cruise control problem
Thread Starter
Instructor
Joined: Dec 2004
Posts: 198
Likes: 0
From: Newmarket Ontario
cruise control problem
I have a 1979 automatic with a L48 engine. Problem is when I set the cruise button it acclerates flat out. I have gone over the shop manual on trouble shooting the symptom but the manual does not mention anything about that issue. Any ideas what is causing this? 
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
My '79 did the same thing. I solved the problem in the most efficient manner...I tore out the cruise control junk and put it in a box 
Now there's more space under the hood!
Now there's more space under the hood!
Burning Brakes
Joined: Feb 2005
Posts: 1,007
Likes: 0
From: Shoshone Idaho
Be careful, I had something like that happen to me in a older car on a windy mountain road, but I could not take it out of cruise control, and had no place to pole over 
After that I won't use cruise in older cars 
It wound up that a new fuse fixed the problem, but I still won't trust cruise in older cars.
After that I won't use cruise in older cars It wound up that a new fuse fixed the problem, but I still won't trust cruise in older cars.
Burning Brakes
Joined: Sep 2002
Posts: 1,179
Likes: 3
From: SF East Bay CA
Your sruise is vacume operated.. I would check the druise unit first and all the vacuum lines from the cruise unit to the bellows. Sounds like a unit or vacuum problem. I have a 79 also, but I ended up removing it when I went to TPI. I think the cc units run a bit over $100.. check your vacuum lines first.
Melting Slicks
Joined: Mar 2003
Posts: 2,512
Likes: 49
From: Franklin IN
Checking out a cruise system on this cars is fairly easy. On my wifes 79 the bone heads a CNV Corvettes in Phoniex ripped the controls off the car but left all the wiring and vacuum lines in place. So I checked one line at a time using a small vacuum pump. On her 79 it only has 2 wires to connect to the cruise unit so I wired a light bulb in the circut and taped it to the windshield. When I pressed the button for cruise while driving the light came on. From the discription you gave you need a new/rebuilt control unit I got one from my local parts store for about 79.00. I'd bet that will clear up your problems. An assembly manual sure makes figuring out which line goes where much easier.
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
actually, i think that was an RPO option for 79. GM was doing some experimenting with launch controls for the street/strip crowd. you may have one of the rare 79's with that factory option installed. 
