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Teach me all about 80's Cruise control systems

rjfguitar

rjfguitar

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The cruise control on my '81 K30 doesn't work, nor does the cruise in my '85K5 anymore. I'd like to get the cruise working again in my K30 CC as I use it every day.

My first question... Does the cruise use the speedometer at all? The speedometer does NOT work in neither of the two trucks in question. This makes me highly suspicious of why the cruise doesn't work, but I thought I'd get some input even before fixing the speedo to learn something new today.:D

How much electronics are involved with these cruise systems?

Are they generally a pain to diagnose or are they simple and easy to fix, generally?

Are the two setups between my '81 an '85 exactly the same and interchangeable? I'm figuring yes, but you never know.

If for some reason my inoperative speedo ISN'T the cause of no worky from the cruise....what would be your best bet on how to start a diagnosis plan and/or what do you think the culprit could be?
 
Not sure when GM stopped using the transducer but if your trucks use them and your speedo isn't working that is probably why your cruise doesn't work either. There should be a cable from your speedo to a transducer box on the fenderwell then another cable from the transducer to the tranny or t-case if 4x4. The transducer will also have an electrical connection on it.
 
the 81 that i had did not have the transducer (think on the fenderwell) i believe it used a VSS on the speedo. my both my 83s, my dads 85 are all the same. so fix the speedo and you should fix the cruise.
 
Sounds good then, I guess I better be getting some new speedo cable.
 
I don't want to modify or update my cruise, I just want the factory setup to work.
 
That's for sure the system you have on the '85, and if you don't have a transducer on the '81 (drivers side fender) then it's what it uses as well.

That article is talking about upgrading the older transducer/"mechanical" stuff to what your '85 (for certain) already has. Therefore the wiring diagrams if accurate, will help you sort through it. Somewhere there is a cruise control diagnosis chart, I'll see if I can find it.

Generally though, VSS on the back of the speedo is what is used to keep the speed, the cruise module is what keeps the system running right, the brake switch turns it off, and the servo is what "pulls" on the throttle.

If the speedo doesn't work, neither does cruise.

Link still works on my post here http://coloradok5.com/forums/showthread.php?t=92247&highlight=cruise+control+diagnosis
 
I have a transducer on my '81, so whats different about this system? How much better is the system on my K5? Does it actually work better on my K5 than this older style?

How should I go about dealing with this transducer setup as far as diagnosing it? Since it appears the speedo cable goes through this transducer, could it be it's fault my speed doesn't work either? I thought I remember the PO saying something about he changed it a couple of times.

Are these transducers a problematic system?
Jan02_0001.jpg
 
my 87 3/4 ton cruise doesnt work but speedo does what should i do...all the vacum stuff is working and it doesnt have the transducer thingy..
 
Not sure what the "problem" was with the transducers, I suspect more than anything the change was just to save money...all the cars went with the exact same system, so parts commonality would save money.

I suppose you could check that the transducer is getting input from the transfer case or transmission, and that it has output as well.

*almost* looks like the transducer has a primitive VSS of some type, (two wires) you'd need to figure out where those go if the speedometer cable seems to work.

'81 could have a VSS on the speedometer, (it existed at the time) but it would seem unlikely in a truck, especially with the wires off of the transducer. Cars did have VSS that early, so it is still a possibility.
 
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im almost positive my 81 didn't have the transducer, unless it was a midyear change :dunno: its been a while since i had that and looked under the hood. anyway...

my buddys 76, while trying to figure out why his speedo didn't work, we found the transducer had input but no output. the little cable did move the speedo. we were just gonna put a longer cable on it and elimate the cruise, ended up selling it before we got that done. not sure if thats a common problem with them, but his was bad.
 
It's been a long time ago but IIRC the wires on the transducer go to the cruise control switch on the brake pedal and the wires from the cruise switch go there as well along with the release vacuum hose.
 
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