The Stovebolt Site Forums The Shop Area General Truck Talk Speedo needle bounce

About 10 years ago I was finally able to source the trans gear to activate my speedometer. I replaced the broken head with a good used unit, new cable and housing. My problem today is the needle is fluctuating 20-30 mph, sometime settling on a average speed. 1946 half ton with a 4 speed trans. I am familiar with old mechanical speedos chattering when the cable needs lube, is this the same issue?

I like to use Lubriplate white lithium grease on a speedometer cable. If there happens to be a tight bend anywhere in the cable housing, it's possible for the inner cable to wind up and snap forward repeatedly, causing a chatter of the speedo needle.
Jerry

I find I can overtighten the cable at the speedometer and it does crazy things. I then back off a smidge.

Mine bounces terribly. Do you disconnect completely and then clean and lube it?

Most drive cables can be pulled out of the housing from the speedo end, no need to disconnect at the transmission. Give the cable a good wipedown with a solvent-soaked rag, and coat it with fresh lube as you reinsert it into the housing. If that doesn't improve things, and there's no tight bends in the housing, there's probably some roughness inside that the drive cable is hanging up on.
Jerry

The two easiest things to do are clean & lube as Jerry recommends and not over tighten the connection as the speedometer as Wally noted. Either or both of those can make the needle bounce. My experience has been that a lube issue usually presents as chattering as well as bouncing. While I've not personally experienced it, I've been told by a speeo rebuilder that a worn/damaged drive gear can produce bounce as well.

Tiny I think over the miles the cable wears a trough in the housing that can get dry and chattery. If you recall there used to be an old guy at the swap-meets that had a display of a smoot running speedometer,he sold a special lube for them . Mine runs OK but the hand rubs on the glass,at about 50 it's pretty smooth for 71 yrs. Also the 2-speed switch-over is fine.

JW51 do that then run it carefully with your battery drill from below to see if it's smooth.

We used to have a tranny guy that would come and assemble your clean automatic transmission,he seldom missed. He commented that graphite wouldn't work on the speedo cable,chatter.

So here I am a month later! I posed my original question because I was familiar with old speedo cable chatter and some slight vacillation when the cable needed lubrication. My needle was waving at me! A bounce that would vary to about a 50 mph spread and it became worse to the point that the needle pegged to max and back. I agreed with everyone suggesting lubrication, but was just sending out feelers for other possible issues. Having been in the business, I still have a half-used one gallon container of Lubriplate and finally got off my butt. The housing was so dry, that lubed the cable 4 times, back and forth until it went back in. SUCCESS!! Thanks for your input.

46 Texaco On my shelf is a half used I think 1/2 gallon can of lubriplate that is so old the can is an antique. Need to get it down and grease mine too. Also have a 5 lb. roll of dutch boyrosin core solder half gone has the dutch boy right on it. I thought the other day maybe it is gonna get me thru !!

I've been told that graphite will actually make the problem worse.

While we’re talking about removing the speedo cable for maintenance, what size brass knurled thumb nut do I need to buy for the actual speedometer? I’ve read where they make the job of taking the head out and reinstalling it much easier. Thanks

Chuck, if you have the speedometer removed from the truck it is not difficult to remove the speedometer mechanism and clean and re-lube it. A few years ago I posted instructions on how to do this. The main and most important thing is to be really careful removing the needle. The needle may not want to come off and you may break the shaft removing it. You can isolate the needle with very thin pliers or a hemostat, but even doing that won't guarantee you can avoid problems.

But then I came back and explained with images how you can repair/restore that broken shaft using easy to find brass tubing from K&S Co. Sadly we're not adding to Tech Tips these days, but maybe you can find my post on repairing the shaft and oiling the speedometer. There is also a post I made on renovating the odometer wheels (along with free printable images you can use with waterslide decals or double-sided adhesive) and instructions on how I do that.

Most of these speedometers don't seem to be worn out nearly as much as dry and lacking lubrication. The ones I've seen simply need to be revived a bit. Sorry, but I can't recall offhand the size of the thumb nut. Offhand I think it is 5/8"/18 thread at the speedo head but you should check me on that.

I use 10/32 knurled nuts on my instrument gauges.