I am trying to figure out what the issue is with my speedometer on my 63 F100. When at rest it reads below zero and when moving it seems to be 10 to 15 mph below what it should read. I have read some previous threads that touched on what might be going on but I could use some more detailed help from some folks as to what is causing this. Some additional info that may help....seems to be the original cluster, odometer and all other gauges are working, speedo cable seems to be in good shape and is fully engaged into the transmission and gauge cluster, has the original three speed non OD tranny mated to a 223. Any information/suggestions would help and let me know if you need any further info. This is my first thread, thanks everyone in advance.

 

Welcome to FTE

Look on the Warranty Plate, located on the left door face below the latch for the AXLE code. Post what it is.

At the end of the speedo cable is a nylon DRIVEN gear. It's possible someone installed the wrong one, causing the speedo to read slow.

I need to know the rear axle ratio to determine what the correct tooth count should be on this gear.

 

Thanks for the quick reply. The rear end is a 4.11 from the factory and Im fairly certain it hasn't been changed. By putting on a new/correct driven gear will this fix the issue with the needle resting below zero as well?

 

If the speedo is bouncy for the first bit at slower speeds then steadies as you go faster..speedo cable needs lube..these are accessed from inside the cab by unscrewing the cable case from the backside of the speedo and pulling off of the speedo head..the cable is right there and will slide right out...get rubber gloves as these were lubed with graphite grease originally which is what should be used on it again...a little goes a long ways...you can also look at the condition of the cable too as it could be failing/fraying...


- cs65

 

1963 F100 3 speed manual with 4.11-1 = 18 tooth nylon DRIVEN gear.

Same 16 thru 21 toothed gears used from 1960 thru the 1990's, available from Ford for less than 5 bucks.

Take your gear out, count the number of teeth.
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Bouncing speedo needle can also be caused by partially stripped teeth on nylon DRIVEN gear.

Inside the speedo cable's housing is a woven steel core, it's supposed to be lubed every so often, but most people in today's world are unaware.

When the lube dries out, the core binds up inside the housing, eventually snaps.

Autoparts stores sell a "universal" woven steel core kit. Cut it to the correct length, coat with graphite, install in housing.

 

You are correct number dummy their is an 18 tooth driven gear on the transmission end of the speedo cable. Everything seemed ok but then again I have never looked at a nylon driven gear before so who knows. I went on ahead and ordered a new one along with a new cable assembly. Both are reasonably cheap, so why not. I hope this fixes the issue when the new parts come in, if anyone can think of anything else that might cause these issues I'm all ears. Thanks.

 

If speedo is reading 10-15 MPH slow, you need to reduce the number of teeth so speedo will read faster. If it was mine, I'd try a 16 tooth gear.