View Full Version : Speedometer rehabililtation

12-14-2006, 08:24 PM
I'm getting ready to start assembling my M5 dashboard and will start by resurecting my instruments. Is there an insturment repair guide that I could use to get started cleaning the speedo and testing the the oil pressure, fuel and temp gauges? Thanks. David Orth 48M5

John Kirchhoff
12-14-2006, 09:33 PM
I've repaired several mechanical tachs and speedos. If the needle bounced around when in use, there's a brass bushing the needle shaft rides in. Often times the grease is old and stiff, using some cleaner and then oiling the bushing will make them work like new. Other times the bushing is quite worn and thick grease will help to settle the needle down, but not always. Don't pull the little thorn like wedge that holds the coil spring. If you do, you're going to have a really fun time recalibrating it again. I've corrected factory miscalibrations and there's a lot of trial and error to it. The hardest part may be getting things apart, don't know how yours are made. If you spray any kind of cleaner or lubricant, make sure you don't get any on the face of the dash or glass. I could tell you how to roll back the odometer, but I wouldn't want you cheating yourself!

There's really no lubricating ammeters, temp or fuel gauges. There's just a little spring in most of them.

Oh, if your speedo needle ever takes off like a airplane propeller, the little spring has broken or come loose and you'll be doing more serious repairs.

12-14-2006, 10:51 PM
Thanks John. Your info helps. Is there a way to safely bench test the speedo by turning the mechanism with a slow speed drill motor or some other device? I've not had this speedo in a running vehicle. I'd like to test after I clean and lube and before I install.

John Kirchhoff
12-15-2006, 08:32 AM
One way to do it would be to take a nail (maybe 16p sinker or box), cut the head off and file the other end down square about the size of a larger wooden matchstick. Slip one end into the drill and the other into the square hole in the back of the speedometer. You'll probably need a reversable drill because you'll have to run it counter clockwise. A wooden matchstick itself might work as long as you don't bust if off in the speedo. Actually I'd prefer the matchstick since the metal part on the speedo you're sticking it onto is most likely brass and a nail is harder than brass. Too much wallowing around and you could ream out the hole. A piece of old broken speedometer cable would be perfect if there's any laying around but most of us don't keep busted ones (except maybe me, don't ask me why). Sometimes there can be hardened grease around the brass tip the cable goes into that can cause the needle to jump around as the cable winds up and cuts loose repeatedly. If any of the internals of the speedo are shot, there's a good chance you can find replacement parts in one off of a different make of car. Stude Hawks are Stewart Warner (don't know about the older ones), lots of farm tractors use SW and I think (don't hold me to this) I repaired a SW tach once with parts from a 60's GM vehicle. I think the Chrysler speedo of the same vintage was different, probably a different supplier.

If you need to get into the speedo, their internals are really quite simple. The cable turns a magnet that rotates on its own shaft while the indicator needle is mounted on its own shaft attached to a cup that fits around but doesn't touch the magnet. As the magnet turns, its magnetic field drags the cup along with it which is held back by the little coil spring that looks like a watch spring. So if the needle dances back and forth, first try cleaning and lubing the cable shaft as it's usually the culprit.

12-16-2006, 02:57 AM
If those little bushings are well and truly past their use-by-date, take the speedo to an old-fashioned clock maker. He will have the smallest lathe you have ever seen, and will have no trouble making new parts.
I've had a couple of old speedo's repaired this way, with total success each time (and at very reasonable prices).

Robert Crandall
01-17-2017, 09:38 AM
I found this information in a search. The speedometer in my 1949 2R5 appeared to be internally damaged when I bought the truck in 1980. I found a gage cluster which included a working speedometer a little over 20 years ago. I am now ready to get around to installing this speedometer into my truck. I separated it from the cluster, and the internal parts seem to be fine. The lubricant has dried which makes the drive too hard to turn.

Lubricating this mechanism is suggested above. My question is: What and how much lubrication should be used?


Robert Crandall
01-17-2017, 01:24 PM
A follow on to my question in post #6 above: Does anyone know of a source for the plastic tubes that surround the light bulbs and the red disc that covers the bright lights indicator?


01-17-2017, 03:27 PM
Jalopy Journal had a photo of a kit that had replacement parts for speedos, had the brass bushing and other parts, skimmed it a few years ago but decided on another way. Might Google Stewart Warner and see what comes up.

01-18-2017, 04:31 PM
Robert Crandall: I think Studebaker International (and perhaps other Stude vendors) has NOS speedometers for the early 2R5 trucks.

For the red plastic, most auto parts stores have red plastic film for temporary repairs on taillights. Try a piece of that. Pull off the cap and place a disk of red plastic in the cap. For those tubes, I think they were made with blue-tinted plastic film that may have included some glow-in-the-dark properties. The inside of the housing for the speedometer may have been painted with blue-green glowing paint, as well. I can't imagine that a 6-volt bulb gave off enough UV to do much activation of the old glowing phosphor materials, similar to what was used on the inside of old TV screens. I replaced my plastic tubes with some pieces of diffuse Mylar drafting film and left the old paint in the speedometer housing. But, Google for glow-in-the-dark paint and you'll find it at craft shops and Amazon.

01-18-2017, 05:04 PM
My new speedo from speed shop says, if cable is turning 1000 rpm speedo should read 60 mph. I installed it in my 49 so I could drive it until I ( or next guy ) could get original fixed, hate to wait a year for a shop to overhaul old one, it was sticking on large numbers, and that ain't the cable.

Robert Crandall
01-19-2017, 09:45 AM
Thanks for the additional information. I have had no luck finding speedometer repair kits, but many repair services. I see the speedometer in the SI catalog, but I am not ready to buy that. I just placed a $100 plus order with SI for other parts. I am limited at how much funding I can put into my toys. My date code 1977 tires should be higher on the priority list also.

If I can get my spare one turning freely, then I will be happy with it. I will check the red film. What would be the implication of not using any tubes around the white bulbs? I do plan to use the face and the interior paint on the gage as is. It will match the other gages.

Robert Crandall
01-20-2017, 07:38 AM
An update. A few drops of AT fluid with acetone freed the shaft up nicely, and the unit seems to work fine. I will follow with the red film recommendation and find something to use for the bulb shields.