1979 erratic cruise control
11-27-2005, 11:43 AM
#1
Racer
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Location: Fairfield Texas
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1979 erratic cruise control
What I have here is a 15000 mile 79 L48 automatic that will not
maintain a steady speed when cruise control is engaged. After the
cruise is engaged it will accelerate 3 to 5 miles an hour then drop back
to set speed then accelerate again then drop back and on and on like
this.When the cruise is not on I can hold a steady speed and the
speedometer needle is rock steady so appearently the problem is not
one of the speedometer cables binding in the case. Just thought perhaps someone else had this problem in the past and could supply
an easy fix. ("Easy" on a Corvette,NOT likely )
Thanks,Dennis
maintain a steady speed when cruise control is engaged. After the
cruise is engaged it will accelerate 3 to 5 miles an hour then drop back
to set speed then accelerate again then drop back and on and on like
this.When the cruise is not on I can hold a steady speed and the
speedometer needle is rock steady so appearently the problem is not
one of the speedometer cables binding in the case. Just thought perhaps someone else had this problem in the past and could supply
an easy fix. ("Easy" on a Corvette,NOT likely )
Thanks,Dennis
11-27-2005, 01:14 PM
#2
Heel & Toe
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I repaired the cruise on my 79. It wouldnt engage, different than your problem. I would suspect the cruise control transducer, mounted on the left side of eng compt. Seems to be the brains of the whole system. Not hard to change. cost was around 70 dol.
11-27-2005, 02:34 PM
#3
Safety Car
Hi, I think there is a certain amount of adjustibility to the transducer but as usual I am not positive,,, I usta know more but I've hit one tooo many trees. Peace,,,Moosie 
11-27-2005, 03:36 PM
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chevylit; You might try to take any slack out of the cable that goes from the servo to the carb.. If there is too much slack in this cable the cruise will hunt. They usually have an ajustable sleeve with threads and a nut to lock it in place on the end of the cable. There should be nearly 0 play in this cable. Be sure your choke is warmed up and you are setting on your fast idle adjustment screw before you try to adjust it. Hope this helps. 
11-27-2005, 04:09 PM
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Racer
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Took Terry82s advice and checked vac lines,sure enough the line
from manifold to transducer will not hold vac.Will go to vacuum hose
store first thing in morning for new piece of hose. Then I read OldMOs
suggestion about too much slack in rod from servo to carb and sure
enough again,mine has between 1/16 and 1/8 inch slack. Will fix these
two problems and I bet'cha I am cruise'n again.
Thanks You Guys, Dennis
from manifold to transducer will not hold vac.Will go to vacuum hose
store first thing in morning for new piece of hose. Then I read OldMOs
suggestion about too much slack in rod from servo to carb and sure
enough again,mine has between 1/16 and 1/8 inch slack. Will fix these
two problems and I bet'cha I am cruise'n again.
Thanks You Guys, Dennis
