Ya just gotta laugh sometimes, how fixing things turns out. Thought I would share this with you...

One of the "to be fixed" items on my '81 when I bought it was the inoperative Cruise Control. So here's how it has gone so far...

Step 1: get GM workship manual to lead the way. Ebay and 2 weeks shipping later have GMWSM in hand.

Step 2: Use GMWSM to locate relevant bits. Uh oh. A relevant bit seems to be missing. The servo unit is completely missing from its bracket. Guess that explains why Cruise Control no go.

Step 3: Purchase servo from US based C3 parts supplier, and wait 2 weeks for it to arrive.

Step 4: Instal Servo. Jury rig a linkage from servo to throttle (proper link rod also missing. Anyone know where I can get one from ?) Jump in, go for test run.
Hit Cruise Control.... nothing. Damn.

Step 5. Back to GMWSM to check electrics to Cruise Control Transducer, starting with earth wire check. Out with meter. Check earth wire... and discover there is no   
earth. It is missing altogether. Excellent. Fix earth.

Step 6: Test drive. 50MPH, hit Cruise Control and....
YEEEEHAAAAAA we're off like you wouldn't believe !!! Big smile on face. I obviously have crossed up Cruise Control with Afterburner. Should test more thoroughly though to be sure though. Repeat test from 40 MPH... and WE'RE OFF AGAIN like a cork out of a bottle. Bigger smile.

Find nice long straight. 30MPH and hit Cruise Control...
drops straight to 2nd (auto) and are we on our way or what ~ Oh this is soooooo cool !!! Thought I would just let it go this time and see if it would top out somewhere... but when the speedo pegged at the 85 max it was still going for it. Perhaps something is wrong.

Last test... yes, its a hard job but someone's gotta do it... from dead stopped stationery this time: release foot brake and push cruise control... SHAAAZAMMMM we're on our way again to the top of the speedo !!!

Whilst I obviously have much more exhaustive testing to do before I am able to conclude something is not right, if anyone has experienced this phenomenen before and /or knows how to fix, I'd love to hear from you ! (I think)

For now I have disabled Cruise Control. Wouldn't want to nudge that wee button at an inopportune moment...

You have the vacuum lines crossed.  Switch the one that goes to the servo with the one that goes to the module and I think you will be in business.

You have it now so the servo gets its vacuum signal directly from the engine and not through the module, where the two speedometer cable are attached.  Also, make sure the wire from the back of the speedometer is still there.

 

OH6A38578.1982060185

Dam, I think I'd leave it the way it is for a while.
Sounds like it would be a lot of fun on the Interstate.
And you could tell the nice police officer your vacuum lines must be crossed. I'm sure he's never heard that one before.

Thanx for that, will chek it out wen I get my neck brace off

Ahh well another "round to it" jobbie just completed... whats a couple of years or so between talking about it and doing something about it matter

So it wasn't crossed lines of course (that would have been way too easy to fix now wouldn't it ?) so much to the disgust of my wife the transducer came out and onto the dining table for the day (women have no sense of priority do they )

A rather good article I found on the net by Theo Law about stripping down C3 Cruise Controls was my bible, and was a very good one too !   To cut to the chase, it was full of years of dirt dust and grime and needed a very very good clean and blow out. The principal culprit was that the speedo cable from the gear box drives a magnetic disc in the transducer, which has a second disc paralleled against it with a wee air gap between them. The rotation of the first disc causes the second disc to try and rotate with it (due to the magnetics), but the second disc has a spring holding it so that it only actually turns as far as it can against the spring tension. Thus the arc through which the second disc has turned is directly proportional to the speed the first disc is rotating. The second disc then modulates the amount of vacuum to the servo as it shifts on its arc due to vehicle speed change.

Well that's how it is supposed to happen. In my case where there was supposed to be an air gap between the discs I has sludge. So the second disc was just being driven to the full end of its arc irrespective of speed due to sludge friction, and could not drop back at all to reduce vacuum to the servo. So the servo just stayed in maximum suck back as a result, giving rise to after burner syndrome.

All is good now, in fact I am very impressed with its operation. A bonus is that the input cable has a gear on it which drives a second gear to which the output cable to the speedo is connected. In cleaning out and lubricating these gears my speedo needle wobble all but disappeared !

Dismantling the transducer is a little fiddly and does have some traps, but armed with good info is not difficult. Contact me if you would like some pointers !   (before you open it up)

Nice to get those "Round tuits" done.

Good job, Chris!!
I've cleaned many of those transducers...hard to believe all of the crap that can make it's way into them, but it does. Then again, a lot of the ones I've had apart were so rusted up they weren't worth fixing.

Congrats on the repair!!

CeeDee talked about car parts all over the dining table and the reaction which followed.  Imagine the reaction when parts are found in the dish washer?  Oh my!  It was about as bad as greasy rags in the washing machine.  My wife does have a great sense of humor though.

Greasy rags in the washer Ive done, never been brave enough to clean parts in the dish washer though.

Glad to hear you got yours working.  That is on my to do list, but not quite to the top.

Ran all my light fixtures, side markers, tail lights, etc., thru the dishwasher.  Had to do it twice to get the gunk out of it.

Wife called at work and asked if she needed to pull them out and drain them as some had turned upside down (or downside up in this case) and filled with water.  She's pretty tolerant of me since she enjoys the benefits of the tops being off...and nothing I do would really surprise her!
dnv2008-02-13 07:43:13