1960s 68 DeVille - speedometer stopped working

[chrisbutnut]

My speedometer stopped working tonight.  It has worked fine previously.  Any suggestions on what to check first before I start taking things apart?  I've read the sections on the speedometer in the 68 shop manual, and about the wave washer holding the cable to the instrument cluster.  I do not want to remove the cluster itself.

I should mention that I pushed the trip odometer knob in to try to reset the trip odometer.  That didn't do anything, so I turned it, and that moved the digits on the trip odometer almost back to zero, but not quite.  Could that have caused the speedometer to stop working?

The only other thing I've done recently is install a new map light, as mine was missing.  In order to get the light to work, I had to run a ground wire to a screw on the bottom of the steering column, inside of the lower dash access panel (under the steering wheel). 

Thanks.

[The Tassie Devil(le)]

The first check to make is to see if the transmission output of the Speedo Cable is good before anything.

You need to lift the car to access the end of the Cable, and attach a battery drill to the inner cable, and rotate it with someone looking at the Speedo Needle to see if it is moving.

The Odometer has no connection to the Speedo Needle, as that is magnetically controlled by the spinning cable.

The above is just a start.

Bruce.

[TJ Hopland]

Ya checking the cable at the transmission end would be my first stop.  You can usually just give the cable a spin with your fingers and make the needle bounce and that will also give you an idea if there is stiff spots in the cable. 

[chrisbutnut]

I remembered one more thing that I did, which is probably the culprit.  The inside of the gauge cluster (behind the clear plastic cover) had a bunch of fine dust inside of it, most likely from when the body was sanded prior to painting.  I used a can of compressed air to try to blow it out, first by sticking the long thin plastic straw that comes with the cans through the holes where the clock adjustment and trip odometer adjustment are.  That didn't really do much, so I switched to the air gun on my air compressor, and stuck the rubber tip up to those holes.  It made it a lot better as far as the dust goes, however now I am worried that I blew something loose, preventing the speedometer from working.

The car is going in soon so my mechanic can replace the transmission mount, so I'll have him check the speedometer cable at the transmission end, however my fear is that I'm going to have to remove the instrument cluster and open it up.  Luckily I have an identical donor panel in case I need any small parts or pieces. 

Thanks for the responses!

[bcroe]

You might have a broken cruise control module, the
speedo cabling runs thru it.  Bruce Roe

[chrisbutnut]

My car doesn't have cruise control, but thank you.

[Big Fins]

If the cable is good, meaning from the bottom it moves the needle in a steady fashion, the next cheapest thing to look into is the gear in the side of the transmission case. The square drive of the cable may be rounded out or the teeth chewed off of it.

There are a few differing gear colors depending on which rear gear you have. Match the same color if that is the issue.

I hate tearing a dash apart. I think '69 and '70 were the easiest. My '76 is a nightmare.

[chrisbutnut]

If the cable is good, meaning from the bottom it moves the needle in a steady fashion, the next cheapest thing to look into is the gear in the side of the transmission case. The square drive of the cable may be rounded out or the teeth chewed off of it.

There are a few differing gear colors depending on which rear gear you have. Match the same color if that is the issue.

I hate tearing a dash apart. I think '69 and '70 were the easiest. My '76 is a nightmare.

Thank you.

[The Tassie Devil(le)]

I remembered one more thing that I did, which is probably the culprit.  The inside of the gauge cluster (behind the clear plastic cover) had a bunch of fine dust inside of it, most likely from when the body was sanded prior to painting.  I used a can of compressed air to try to blow it out, first by sticking the long thin plastic straw that comes with the cans through the holes where the clock adjustment and trip odometer adjustment are.  That didn't really do much, so I switched to the air gun on my air compressor, and stuck the rubber tip up to those holes.  It made it a lot better as far as the dust goes, however now I am worried that I blew something loose, preventing the speedometer from working. 

I think you might just have hit the nail on the head.  The guts of the Speedo does not like that sort of treatment.

The hair spring could have been compromised, plus with all that dust moving around inside, where it is supposed to be squeaky clean is not good.

Lastly, does the Odometer rotate as you drive?   If it does, then there is nothing wrong with the Speedo Cable.

Bruce.

[chrisbutnut]

Took it for a drive, and the odometer is working, so that eliminates the speedometer cable.  I guess I'm taking the instrument cluster out, which worries me with the brittle plastic and all.  Is there someone who repairs these would I could send it to, and could hopefully turn it around quickly?  Otherwise, I'm left to either try to figure out the issue and fix it myself, or try to swap parts from my donor dash.  I've started taking that one apart so I can see how it works.