When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 77 'Vette, pretty nice, about 100,000 miles, with a strange speedometer problem. Going down the highway about 60 or so, the speedometer reads about 150, with the needle bouncing all over the place.
The odometer works properly though, and is accurate, but the speedo is WAY off, so it is not, repeat NOT, REPEAT AGAIN NOT, the speedometer gears in the transmission, it is apparently something inside the speedometer itself. None of the mechanics I've talked to have clue one about what the problem is. Wondering if anyone here might have an idea. Thank you.
Not certain about anything, just a guess, but don't know what else the problem could be. And there's NO WAY I'm tearing the entire dash apart to get the speedo out, that's way beyond my meager skills.
Ok. Well, there's really nothing between the speedo head and the transmission, other than the cable, that could cause what you're describing. So, in that case, good luck to you.
The cluster has to come out period!
I to own a 77 and just replaced my lower dash pad (the panel that houses the Speedo/Tach)
It is a time consuming and frustrating job...
This was my first time for me pulling both the column and speedo housing...
I have dropped the column before to service some light bulbs but nothing that deep...
What I have found about the speedometer assembly inside there is an assembly and the parts book calls it Worm & Magnet Assembly 1st...
The same part was used on ALL Corvette Speedometers from 1970-1977.
So if you can find a parts speedometer between those years it will fit in your 77 no problems...
The left page has a part number 25015622 That is a 1977 Speedometer, you will see I underlined the Worm Mag Assembly part number
The right page has a part number 6496850, that is the 70-74 speedometer, notice the underlined part number is the same as a 77...
It's not a hard job, but if you have no patience pay a pro $$$$ to do the job...
One thing you may want to try, is attaching an electric drill to the cable at the transmission end. Run the drill IN REVERSE and have someone look at the speedometer. My two cents, if you, or someone you pay to remove the speedometer, be smart and have the electronic tach repaired at the same time. Removing the speedometer and tach was the worst job I ever did on my 1973. I still have nightmares, the main bundle of wires are routed on top of the speedo/ tach and after 50 years they are as hard as a steel rod. Good Luck
I've had mine out a few times over the years. The last time I replaced every bulb socket and extended all the socket wires by about 6 inches. Makes removal and installation much, much easier.
Remove the dash top pad first. Drop the column down a bit. Really not that hard.
Take the seat out of car when working under dash. Only a few bolts hold seat in and without seat makes life endurable.
This especially true if you're no longer young, tender & lithe.
77 Corvette Speedo problem
