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Common reasons for no cruise control?!


speedyquest
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Hey guys, I just aquired a 1988 durban widebody with an auto tranny. While driving it home i realized the cruise control doesn't work. Does anyone have any suggestions as to what to check, fix, etc? I'm guessing there is a common reason for it to stop working and someone will have a good set of guesses for me.

 

Thanks for your time

 

Allen

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check to make sure the pedals arent sagging enough that it wont engage. While driving lift up on either one with your toe while trying to engage it. This is what fixed mine. Bill "coldscrip" also has figured out that sometimes it has something to do with a bushing or something on the pedal? PM him for more info. I dont know any of the details on this fix.
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There are basically five areas that are notorious for causing the cruise control not to work:

 

1 - Fuse blown for some reason - check this by turning the cruise control (CC) ON at the right stalk on the steering column. Is there a orange square light lite up? If so the fuse is OK. If not then the fuse is blown.

 

2 - The vacuum tubing to the CC actuator/AC vacuum actuators has a hole/cracks in it, it is blown off of the nipple under the gang of three nipples on the TB or one of the ttwo plastic check valves is missing, installed backwards or is leaking.

 

A - Check the Crusie Control/AC actuator tubing run for damage and replace it all, cuz it's probably dry and crusty from age and engine house heat. Make sure that you reinstall the plastic check valves with the enbossed arrows pointing back to the intake manifold.

 

B - There should be a check valve installed in the tubing between the actuator and the vacuum switch and another between the vacuum volume air can and the tee going into the vacuum "header" tubing coming from the intake manifold nipple. See the below picture. The two check valves are the upper most white things in the vacuum tubing - on one of 'em you can even see the arrow

 

http://i1032.photobucket.com/albums/a409/Starionpilot/Starion%20Front%20Spoiler%20Damage/Cruisecontrolcheckvalvelocations.jpg

 

 

C - Remove the actuator and disassemble it. Look where the vacuum tubing attaches to the actuator tubing nipple. Is that nipple there? Many times it is broken off during removal/installatrion of the air filter cannister. If it's missing you can drill out the broken nipple using a 5/32" drill bit. Get some 5/32" brass tubing and cut a 1" piece off and JB weld it in the drilled hole.

 

Another thing that happens inside the actuator is it's foam air filter has disintagrated over time and the crud has settled out on the actuactors electrical contacts or a piece of it is holding the actuator's vacuum valves open or shut. The actuator is fairly easy to disassemble & clean. Get fish aquarium foam air filter from a pet shop and cut a piece to exactly fit in the cavity after everything is cleaned. Also check the bell shaped diaphram for holes, cracking or cuts. If you have holes, cracking or cuts you have to get a new actuator with a good diaphram. Reassemble and reinstall the actuator.

 

4 - Look at the clutch/brake pedal assembles. There is a plastic button insert that the clutch CC switch pin contacts and the same thing for the brake switch. See the below picture of the clutch pedal assembly - it's the yellowish plastic "button." The same button is located on the brake pedal assembly in the same place.

 

http://i1032.photobucket.com/albums/a409/Starionpilot/Starion%20Front%20Spoiler%20Damage/clutchpedalassembly.jpg

 

These "buttons" get worn out and the clutch & brake switches pins stay fully extended, with the pedals at rest, telling the cruise control (CC) computer that the clutch is being shifted (pedal is depressed) or the brakes are being applied. Consequently the CC computer will not engage the CC. You can buy these buttons from PQ on his i-x.net SOS Manuals catalog.

 

You can buy the 5/32" vacuum tubing from NAPA. The Part number is H459. You might also check the rest of the rats nest of vacuum tubing in the engine house for cracks brittlenes or holes. You should replace it piece by piece, cuz you will NEVER remember where each piece of tubing goes if you remove the complete rats nest at one time. Other guys have used other 5/32" vacuum tubing but I have had excellent luck with the NAPA tubing.

 

5 - Even if the vacuum pump is FUBAR, you will have cruise control at a steady speed (provided the rest of the system is sat) and the vacuum tubing to the vacuum pump is intact and hooked up to the vacuum pump.

 

Here is a picture of the vacuum pump location by the drivers side head lite assembly

 

http://i1032.photobucket.com/albums/a409/Starionpilot/Starion%20Front%20Spoiler%20Damage/Cruisecontrolvacuumpumplocation.jpg

 

and here is a picture of the vacuum tubing coming out of the vacuum pump on it's way to the vacuum actuator. Sorry about the focus - but you get the point. ...

 

http://i1032.photobucket.com/albums/a409/Starionpilot/Starion%20Front%20Spoiler%20Damage/Cruisecontrolvacuumpumptubing.jpg

 

For What It's Worth.

 

KEN

Edited by Starfighterpilot
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