Oscillating Speedometer

[pbr332]

The speedometer on my '43 GPW recently began oscillating wildly at any speed over 5 mph. I removed the cable from the back and spent about 15 minutes putting engine oil into the top of the cable housing, a few drops at a time. That reduced the problem, but only partially. Does this speedometer need a rebuild?

[Wolfman]

Take the cable loose from the speedo and pull it out where you can see the end and go for a drive.
The cable should start turning in the housing as the jeep moves and speed up as the jeep speeds up.
It should turn smoothly.
If at the speed where the speedo started to jump, the cable starts to stop and jump, instead of keep turning smoothly, you have it. Cable hanging up.
If you have another speedo to attach to the cable, try it and see what happens.
If both speedos do the same thing, cable or drive.
If only one speedo jumps, it is the speedometer.
You can also put a square cable end in a variable speed drill. Spin the speedo up with the drill and see how it acts.

[Wolfman]

Take the cable loose from the speedo and pull it out where you can see the end and go for a drive.
The cable should start turning in the housing as the jeep moves and speed up as the jeep speeds up.
It should turn smoothly.
If at the speed where the speedo started to jump, the cable starts to stop and jump, instead of keep turning smoothly, you have it. Cable hanging up.
If you have another speedo to attach to the cable, try it and see what happens.
If both speedos do the same thing, cable or drive.
If only one speedo jumps, it is the speedometer.
You can also put a square cable end in a variable speed drill. Spin the speedo up with the drill and see how it acts.

[Joe Gopan]

Speedometer cable lube is a grease, post war it was GAA, commercially it was available at auto parts stotes in tubes as a graphite grease mix. If the square hole at the cable end of the speedometer is worn, the cable will slop giving symptoms such as ypurs, dry cable can do it also. Oil can make a mess by seeping thru the conduit. One of the manuals explains only lube the lower 2/3 of the cable as the lube will work its way up.

[artificer]

All good suggestions [Mike's in particular] but it is always best to diagnose rather than jump into anything & we all know about assuming.

This type problem is usually associated with 2 things:
1. the speedo cable....which comprise 2 parts inner cable & outer cable.
2. the speedo head.

Things to check/eliminate that can cause a needle jumping issue....
i. the outer cable can be kinked, rusty internally, mis-routed or not secured properly.
ii. the inner can be dry, rusty, frayed [worn or broken wire strands caused by kinked outer], not long enough. Look especially for shiny spots, indicating an outer cable problem.
iii. the speedo head accumulates dust & the grease hardens plus the sintered bronze bushes can dry out.

[Chuck Lutz]

I'm with artificer here...

Improperly routed cable will get hot and dry out any lube in there then it hangs up.
Motor oil is NOT the best choice....you can get a real tiny tube of SPEEDOMETER CABLE GREASE at the parts stores which is designed for, well, speedometer cables.
NEVER hook up an electric drill to a speedo cable still plugged into the speedo itself. If the cause is some grease in the speedo hardening up or otherwise requiring a good service, you may break some of the internals...which is the kiss of death in some speedos or, a big bite in the butt much worse than just paying for a cleaning/lubrication of said speedo.

[Wolfman]

Key to plugging a drill into the speedo for a test run, Chuck, was " variable speed " drill.
To run the test, you start slowly and then gradually speed up.
At the sign of trouble, YOU STOP THE TEST !!!
Some discretion applied during the test. No need to peg the needle at the high end or continue if the needle starts slamming back and forth between 0 and Max.
I try not to assume ( there's that word ) but I guess I should have supplied more details on how to perform the test.

[Joe Gopan]

Age is also a factor, your speedometer is approaching 75 years, Speedometers do not have to be very old to have issues. Look in the female drive end, any signs of wear, is it still square?

[Chuck Lutz]

I think the mention of using a drill to "test" a speedo will green light guys who have found a speedo at the swap meet to start with the drill to "test" it. That may not turn out so well if they hear that is OK...

Since the speedo cable turns only ONE way....they hafta guess if it should be used in FORWARD or REVERSE mode....and I don't think turning the internals of an unknown condition speedo the WRONG way will end up without some possible fatal damage to internals.

I'd start with removing the cable from the jeep.
Then remove the inner and check to see if it is clean and well lubed and slides in/out and rotates easily.

If so, perhaps just a wipe down and application of speedometer cable lube will sole the problem.
I preferred to clean the inner with Brakekleen until the rag showed no black crud with it pulled through.
Then I held up the cable sleeve by one end and sprayed Brakekleen through it until the dirty fluid stopped and it ran clear.
Then I sprayed more into the sleeve while holding both ends up in a "U" and then with some help, ran my clean inner cable back and forth through the outer sleeve and then checked to see if it ran clear.
Once this is done....you can let it dry and coat the inner with speedo lube and run it back and forth until it is sufficiently lubed. (You may want to repeat this task as a part of your maintenance schedule rather than wait for the bounce to return).

Then with the cable reinstalled through the frame as it should be....a test drive will tell you if the problem is solved or not...either way, this maintenance is something you NEED to do.

Now you can go on to swapping out speedos with a known "good one" to eliminate the speedo from the equation which leaves the T/C. I think the T/C is the least likely culprit, the cable the most likely and the speedo what's left. Few guys have the patience, tools, skill or know-how to strip down a speedo (especially a SW) and clean and service it...and safely do that.

[Joe Gopan]

Terminology one may encounter in the G-503 TM's/SNL's.
CASING or TUBE, flexible, Speedometer Drive
Shaft/CORE.
Get out your manuals , they are educational.

[Bruce W]

I used to do a lot of speedometer "repairs", before what I was doing was rendered illegal. I never saw any speedometer that ran the opposite direction from the majority. That's not to say they don't exist, just that every one I ever saw operated in the same direction. All of those speedometers, including the ones in our jeeps, will need a reversible drill set in the "reverse" direction. Also, most, if not all, speedometers are calibrated the same - a certain number of RPM's will equal a certain number of MPH's. I don't remember now, what those numbers are, but a 550 or 600 rpm drill (yes that's slow for most hand drills) will not hurt a speedometer. BW

[Wolfman]

OK. I don't want any one to destroy a repairable speedometer because they did something I suggested.
Been doing what I do for over 50 years and I have developed some experience and common sense in that time. Still working on it, but it has improved considerably over the years.
First off, this was a working speedometer. I am reasonably sure it turns. Just jumps around and don't know why. ???
If it was a trade show find, I would try turning it by hand first. See what happens. Then considering what I saw, I would go from there.
I have spun up a lot of speedos in my time. Don't remember ever destroying one, once I was sure it was not stuck to begin with.
There was a lot of things done back in the dark ages before they were rendered " illegal".

[dpcd67]

It is not illegal to restore a speedometer and move the odometer in the process. What is illegal is to alter the speedometer from a particular vehicle and misrepresent or lie about the actual mileage of the vehicle to a buyer, or to the state. Our titles here have a block for mileage which indicates "mileage is unknown". For historic vehicles, that is the one used. After all, it is a restoration of a historic vehicle, not a real car.
If that is illegal, then so is putting a new speedometer on one.

[Wolfman]

Don't think Bruce or myself was referring to restoring anything DPCD.
Back in the dark ages, and that is when Bruce and I was talking about, it was common for unscrupulous car lots to set the odometer back on the better looking cars to get more money out of them.
Now days, that will get you put in jail if caught. As you should be.
Had nothing to do with restoring anything.

[Bruce W]

Correct in both posts, Mike. Thanks.
Turning a speedo backwards probably won't hurt it either - what happens when you back up? One shop I worked in bought a device that connected to the transmission end of the cable and ran the speedo at 120 MPH in reverse. We didn't use it much as it was too slow - In ten hours it would remove only 1200 miles. But the few times we did use it, I don't think we ever hurt a speedo.
I think the OP's problem is a lack of lubrication in the cable, and needs a proper cleaning and lube. A good inspection of the cable and casing during the operation is, of course, part of the job. BW