Speedo Needle Jumping and Odometer Not Keeping Mileage

[Eddie 70]

This is something sort of new to my car. I have a fairly new rebuilt speedo and it has been keeping up with mileage for the last 6k miles. For some reason now the needle is jumping. There is an audible click and then the needle jumps so there is no real way to monitor my speed. I have the speedo out on the bench and was wondering if anyone has any good ideas on what to try what might be the problem. I have been using the short cable that goes to the odometer reset to drive the speedo and twisting it by hand on the bench. It will still make the click sound.

Any help is appreciated. s:

 

[petes74ttop]

Sound like the odometer drive gear is worn http://www.corvetteamerica.com/ part # 1604 PG.

 

[Eddie 70]

Pete thanks for the reply. I can see this gear and it is not turning that I can tell when I drive the speedo head. Do you know where the wear occurs on this gear? I will check it closer later this evening and see what I can find out.

 

[petes74ttop]

The gear is at the right side in the picture, I have a "How To" remove and replace that part. PM me your email address and I'll send it later tonight or tomorrow AM, Pete.

 

[Eddie 70]

Here is where I am starting from. Notice it stopped at 31000 miles on the dot. :thud:

Here is the speedo with the face and needle removed. Just pull on the needle.

The bar across the front removed.

 

[Eddie 70]

Okay, for those who may be following along.

Here is the speedo driven gear out of the speedo. It looks okay. It does have some small wear to it.

Here is the naked speedo head unit. I am not sure I should dig further into it yet. Everything inside seems to be working smoothly now and no clicking.

Here is the trip odometer and its retaining clip removed from the head. This works smoothly and I suspect no problems from it. You can turn the shaft and the the miles will accumulate correctly.

Here is the odometer part of the speedo and its retainer. Now the shaft that goes through the center is free to rotate in both directions. I believe this to be correct. The driven gear on the end is what drives these numbers and it appears to be okay. Some small slight wear on it.

Another pics of the odometer with its "legs" taped to keep the together. I assume this is to make installation of the odometer easier. It appears that my tenths digit is frozen in place. Does anyone know of a way to free the tenths digit? I will keep plugging at it and fix it correctly or fix it till its broken. :laughing:

 

[Eddie 70]

Any good tips on how to get them out? It does not look like you can just pull on the ears.

I have been playing with the odometer. The only way you can add mileage with my odometer is if you let the e-clip between the tenths and miles turn loose. Then the odometer works correctly adding mileage. This makes me think the tenths place has a problem. Am I going down the correct path.

 

[Eddie 70]

Okay, I don't know what I just did, but I put my screwdriver between the ends of the clip on the tenths position, I got a small pop sound. So I decided to see if that helped. Voila', my odometer is working correctly now. I have no idea what I did but it will now work like it should. Do you think I should keep trying to take it apart since it is now working?

 

[Eddie 70]

thanks for the help on this one. I don't know what I did to free up the odometer but it worked. I could not stand it so I put the head all back together and tried it out with the drill motor. I ran it for 1.2 miles. So far so good. Only one problem, I forgot to put the ears back into position on the trip odometer and wound up with 111.4 miles. Go figure. Easy fix there. More pics

Here is the head all put back together and 00000 miles on it.

After running the head unit with my drill motor for 1.2 miles.

And here are the ears I mentioned earlier. Gotta get these dudes in place or you get crazy readings.

And here is the whole speedo put back together and ready to run again.

 

[Eddie 70]

Pete, thanks for the email. I have been looking online for the white and black gears and will replace both of them this week. I see a small amount of wear on the white gear. The black gear looks to be fine from what I can tell. But both will be replaced and hopefully this will be behind me again for another 6k miles. LOL!!

 

[73shark]

Great work! Don't you just love it when you get something to work but know not what you did to fix it?

 

[Eddie 70]

It may only work for another 6k miles but that could very well be another 5 years. By then, I will be ready to tear it apart again.

 

[Bwmurph]

I've been following this thread with interest. My '71's speedo works fine, but the odo and trip odo do not work at all. I'm not sure if I have the patience or skills to take apart the unit like you did, but I would like to get it out of the car to possibly send off and get it repaired.

So that's my question: Just how hard is it to get the unit out of the car ? I've heard it is a real PITA, but I'm willing to try if it's something that I don't have to take the whole dash apart to do.

Any help would be appreciated,

Bernie O

 

[Eddie 70]

Hey Bernie its not too bad of a job to get the dash pad out. You will have to drop the two bolts out of the support for the steering column in order to gain enough room to remove the dash pad. There are 3 screws across the top of the dash pad, two on the left side and two going through the gauges into the pad. After that, unplug all the lights, make a little map so you can reconnect the vacuum lines correctly at the headlight switch and vacuum relay on the lower part of the dash. Unplug all of the bulbs. Unplug the speedo cable and tach cables. After that I think it should just come right out. Hopefully I did not miss anything but I believe you can do it. As far as I am concerned the hardest part is disconnecting the speedo and tach cables.

 

[minifridge1138]

Did this also fix your jumpy needle?

 

[Bwmurph]

Eddie,

Thanks for the input. I doubt I'll get to it anytime soon as I have too many other projects for both the cars as well as the house and inevitable "honey do's". I'm hoping sometime this summer and you can be sure that I'll be posting on the CAC when I get myslef in too deep.

Thanks again,

Bernie O.