that is connected to the cruise control servo at the carb and my idle dropped back to normal speed. So I ordered a rebuilt cruise control servo and replaced the old one with the rebuilt one. Engine idle speed now stays at normal idle speed. However, my cruise does not work. Any suggestions on what might be causing the cruise control not to engage? Thanks for your help!

andyh1956 · 01-16-2019, 05:50 PM

Do you have a wiring diagram for the cruze for your truck?

Nickelcharlie · 01-16-2019, 09:36 PM

I do not have a wiring diagram. I'll do a search and see if I can find one for the cruise control Thanks, for the reply.

**Wgesnerjr** · 01-17-2019, 07:44 AM

Some Cruise Control units utilized a vacuum release at the brake pedal. check to see if the may be hung open, causing a leak.

You can also try disconnecting the wiring harness to se if it returns to normal. That would point you towards an electrical issue. if not disconnect the vacuum and look for normal. This way you can isolate the issue to electrical or vacuum.

Nickelcharlie · 01-17-2019, 01:36 PM

Thanks Wgesnerjr, I'll look and see about the brake switch. I do have a hose coming from the cruise control going down into the firewall, I'll check it out!

**hatzie** · 01-18-2019, 02:18 PM

The CruiseMaster and Cruise III training manuals are posted in the manuals thread.
The 1979 service manual has a pretty decent section on CruiseMaster too.
There is a vacuum switch on the brake pedal on at least one of those systems.

01-15-2019, 06:57 PM	#1
Nickelcharlie Registered User Join Date: Sep 2016 Location: Cleburne, Texas Posts: 83	I thought it was a vacuum leak but it was the cruise control! Any suggestions what might be causing my cruise control not to engage? With the engine running and in park what I thought to be a vacuum leak turned out to be the cruise control sucking the rod that goes to the carburetor back thus causing a very high idle. I removed the rod that is connected to the cruise control servo at the carb and my idle dropped back to normal speed. So I ordered a rebuilt cruise control servo and replaced the old one with the rebuilt one. Engine idle speed now stays at normal idle speed. However, my cruise does not work. Any suggestions on what might be causing the cruise control not to engage? Thanks for your help!

01-16-2019, 05:50 PM	#2
andyh1956 Registered User Join Date: Mar 2010 Location: thomastown mississippi Posts: 1,261	Re: I thought it was a vacuum leak but it was the cruise control! Do you have a wiring diagram for the cruze for your truck?

01-16-2019, 09:36 PM	#3
Nickelcharlie Registered User Join Date: Sep 2016 Location: Cleburne, Texas Posts: 83	Re: I thought it was a vacuum leak but it was the cruise control! I do not have a wiring diagram. I'll do a search and see if I can find one for the cruise control Thanks, for the reply. Last edited by Nickelcharlie; 01-17-2019 at 01:37 PM.

01-17-2019, 07:44 AM	#4
Wgesnerjr Senior Member Join Date: Jun 2015 Location: Atlanta, GA. Posts: 737	Re: I thought it was a vacuum leak but it was the cruise control! Some Cruise Control units utilized a vacuum release at the brake pedal. check to see if the may be hung open, causing a leak. You can also try disconnecting the wiring harness to se if it returns to normal. That would point you towards an electrical issue. if not disconnect the vacuum and look for normal. This way you can isolate the issue to electrical or vacuum. __________________ Jay Gesner Atlanta, GA 1985 C10 Long Bed 4X2 LS 5.3, 4L60E Father/Daughter Project

01-17-2019, 01:36 PM	#5
Nickelcharlie Registered User Join Date: Sep 2016 Location: Cleburne, Texas Posts: 83	Re: I thought it was a vacuum leak but it was the cruise control! Thanks Wgesnerjr, I'll look and see about the brake switch. I do have a hose coming from the cruise control going down into the firewall, I'll check it out!

01-18-2019, 02:18 PM	#6
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: I thought it was a vacuum leak but it was the cruise control! The CruiseMaster and Cruise III training manuals are posted in the manuals thread. The 1979 service manual has a pretty decent section on CruiseMaster too. There is a vacuum switch on the brake pedal on at least one of those systems. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.



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