Question: '81 Cruise Control/Speedo Question

[Mark Rittinger]

I have an '81, 350, automatic. It has Cruise Control...though it has never worked properly since I've had the car...it accelerates when turned on.
When I got the car, the speedo didn't work, so I replaced the lower speedo cable about 8 years ago. That worked.
This summer , the speedo needle began to bounce. Since the lower cable was replaced, I figured it had to be the upper. That was a fun project...but, I got it out, cleaned it, greased it (not to within 1/3 of the speedo) and replaced it. The needle still bounced, but not as bad and mostly at slow speeds.
Today the needle stopped completely.
Is it at all possible the that cruise control transducer refuses to spin the upper speedo cable if the lower cable is still functioning? I only have insurance for the next week, so this will be a winter /spring project to get the CC and the Speedo both working properly.

Thanks in advance for any help.
Mark

 

[Antz81]

Easy to test where the problem is by using a drill to spin the cables and seeing if you speedo works. Spin the upper cable, if you speedo doesn't work replace the upper cable, if not move on to the lower cable. if it doesn't work it could be the cruise control like you say or a bad cable again (not very likely). If it does work you have a problem with one (or both) of the gears.

 

[toobroketoretire]

Bouncing Speedometer Needle

The only thing that can cause a speedometer needle to bounce is a cable that is either a bit too dry or has a bend that is a bit too sharp. The cable is actually a tightly wound .104" diameter spring and when the cable has trouble turning it'll "wind up" then "let go".............causing the needle to bounce. The easiest cure of a bouncing needle is to buy a longer cable that can be routed with BIG bends. Never use any lithium grease to lube the cable as the grease will eventually dry out then turn to a really stiff gum. I have found ordinary Vaseline will work great but I usually use powdered graphite mixed with ATF so it'll adhere to the cable.

 

[Vettehead Mikey]

Today the needle stopped completely.

See if the odometer is still registering. If yes, the speedo head needs to be repaired.

Is it at all possible the that cruise control transducer refuses to spin the upper speedo cable if the lower cable is still functioning?

Yes, but this condition is rare. Usually the transducer fails internally. Follow Antz's advice.

 

[Mark Rittinger]

Thanks. Shes bottled up for the Michigan winter, but I will have a good look in the Spring. The Odo wasnt moving either. I used a teflon type grease on the short cable when I took it out for a look...Lower cable was replaced, but I suppose it COULD have taken a crap already. I will know more in April Thanks guys!

Mark

 

[Mark Rittinger]

OK, I got it up on stands for the Spring once-over.
The lower cable that was replaced once already was broken off in the transducer. Ordered a new one, and that one has a metal end on both ends.
Removed transducer and ordered a reman unit. Got that today and its a perfect match.

This weekend I'll work on putting her back together.

The big question...the new lower cable seems dry out of the box. What should I lube it with?

 

[bill81vette]

graphite! if you can find it,or nothing they used to come with some type of lubricant on it.
I don't recall using anything on mine when I put mine back together,
a previous owner had a 1 piece in its place.never have had an issue since....

 

[Mark Rittinger]

Ok, thx. All the parts have arrived, time to get scraped up n dirty lol

 

[Mark Rittinger]

OK, here's where I'm at.
I replaced the lower cable, and I replaced the CC transducer.
I cleaned all contacts, and checked all the vac hoses under the hood. Everything looks good...hoses seem flexible yet, connections tight.
I took it for a drive.
I turned it "on", and hit the Set button. Nothing. I fiddled a little with the Set button ( it probably hasn't been used in 25 years), and it did "take", but let go after a few seconds.
I tried "Resume", and it would do the same....take for a few seconds, then let go.
Out of curiousity, I held the Resume to the right, and the speed held steady.
Got home, took the little cover off the CC switches, hit them with electronic cleaner, and put it back together.
Still doing the same thing...grab a sec, then "let go".

I have the sheet that came with the CC transducer, and it has a list of electrical connections to verify.
Seems like maybe its one of the switches having to do with the brake pedal, or something under the dash...it WILL grab and hold speed ( longest was for 7 seconds) but something is making it "let go".

Ideas?

 

[Tom Bryant]

Your cruise control release and the brake light switch is a combination switch. It is the cream colored plastic switch on the brake pedal arm. Verify visually that the switch plunger is retracting all the way inside the switch when you release the brake pedal. There is about 3/8 to 1/2 inch of threaded cream plastic showing between the flat on the brake pedal and the switch mount/adjusting sleeve on mine. The plunger goes all the way inside the switch with the brake pedal released and all you see is the threaded plastic with maybe just a slight bit of the plunger showing. The circuit should then be on and the cruise should stay engaged.

Next check the brake release switch itself. The orange and white wires that plug into the bottom are for the brake lights. What you are going to check are the terminals for the green and tan wires on the rear plug. You should have power at both terminals (tan is circuit 900 and dk green is circuit 83) with the ignition switch On in the run position and the lever switch (On-Off-Resume)in the On position; brake pedal released.

There should be no power to the tan wire once the brake pedal is depressed.

When you depress the brake pedal the switch opens and electrically releases the resume solenoid valve to cut off vacuum to the transducer. The transducer is then disengaged and the cruise releases until you hit the resume or on again.

If you need to adjust the release switch it is a simple procedure. Let me know.

Tom