Cruise control
Thread Starter
Racer
Joined: Mar 2009
Posts: 251
Likes: 1
From: Windsor Connecticut
Cruise control
I am helping a buddy of mine who also has a 84 Corvette and we are trying to figure out why the cruise control doesn’t work so far we only check the fuses they seem good I believe but I’m not sure that the brake light switch Hass to be Operating but I didn’t check the brake lights at that time is there anything else that can contribute to the cruise control not working I hope to hear from someone soon
Le Mans Master
Joined: Aug 2017
Posts: 6,940
Likes: 1,490
From: New Jersey
Your suggestion is a waste of time for, and will confuse, the OP because he isn't gong to "hear a click" because nothing happens at the servo by "flicking the switch off and on".
There is no direct "power to the servo". The two solenoids are powered by the Instrument Cluster (which controls the Cruise in 84-89s) as required. It better not "click" when you "flick the switch off and on" because if it did, this would be the vent and vacuum solenoids changing states which would make the servo pull the throttle on with the car standing still. The vent solenoid remains open, and the vacuum solenoid remains closed at all times unless the cruise is actively engaged and operating.
The servo can be checked by energizing the solenoids with an external 12V source and applying an external vacuum source and see if it pulls in and holds. I have checked servos this way, checking for leaks at the solenoid valve seats. If the valve seats are leaking, this malfunction usually shows as "won't hold speed" because the vacuum reserve is bled off through the leak and engine vacuum is too low to apply throttle to increase the speed. The speed falls off.
To the OP: I rarely see feedback on these "cruise control doesn't work" threads where the final solution was posted. In those that do post the solution it is generally related to vacuum supply issues. Hoses, check valves, the vacuum switch under the dash. The cruise in my 9 year old at the time 88 quit working about 2 years after I had purchased the car. A visual inspection revealed that the vacuum supply hose (the small one) had split at the servo nipple. I cut the split end off, reconnected it and cruise worked for another year until I sold the car.
There is no direct "power to the servo". The two solenoids are powered by the Instrument Cluster (which controls the Cruise in 84-89s) as required. It better not "click" when you "flick the switch off and on" because if it did, this would be the vent and vacuum solenoids changing states which would make the servo pull the throttle on with the car standing still. The vent solenoid remains open, and the vacuum solenoid remains closed at all times unless the cruise is actively engaged and operating.
The servo can be checked by energizing the solenoids with an external 12V source and applying an external vacuum source and see if it pulls in and holds. I have checked servos this way, checking for leaks at the solenoid valve seats. If the valve seats are leaking, this malfunction usually shows as "won't hold speed" because the vacuum reserve is bled off through the leak and engine vacuum is too low to apply throttle to increase the speed. The speed falls off.
To the OP: I rarely see feedback on these "cruise control doesn't work" threads where the final solution was posted. In those that do post the solution it is generally related to vacuum supply issues. Hoses, check valves, the vacuum switch under the dash. The cruise in my 9 year old at the time 88 quit working about 2 years after I had purchased the car. A visual inspection revealed that the vacuum supply hose (the small one) had split at the servo nipple. I cut the split end off, reconnected it and cruise worked for another year until I sold the car.
OP: this article hits most of what can be wrong with the system. Mine ended up with the brake NPN transistor in the dash blowing open which as it turns out isn't common but can happen...
Last edited by 84 4+3; Oct 11, 2020 at 07:43 AM.
Safety Car
Joined: Dec 2004
Posts: 3,738
Likes: 217
From: Arizona AZ
Mine ended up being a disconnected vacuum hose........very simple, the hose was disconnected when a new battery was installed...reconnected the vacuum hose and voila.
I'm just throwing this out to look at the obvious. I missed it but found it while photographing the servo unit.
I'm just throwing this out to look at the obvious. I missed it but found it while photographing the servo unit.
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
I have no clicking here in the 85 , but make sure the large hose goes to the pedal is good. and the smaller one goes to the tee then 1 to the ball and one to the heater check valve.That operated the heat as well as the cruise.
