cruise control and guages
07-08-2019, 07:31 AM
#1
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Thread Starter
cruise control and guages
Recently bought a 1980 with a few problems. Both the tach and speedometer needles do not seat back to zero when engine is not running. Tach reads somewhere around 600 rpm and speedo reads 15mph. Speedometer cable now goes from dash directly to transmission. Obviously the cruise control is by-passed.. Should new cables at least correct the speed discrepancy? What about the tach?
Main question is how to determine if cruise control is operational, is that to simply put new cables from dash to transducer, cable to transmission? And if after putting new cables and cruise does not work where does one start to track down the problem?
Main question is how to determine if cruise control is operational, is that to simply put new cables from dash to transducer, cable to transmission? And if after putting new cables and cruise does not work where does one start to track down the problem?
07-09-2019, 07:55 PM
#2
Team Owner
1980 C3 has electric tach and speedo gauges. It doesn't matter what it reads when not running....it's OFF! Check your tach against another tachometer device hooked up to your car. Check your speedo accuracy against the second hand on your watch and mile markers.....or GPS navigator unit in your car.
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rrickerman (07-10-2019)
07-10-2019, 06:55 AM
#4
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Not sure if your 1980 had the resume feature? This manual covers both non resume and resume cruise systems among others.
Thanks again to Willcox Corvette.
Link:https://drive.google.com/file/d/1ykK...7LkTdXbXw/view
Thanks again to Willcox Corvette.
Link:https://drive.google.com/file/d/1ykK...7LkTdXbXw/view
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rrickerman (07-10-2019)
07-10-2019, 12:30 PM
#5
As stated in an earlier post, the tach does not go to zero when ignition turned off. Sometimes the needle floats up a little bit but does not typically go to zero.
On the speedo, I would install new cables to put the cruise control transducer back in the mix. My guess is your speedo needs some refurbishing.
The by-passing of the transducer suggests to me that there is a problem with the transducer and the prior owner did not bother to figure out or fix the problem. It seems clear that there is a problem with the transducer so I would just purchase a re-built transducer instead of trying to diagnose it. I would also purchase new speedo cables as a new ones will be more pliable and easier to fit. Install these, check to make sure the vacuum servo works (apply vacuum by using a Mity Vac or some other hand held vacuum source to see if the servo works and actually moves the carb throttle). Make sure the fuse is good as well. After you install the transducer and new cables, and perform these tests and the cruise still does not work, I would then test the continuity of the engagement button at the end of the turn signal stalk. It is a chore to perform that test and that is why I would save that test for last. Incidentally, if you don't have it already, you should get an authentic GM service manual (often you can find them on Ebay). this manual details all of the tests to diagnose the cruise control.
The 1980 model did not have the resume feature, that feature started in 1981.
I can tell you that there is no better feeling than to do all of this work and then the cruise control works. Very satisfying.
I still think you need to have your speedo refurbished. The needle not returning to zero suggests to me that there is a problem with the speedo. Yes, a chore to remove but to me it is worth it just to make sure all of your gauges work properly.
Hope this helps.
On the speedo, I would install new cables to put the cruise control transducer back in the mix. My guess is your speedo needs some refurbishing.
The by-passing of the transducer suggests to me that there is a problem with the transducer and the prior owner did not bother to figure out or fix the problem. It seems clear that there is a problem with the transducer so I would just purchase a re-built transducer instead of trying to diagnose it. I would also purchase new speedo cables as a new ones will be more pliable and easier to fit. Install these, check to make sure the vacuum servo works (apply vacuum by using a Mity Vac or some other hand held vacuum source to see if the servo works and actually moves the carb throttle). Make sure the fuse is good as well. After you install the transducer and new cables, and perform these tests and the cruise still does not work, I would then test the continuity of the engagement button at the end of the turn signal stalk. It is a chore to perform that test and that is why I would save that test for last. Incidentally, if you don't have it already, you should get an authentic GM service manual (often you can find them on Ebay). this manual details all of the tests to diagnose the cruise control.
The 1980 model did not have the resume feature, that feature started in 1981.
I can tell you that there is no better feeling than to do all of this work and then the cruise control works. Very satisfying.
I still think you need to have your speedo refurbished. The needle not returning to zero suggests to me that there is a problem with the speedo. Yes, a chore to remove but to me it is worth it just to make sure all of your gauges work properly.
Hope this helps.
The following users liked this post:
rrickerman (07-10-2019)