The Stovebolt Site Forums The Shop Area General Truck Talk speedo fault?

When driving the speedo needle sometimes shoots to the right(full speed) and theres a screeching noise.It does return to normal but can do it again.Any ideas please.

One possibility it the cable is sticking in the sheath/cover?

If that is the problem, the assembly can be removed and cleaned and cable-greased.

Mine used to do that for quite a while. A generous amount of graphite lubricant in the speedometer head seems to have fixed it for me.

Like Tim said, a sticking cable in the sheath would be an easy fix. If it is inside the speedometer itself, then you would probably need to replace. I have done some work inside the speedometer head and it is very delicate construction with small pieces. There is no direct connection between the speedometer drive and the speed indicator; a magnet spins inside a metal cup that pulls the needle against a small spring (the odometer though is direct drive). Clean and relube the drive shaft and hope it fixes it. Good luck.

Lee.

Nine times out of ten it is a dry speedo cable. Unscrew the fitting at the back of the housing pull the cable and clean it off. Lube with graphite (available at your FLAPS) and reinsert back into the cable housing. No more chatter and it will be a little bit more accurate.

I followed Jeff Erickson's instructions for "Speedometer rebuild for GM Art Deco Truck" in the Stovebolt Tech Tips.
https://www.stovebolt.com/techtips/gauges/speedometer/index.html

The squeal in the speedo of my '54 stopped and the needle retuned to normal.

The problem was a dry bushing in the speedo. Read his description under "Starting back at the base of the speedometer assembly" of his Tech Tip. He is spot on.

Warning: If you remove the speedo needle, be gentle. The shaft is very small diameter and brittle. The needle may be rusted onto it from water leaks throught the windshield over the years. IT WILL SNAP. Luckily I found out on a spare. A watch/clock maker may be able to remove it for a small fee.

It's a good time to reface the speedo and gauges while you have it out. Here is an old post about refacing my gauges. Our friends at PhotoBucket have blocked my photos. Contact me if you want them. Email in my signature line.
https://www.stovebolt.com/ubbthread...remove-gauge-face-plates.html#Post786975

Here is John Rooney's Tech Tip on "Refurbishing Dash Cluster"
https://www.stovebolt.com/techtips/interior/gauge%20cluster/index.html

Good luck with your speedo,

- Lonnie

as already stated above, normally, the speedo needle jumping around is caused by the cable binding BUT, in this case, where yours is screeching also, it is more than likely the bushing in the head. If not taken care of, one day, it will seize up and twist the cable off! (ask me how I know! lol)

You can either try to lube it, or just replace it with a new unit.

When you say the head do you mean in the instrument cluster?

Can I disconnect the speedo cable from both ends take it out and clean and lube?

Yes you can, however, you only need to disconnect the underdash end. It will be messy so be prepared to ru it through rags as you pull it out.🛠

yes.

Quite often the problem is actually a worn cable housing with rough spots where the cable/housing assembly negotiates bends. If that's the case, replacement of the whole works is the only fix. The cable hangs up on the rough housing, winds itself up momentarily, and then snaps free- - - -causing the erratic needle bouncing. The Freightliners I used to maintain for a small trucking company had the same problem with tachometer cables.
Jerry

You recommend new speedo cable?

If lube doesn't help, replace the whole assembly- - - -not just the inner cable that turns. A rough housing will shred a new cable in a hurry.
Jerry