G Man

I'm having trouble with my cruise control. My car is a 81' U.S. auto. I looked in the archives before posting with no luck. When I engage the cruise control the car accelerates like I have just floored the acclerator pedal. Whoah, hold on! I have to turn off the cruise or hit the brakes to disengage. Any advice as to where I should begin looking for the culprit.

SharkSkin

Mine was completely dead. I revived it to perfect operation by using carb cleaner to clean the back side of the PCB(carefully... don't get that stuff on the component side!) and re-soldered all of the connections. I did this only after disconnecting the plug, jacking up the car so I could test the speed sensor, and running through the diagnostic procedure in the WSM. At the end, everything checked out and the WSM said "replace the cruise brain". I did the solder trick and it works perfectly. It really takes off when I hold the cruise stalk forward. Basically WOT...

Voytek

It looks like one on the comparators within Control Unit is not working. Typical rebuilds go for $160. I have done mine, 1987 5 sppeds, Cruise Control (still vaccum based) rebiuld by Mark and it works superb one year later. It was around $60. Copntact me if You need to try this source. Mark is extremely busy and He really would prefer not advertise at this time, but he would help people in need. He also is looking for 928!!

Gregg K

I heated up the solder joints on mine, and that's all it took. Works fine now. Here's my suggestion- just heat up half of the pc board joints. Chances are you'll catch the bad joint without having to reheat all of them. And the other suggestion is to start on the side with the ic chips. I believe that's where the problem lies. And from the post by Voytek, that is probably why.

G Man

OK. Now if you would be so kind as to tell me where I can find the board with the joints that may be bad.

SharkSkin

The board is inside a paperback-sized aluminum box that sits on top of the center tunnel way up under the center console, just behind the firewall. Mine was held in by a tiny self-tapping screw on each side, so I had to pull both side covers off the console. The only tool I could get in there was a 5.5mm combo wrench IIRC. I could be wrong about the exact size... I was so annoyed at not having the right tool I picked up this ignition wrench set from Sears and one of those worked.

If that link doesn't work just search the craftsman.com site for item 00947979000.

Anyway, you will have to gently pry the swaged tabs away from the plastic endplate and slide the cover off the PCB. Gregg makes a good point about having a good chance of fixing it if you solder the correct half of the board, I tend to be a lazy bastard about this stuff and I soldered all of the joints including the pins on the end connector so I wouldn't have to keep pulling the damn thing out over and over. YMMV, & HTH

H2

I've had two cruise control boards resoldered and both now work fine. The second one "surged"...the first was intermittent and usually didn't work but was on again/off again. The tough part is removing the plasticized coating on the solder joints w/o hurting the board. I'd just have a local electronics person do it they're usually good at making sure to make tight solders. Takes about an hour and often works. Worth the try. My first one is still working after a year. Even if I had to pay full price for a replacement I'd do it since it saves me from getting expensive speeding tickets. I can't afford another ticket.

Harvey

Garth S

As the cruise control has been the only non-operating system on my '80, (for ~3 years), 'youse guys' motivated me to pull the control box this AM. Dave is correct - everyone else lies!! there are 2 self tappers holding the in, not one! - and they are 7mm.
The passenger side is easy, but the drivers side took me an hour with a 5" long 7mm wrench and a flashlight to get ~1/16 turns while bent like a pretzel: that bolt will never make it back.
If you are lucky, you'll have one of those mythical boxes with one screw!

SharkSkin

Garth, that explains why so many of these only have one screw on them. I put them both back in, either because I am a masochist(explanation obvious) or because I am a sadist(why make it easy on the next guy, if any?).

Naw, seriously... I screwed it back down with both screws because I didn't want a new rattle. Yeah I could have stuffed something soft in there, maybe even double-sided tape but I tend to be fussy about stuff like this....

Garth S

.... well, I tend to also be fussy, but there are limits . I've just gone through my board with a Fluke meter - and cannot find a cold solder joint, nor an intermittant.
Sounds like the shotgun approach is near - reflow all joints in the hope of catching something. What do you think?
G Man, not intending a hijack - this may help you as well

SharkSkin

I didn't put a meter to it, but mine looked perfect. I soldered it anyway and solved the invisible problem.

Marc Schwager

I had this identical problem on my 1980. If you are dealing with the same thing, notice that you can engage the cruise while going slow and it won't floor the car until you hit 30mph. Makes for an exciting ride! This will generally tell you that your cruise computer is at least partially operating and you may have the same problem I had.

Look in the WSM (27-12) for a simple 5 step diagnostic with a voltmeter.

Pin 12 is ground. Turn on the ignition and check the voltage between pins 9 and 12, and then between 10 and 12. It should be zero until you push the lever (forward or down). In my case between 10 and 12 it was 12V. Both can cause a full throttle condition. 9 and 12 are a yellow and blue wire that head up to the switch on the column. When the switch was assembled, they pinched the blue wire. Re-assembling it carefully and a bit of electrical tape fixed the problem. You'll need to pull the wheel to get to the switch, but IMHO it's a lot easier that resoldering the board which I also did while I was hunting down the problem!

HTH