Speaking of Gauges...

[Jim Shepard]

I posted this question once before and got no response. With all the interest Merle's question garnered, I thought I'd try again. My speedo doesn't work. I've disconnected it at the back and, with the truck moving, confirmed that the cable is good. When hooked up, the odometer works, but no speedo. The needle does jump around a little, though. I, too, have debated taking the speedo apart because of the grommets holding the housing together. As it now sounds like that may not be the issue I thought it was, my only question now is: what am I looking for once I get inside?

[Norm's Coupe]

Jim,

Sounds like you may not need to take your speedo apart to get it going correctly.

When I bought my 48 Plymouth Coupe the speedo cable was broken. Replaced it and the speedo still did not work. Took it out of the car, then put a couple drops of penetrating oil into the hole in the back where the cable goes. Let that set overnight. Next day I used a screwdriver bit to move the speedo gears. Got it moving freely, then put it back in the car. It's been working great ever since. You can also use 3 in 1 oil or some other light weight oil. Don't use so much it goes into the face of the odometer though.

[grey beard]

Jim,

These things are pretty simple. What you have inside is the needle held in place almost like a balance wheel in a watch - a very fine fulcrum and bearing surfaces. The needle assembly is spring loaded with a fine hair-type coil spring that keeps it at zero. The needle is connected to a drum in the back that sits inside a pair of revolving magnets. That's about it, except for the mecanically driven odometer, which is all gear drive.

If you can lube the bushing inside the head, where the cable enters the housing, either by letting penetrant soak in or by other means, you may be able to fix it without having to split the case open. That's the place to start.When I work on these, I use a fine Phillips bit in my cordless drill to spin the thing, to see if the hand moves at all. Sometimes the hand comes loose from the shaft. In a few instances I have had to bend the revolving magnets closer to the drum that turns the needle. AND if it looks gummed uip inside from being lubed with engine oil, try a little brake clean - whaever frees up the needle JMHO

By the bye, when a real speedo shop calibrates a spedometer, the only adjustment (other than the gear drive for the cable( is the air gap between the magnets and the drum.

Good luck with fixing it. Let us know how things work out.

[Jim Shepard]

Thanks guys. I'll try it and let you know.

[MBF]

Once you have it cleaned up and working I believe that there is a small screw about 1/2" long near the cable input. If you take out that shafted screw there is a wick behind it. You may want to put some lightweight machine oil on the wick while you have the unit out. Mike

[Guest wrightkoss]

Does anyone have any idea about the speedometer that is attached to the vacuum for the 2 speed rear end? Can you just take that off and do the same work on the needle or are these a bit more difficult. Also to clean up the vacuum and assure that it is working correctly, how big of a job am I looking at?

[anthonyb]

The speedometer is the same but there is an additional adapter unit attached to change the gear ratios in the speedo head. It's a fairly straightforward process to disassemble and clean. The major problem you may have is if the diaphragm is shot. They're hard to come by.