Read all I could find in the search, so I have a clue, but would like some confirmation.
My speedo sticks at about 20mph, even when stopped. At about 40 it breaks loose from the 20 spot and seems to work OK above 40.
It makes no noise and doesn't fluctuate, once it starts working. I haven't pulled it yet, but I can't see any "oil" hole from standing on my head.
Will there be one on a 54 F100?
Does this sound like something a little oil might fix? Or should I plan on a full teardown, cleaning, etc.? Thanks,

 

Don't use oil, use speedometer lube which is just plain graphite. Oil will make a gummy mess. The only way to lube it is to disconnect the casing behind the speedometer, pull the cable and pour some lube down the casing, working it in with the cable. It's best if you pull the entire casing and clean it out to make sure it's not gunked up and reinstall it. Graphite's a mess but it's the best thing to use.

You might only need to re-lube it to fix your problem.

 

Bob, I don't think it's a cable problem. It's not irratic or noisy, I think the mechanism is sticking in the head. I've read about using a light lube on a felt pad somewhere in the back of the head. It's not clear if this applies to a 54, or where to find it.

 

one way to maybe find out if it's the speedo or somewhere below is to unhook the cable from the speedo, pull it out from under the dash to a position where you can keep an eye on. drive and watch the end, see if it does anything weird? might work. dick r

 

All mechanical speedos work on the same principal so knowing how they work may help locate the sticking spot. The cable drives a rotating magnet in the head. That magnet pulls on another magnet on the needle shaft. the needle's rotation is resisted by a light coil spring like a watch spring. The faster the first magnet rotates the further it pulls the needle around. It happens fast enough that the needle appears stationary. The usual culpret for the symtoms yours shows is a needle contacting the face of the gauge due to a bump or warped gauge face. A weakened or gummed up spring is the second likely issue. A dust ball or even an insect may have gotten wedged in the spring. The two magnets making contact may be a distant possibility.

 

Pulled the speedo. Basically fine. Had some corrosion on the watchspring, soaked it with penetrating/lube. I think the corrosion was making it hang up. Also lubed the felt packing. reinstalled and it works. Bounces a bit below 20, don't know if thats normal, or still a bit of dragging from the rough area of the spring. Now that it is free to move, it should get better.
Thanks for the help.

 

hades at least yours works !! i got three of them including the one in it that quit and 1 good one left if i use oe gauges when it goes back together .

 

I had some voodoo speedo problems in a datsun. The first problem was the stupid cable would vibrate around and eventually kink. This would take a couple days to couple months after fixing it. After finally getting the mounting tabs situated the problem occured again, this time from the speedo gear in the tailshaft which got worn.

Whether it was the kink and/or the gear, at the different times the speedo would bounce until 40mph or work fine except read 20mph till 35mph or a combo of both. I assume a kink would cause a bounce, and the faulty reading from the gears slipping.


Check the cable for any kinks. Overtightening a mounting tab can also put slight strain on the cable. Both of these will hold the cable slightly till the tranny side overcomes and thus the speedo bounces as the cable catches up. This could also be caused by either a lack of or contaminated lube in the cable.

Since this is a reoccuring problem I had I would pull the cable and do a hostpital like cleaning and lubing operation. At the same time inspect both gears in the tailshaft for damage and lube them on install. The Datsun mounting tabs were turning with the vibrations causing the kink. If you got thread locker lying around, it wouldn't hurt to add them to the mounting tabs if it looks like they could be kinking.

It's no fun when you lose the function of your speedo. A slight bounce will get bigger and bigger wearing out your gears and cable.