'66 Speedometer Repair

[Ralph Messina CLC 4937]

I have speedometer that is not working on a ’66 Cadillac. I’ve tested it and believe the magnetic pickup is bad. Is the magnetic pick up serviceable?  I’d like remove and replace just the speed pickup, not the whole face and odometer.

Thanks,
Ralph

[m-mman]

How did you test it?
A cable runs from the trans to the back and fits into a square hole. As it spins the magnetic makes a stronger field that moves the needle. Personally I have never see a speedometer that had an 'inoperative' magnet.  There just isn't anything to wear out. . . .

A speedometer shop does (did?) have tools that could increase/decrease the amount of magnetism as a way of calibrating a speedo head. There are specifications that show how many RPMs of cable rotation it takes to show 60 MPH. A shop adds or removes magnetism to adjust the needle.

As for your question, yes old speedos can be dismantled. There are lots of screws but there are some crimps and rivets too. The inner parts of the spinning magnet and the needle assembly generally do not come apart easily but the dial faces and the odometer drum (with the numbers) can be removed and swapped around to make a good one for your car.

Have you checked your cable? That is the most likely cause of speedo failure.

[Ralph Messina CLC 4937]

Thanks for the response. This car has cruise control so I put a variable speed drill on the cable that runs from the cruise unit to the speedometer. I’ve checked the cable at both ends and there’s no damage evident. With the drill running at max RPM the best I can get is 40MPH indicated. That’s also the highest it registers on the highway when I’m certain I’m going much faster. When I first got the car the indicator needle would oscillate between 40 and 70 MPH at highway speed. I had the car apart for three years and should have sent the unit to a repair shop, but was focused on other more pressing issues. I would like to repair it myself in a day or two rather that send the cluster out  for repair now that the driving season finally arrived

[Glen]

Is the error on the speedometer proportional or is it pretty close up to 40 MPH then stop?  If it is proportional then it sounds like the adjustment is off.  If it is close to right until it reaches 40, then it sounds like there is dirt or something preventing the needle from moving pass that point. 

It is easy to check your speedometer, put a GPS on the dash and compare the speed on the GPS with the speedo. 

My Eldorado is right on, my Colorado reads one MPH high. 

[m-mman]

Decades ago I tried to change odometers using a 3/8 drill.  I never got one to go over about 40 MPH. It took hours to add/subtract mileage. I gave up and learned how to dismantle and change the number drum.

As noted if the needle/spring is dry or obstructed it will keep it from showing a fast speed.
I dont have to tell you that ideally the best way to fix it is to do it right. . . . . 

Checking a speedo with a GPS? Hummm . . . why didnt I think of that?   

Where are you located? I think I have a 65/6 speedo unit still stuck in the rafters that I swapped out years ago for the chrome.

[Ralph Messina CLC 4937]

I'm in NJ. When I find another good speedometer I'm going to transfer my odometer and be done with it. It easier than repairing my speedometer. I need another unit before I remove the cluster laying the car up

[The Tassie Devil(le)]

As a point of interest, if you get one that hasn't been used for a long time, take the time to lubricate the internals, especially the odometer gears and shafts.

I fitted a replacement speedo into my '60 CDV, and everything wend beautifully till 25 miles, and then the needle started to go completely out of whack.   Flopping from slow to fast and hitting the stops.

When I stripped it down, I found that the lubricant on the Odometer actuation shafts had become so had and sticky that it was seizing the worm, and ended up stripping the nylon gearing.

I ended up using parts out of the two speedos I had, the original and the replacement, and got it working again.

At this time, I found that the inner guts of both speedos, even though they were 1960, the cross-shafts were different.   One set was Diecast or Aluminium, and the other set was Nylon or Plastic.

The original reason for getting the replacement speedo was that the spinning disk had cone lose from the needle shaft, and even though trying to solder it back on, it wasn't successful.

I have lots of pictures of the operation if you are interested.

Bruce.

[Ralph Messina CLC 4937]

Guys,

Thanks for the help. I just bought that appears to be in great condition.
Bruce, I appreciate the offer of the pics. When I get the unit and start working on it, I my ask for the pics if the job is above my pay grade.

Ralph

[The Tassie Devil(le)]

Most jobs are above my Pay Grade, even when I was working.   Pensioners don't get that much, so I have to do everything.

Bruce.

[Scot Minesinger]

I had 10 great speedometers for this car and I sold them to USA parts 304-724-6600, call them they have many nice ones now.