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As I was driving the Vette to the inspection station, I noticed a speedometer problem. The speedometer bounces between 0 - 20mph at any speed - occasionally it may reach 30mph. Any helpful pointers will be much appreciated - I will start with the cable in the tranny, see if it is intact, spin it with a drill and see what registers in the cluster and inspect the plastic drive gear. It does not have cruise control.
I had this exact same problem last year with my 79. The only difference is I have cruise control. I pulled the lower cable and cleaned it really well as the original lube had become very hard and used a graphite dry lube and now the speedo works as it should. Good luck
I pulled the cable from the tranny. It felt a bit loose as if it was not threaded completely. Nevertheless, I took it out and removed the sleeve assembly and the plastic driven gear. The gear seems to have wear. It is blue and has 20 teeth. The sleeve assembly has some buggered threads from the last time bubba was playing with it.... I hooked my drill to the speedo cable and the speedo works just fine. At full speed, reverse, it registered about 50MPH.
What is a good source for the sleeve assembly and driven gears? Zip did not have them and Eckler's seem to have a 19 tooth one..... appreciate the help!
I don't think that gear is your issue... In most cases the driven gear is not the issue even though it shows wear. While your old gear shows some wear, it's still meshed in the drive gear in the tranny.... If the driven gear was the issue you'd see teeth missing off the gear completely in most cases.
A bouncing needle is usually caused by a cable issue or a head issue in the speedometer.
So before I purchased any gears, I'd probably remove the cable and lubricate it first...
While the above bulletin from GM/Delco say's only use their lubricant, you can use any graphite style lubricant available from your local parts store.... just use it in the described method above. If you can't find it, I've got plenty of it in stock as well.
If the problem persist then I'd take a look at the speedo head. The head on the 1978-1982 speedometers is pretty resilient though with the only issue being the first worm bushing which is plastic and can be replaced pretty easily by a good shop. If you then need the gear, I've got them.. https://willcoxcorvette.com/corvette...oth-blue-56-81
Willcox
Last edited by Willcox Corvette; Oct 31, 2017 at 10:11 PM.
A bouncing needle is usually caused by a cable issue or a head issue in the speedometer.
So before I purchased any gears, I'd probably remove the cable and lubricate it first...
While the above bulletin from GM/Delco say's only use their lubricant, you can use any graphite style lubricant available from your local parts store.... just use it in the described method above. If you can't find it, I've got plenty of it in stock as well.
Awesome, thanks Wilcox! Do I remove the cable completely with the sheathing (which would be tons of work) or can I just pull the internal metal part of the cable from its sheathing, lubricate it and shove it back in?
To close this thread out - I removed the cable from its sheathing from the cluster side, cleaned it thoroughly with denature alcohol using a rag and then lubed it with dry lube. I also replaced the transmission driven gear and sleeve assembly with new units. The speedometer now works beautifully.
To close this thread out - I removed the cable from its sheathing from the cluster side, cleaned it thoroughly with denature alcohol using a rag and then lubed it with dry lube. I also replaced the transmission driven gear and sleeve assembly with new units. The speedometer now works beautifully.
79 L82 Speedometer issue
