Cruise control
Race Director
Joined: Nov 2006
Posts: 13,335
Likes: 7,904
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Old worn diaphragm? Miss adjusted?
it's very, very old. Lots of things come to mind.
GM NEVER thought it would last this long.
Perhaps try adjusting it first. These early cruise controls never worked as well as the modern ones do now.
it's very, very old. Lots of things come to mind.
GM NEVER thought it would last this long.
Perhaps try adjusting it first. These early cruise controls never worked as well as the modern ones do now.
Safety Car
Joined: Oct 2007
Posts: 4,394
Likes: 1,775
From: Seattle Area Washington
It sounds like you are experiencing a "Surging" issue...
A out of an adjustment servo rod can cause this, the rod adjustment should be tight between servo and carb stud but not tight enough to increase hot curb idle speed
Test run at 50mph...
Another thing to test...
Disconnect the rod from the servo to carb...
Remove the vacuum line from the back of the servo and pull a vacuum, 10-15" is plenty.
If the vacuum drops more than 4" of vacuum in one minute your servo is defective.
A out of an adjustment servo rod can cause this, the rod adjustment should be tight between servo and carb stud but not tight enough to increase hot curb idle speed
Test run at 50mph...
Another thing to test...
Disconnect the rod from the servo to carb...
Remove the vacuum line from the back of the servo and pull a vacuum, 10-15" is plenty.
If the vacuum drops more than 4" of vacuum in one minute your servo is defective.
Race Director
Joined: Nov 2006
Posts: 13,335
Likes: 7,904
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
The servo, that's the diaphragm I mentioned. I think the way it's explained above is a better way of saying it, but pretty much the same as what I said. Cruise control is really nice when it works well.
best of luck to you.
best of luck to you.
Burning Brakes
Joined: Dec 2011
Posts: 844
Likes: 6
From: Fort Wayne, IN
Currently working on LS swapping my 77, and when I pulled the engine and trans from my old 2002 Avalanche, I also pulled the cruise control wiring, module, and stalk controls.
I'm still working on the wiring since I've had to mod the engine harness, and I'm also rewiring the dash as well to upgrade to the avalanche interior fuse box. I have it all down on paper, and i'm currently in the process of implementing it. Once I do get it done, I'll make my own step by step post and probably a tiktok video to document how I did it.
I'm still working on the wiring since I've had to mod the engine harness, and I'm also rewiring the dash as well to upgrade to the avalanche interior fuse box. I have it all down on paper, and i'm currently in the process of implementing it. Once I do get it done, I'll make my own step by step post and probably a tiktok video to document how I did it.
Race Director
Joined: Nov 2006
Posts: 13,335
Likes: 7,904
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
And how does any of that have anything to do with the original poster of this thread?
I don't do Tic Tok. So maybe I'll miss it.
But this thread started with issues with factory stock cruise control.
Nothing at all to do with a complete rewire for a non standard engine.
I don't do Tic Tok. So maybe I'll miss it.
But this thread started with issues with factory stock cruise control.
Nothing at all to do with a complete rewire for a non standard engine.
Burning Brakes
Joined: Dec 2011
Posts: 844
Likes: 6
From: Fort Wayne, IN
When you stated "These early cruise controls never worked as well as the modern ones do now.", I was just excited to spread the knowledge that I worked out of adding a newer stock GM unit to our cars. Something that I haven't seen very many people do. I was throwing out an option for a more reliable cruise control.....granted it's for an LS swap which is my first one, so I'm excited about it.
*Edit* it looks like my original reply, went to a different thread than I originally wrote it for. I meant to post it on the more recent cruise control thread....I'm not sure why it went to this one. I'm an idiot sometimes...lol
*Edit* it looks like my original reply, went to a different thread than I originally wrote it for. I meant to post it on the more recent cruise control thread....I'm not sure why it went to this one. I'm an idiot sometimes...lol
Last edited by TurboStitchCW; Oct 22, 2024 at 06:39 PM.
Race Director
Joined: Nov 2006
Posts: 13,335
Likes: 7,904
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
No, your not an idiot, probably got caught out by the forums practice of putting a related thread on the end of the thread your reading.
Ya gotta really watch out for that!
And I even seen your reply to the later thread. But at the end of the day, the BEST thing for you to do is START a new thread. And then share your information.
And then in years to come perhaps people will find your information
Ya gotta really watch out for that!
And I even seen your reply to the later thread. But at the end of the day, the BEST thing for you to do is START a new thread. And then share your information.
And then in years to come perhaps people will find your information
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Race Director
Joined: Oct 2000
Posts: 17,102
Likes: 7
From: Fair Oaks, OK
Do you know if the cruise control transducer is in good serviceable condition?
I have no idea how to test or verify, but I know the cruise on my '79 was similar to what you're describing. I found the internals of my transducer were in not-so-great shape.
I have no idea how to test or verify, but I know the cruise on my '79 was similar to what you're describing. I found the internals of my transducer were in not-so-great shape.
Racer
Joined: Jul 2011
Posts: 261
Likes: 73
From: Los Angeles County
I'm very surprised the option isn't there. Even if you don't like it, someone else may want it. Not everyone likes AC. I'm glad it wasn't built according to their likes and dislikes.
Last edited by twoweeled; May 9, 2025 at 10:39 AM.
Cruising
Joined: Apr 2025
Posts: 11
Likes: 4
Honestly, I’m not too surprised. While adaptive cruise control is a great feature, not all car manufacturers prioritize it in every model. It could be that the 2026 model is focused on other aspects or features that they think are more important for their target market. It’s definitely a bummer for those who expected it, though!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Old GM cruise control heads get dirty inside. It has a friction disc inside and that gets dirty and looses speed stability. There is also a calibrated orifice inside which can become dirty/clogged. Clean it out, also. If you don't have a vacuum reservoir or yours is leaky, this can be a problem, as well.
Removing the control head, opening it up and cleaning it is not a big deal for a decent DIY'er. Good luck.
Removing the control head, opening it up and cleaning it is not a big deal for a decent DIY'er. Good luck.