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Cruise control components.

rjfguitar

rjfguitar

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My cruise quit working a few months ago and I kind of forgot about it. I remember that I would slowly slow down when it still worked right before it quit which leads me to believe I have a leaky vaccuum line that runs to the cruise setup. I would like to get it fixed because I have a really stiff pedal and it gets tiring on long trips. I don't know much about these early cruise systems and I am asking you guys to educate me on the components and common failure parts so I can understand how it works and can get it fixed.
85K5. Thanks in advance! /forums/images/graemlins/waytogo.gif /forums/images/graemlins/ears.gif
 
Could the stiff pedal contribute to the problem? The servo would have to hold against that pedal pressure as well, perhaps fix the pedal issue at the same time?
 
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Could the stiff pedal contribute to the problem? The servo would have to hold against that pedal pressure as well, perhaps fix the pedal issue at the same time?

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It has a stiff pedal because it has a TV cable attached to the throttle, just like all the other th700 trucks.It's just a little stiff, Just a little stiffer than most vehicles. Thats not the problem. So where is the servo located? What is there for electronics on these systems?
How does the system work? /forums/images/graemlins/ears.gif
 
It is on the rear of the engine on the right side. You can see the cable attached to it running next to the throttle cable.
Any electronis are inside it. Go to your local parts store.
 
Dug this one up instead of starting anew.

rjfguitar, i had the same problem with my cruise control. it still will set, but bleeds off. did you ever solve the problem? if so, what did you do. anyone else feel free to chime in.
 
not exactly, don't have a vac pump with me. but that sounds like a good start.
the speed does not hold but for a second or two, then slows down. the deceleration is not as fast as if you simply let off the throttle. its more like you slowly lift your foot. does that make sense? it seems to me that its trying to maintain speed, but something is not working 100%. i guess i ought to check vac lines again, but i swear i changed them all less than a year ago with no improvements.
 
Components of that system are what...brake switch, wiring/cruise stalk, VSS and Cruise computer, (if '83 or so+) servo, and the vac line. (IIRC)

The vacuum stuff should be easy to check obviously, and if it sets, but doesn't hold, I'd be less suspect of wiring/switches. Vacuum related stuff and VSS would be the two I'd check into, although even then if it sets, VSS shouldn't be a culprit.
 
i noticed that the diaphram/bracket assembly was a bit loose. could that be a culprit? also, it looked like there are two vac lines on the diaphram. one goes through the firewall and up under the dash. i couldn't see where it terminated. do you know, before i start disassembly. the other goes to a t fitting from a port on the tbi and then goes into the firewall on the passenger side, for maybe heater vent control.

how exactly does the cc work? does it physically grab onto the throttle cable, or use the computer to increase fuel and throttle position signals? the more i know, the better off i'll be. thanks for the help.
 
Hmm, don't think I've scanned in the CC section of the manuals. :(

I'm not sure how it all ties together honestly. The VSS is used by the cruise computer to keep the speed constant obviously. Somehow the computer is able to "pull" the throttle to increase it, which would be by vacuum, must be an electric valve or something that opens to allow vacuum to "pull" on the diaphram when required to maintain speed.

Brake switch vents the servo when applied.
 
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