Have a '77 and the odometer just quick working, speedometer works and is accurate. I've had cables break, bind and gears where out but never had just the odometer quit and the speedo continue working. Thought I might save some time by asking for some help on where to look for the problem.

 

Hope you get an answer because my 77 was that way when I bought in Jan of this year. Speedo works but odometer

 

Years ago, I had a 68 vette with a bad odometer. The speedo worked fine. I pulled the speedo and brought it to a speedometer shop (they exist!) and they fixed it for about 60 bucks (1988 dollars, so I can't say what inflation will do to that number).

Temvette72

 

More than likely the plastic worm gear has stripped. Here a picture of what the mechanism looks like. You can see the white worm gear towards the back that drives the main odometer (black gear) which in turn drives the trip meter.

 

The worm gear may or may not be stripped, here is what I had:
I recently rebuilt the speedo on my 76, I had the same problem. In my case the speedo worked and the trip odometer worked, but the odometer (total mileage) did not work. I found out that the outer ring (in the photo, the black ring on the right side of the #8 at the top of the photo) on the odometer wheel drives the wheel next to it and in turn it drives the next etc. The outer ring apparently had a pin or protrusion that contacted the next wheel and that pin was gone, so I drilled a very small hole thru the outer ring and pushed a brass pin thru it to contact the next wheel so that as the ring makes one revolution, it moves the next wheel to the next mile number and so on.

You can buy a new odometer wheel from Dr. Rebuild or maybe someone else, the cost is about $40.00 and then you do the work. The worst part of the whole job is pulling the dash and removing the speedo.

 

Great photos and good info. I'll pull the dash and see what's going on.

 

If the speedo has a plastic worn gear in it, then it’s had a head replaced in it before.

We have in our repair help section on our web site an exact description of what happened and what is causing it!

Here is the link: http://willcoxcorvette.com/product_i...ducts_id=24526

Here is the text:

Why Did My Odometer Stop Working

All Corvettes from 1953-1977 used basically the same design for the Speedometer and it was called a “W” Series Speedometer.

In most cases when the Speedometer is working and the odometer is not working you are in need of repair. The answer to the problem is normally not the odometer but actually in the speedometer head. The brass oil impregnated bushing in the back of the head will wear out over the years!

This bushing runs most of the entire length of the first worm and magnet inside the main frame and will allow the magnet and first worm to ride in and out as well as from side to side if bad. Early evidence of this issue is a slight ting or a scratching noise coming from the speedometer.

If you take the speedo out of the car you can remove the needle by turning it counter clockwise and pulling outward. After removing the needle, take the two screws out of the face and remove it. You will see a "Jewel Plate" that is held in place with two tiny screws. Remove the jewel plate, and remove the speed cup retainer “FIELD PLATE” by taking out the two larger screws that hold it in place. When you remove the speed cup retainer “FIELD PLATE” you do so by pulling up on the needle shaft. It’s very important to keep these two parts together and to lift off the speed cup retainer “FIELD PLATE” by the needle shaft only! There is a tiny spring that is attached to the speed cup and hooks on the “FIELD PLATE” adjustment arm and if you break, stretch this spring you are just creating another problem. Do not move the adjustment arm; this is the arm that calibrates the speedometer so moving it will mess with the needle reading on the face.

Once you get the “Field Plate” and the speed cup out of the way, you will see series of gears below it. The cross gear (second worm) will be worn out! This is the gear that drive's the odometer and if it’s bad then you need a repair that you can not do at home. There is a bushing in the side of the housing that holds this gear in place and it can be driven out with a drift. Once this gear is out, inspect it and if this gear is worn out you can replace it if you can find one available. But replacing it will only be patch. Since the first worn rides on the second worm, when one is bad then it’s almost a given the first worm is bad. Spending money to replace the gear will only be a waste since the matching gear will eat it right up once installed.

The second worm gear will be metal if original and plastic if a replacement. The chance's are it is a metal gear unless someone has already been inside and replaced it. When the brass bushing wears out in the back of the head it misaligns this gear to the second worm and wears them both out. You can replace the second worm gear and it might last a little while, but it will probably just eat it right up again. (Like a tach drive gear inside a distributor). When you bought the 6456122 frame from GM it came with the frame, the first magnet (flat magnet) and worm and the second worm installed.

In simple terms, if the odometer is not working then you should consider removing the speedometer and sending it in for repair. Basic repair to a speedometer is about 95.00 and it includes a complete rebuild. This is a rebuild and not a restoration. We do not recommend you send in a speedometer for restoration without sending the tach with it. If you restore the face on a speedometer, then it will not match the face on the tachometer.

Hint: Never use an oil lubricant on a speedo or tach cable. The cable is reverse wound and it will pull the oil in to the first worm and magnet bushing. This bushing is already oil impregnated and adding grease or oil to it will only cause early failure. There is a special lube you can purchase for the cable and you simply pull the cable from the housing, lube it and then wipe it off. Enough will stay on the cable to allow for proper lubrication.

Property of Willcox Inc. 2007 all rights reserved.


Here is the picture: