The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Crazy speedo on my '63

My speedo is great up to 40 mph, then bounces al around when I drive any faster. Some people advised me to get it rebuilt, magnets were bad.
So this past weekend I rented a ditch witch, and pulled it on a trailer, and I noticed my speedo was rock. Solid, steady and accurate. When I returned the rented equipment, while driving home my speedo was bouncing again.
Any ideas why a load would make it act normal, then no load it bounces? Thanks for any help

Try the easy part first. Disconnect the cable from the spedo,
remove the inner cable and apply some white grease or a suitable light lubricant. It could very well be sticking in the housing causing the problem.
Fred

If lubricating the cable doesn't help then you will also need to lubricate the gears of the speedometer itself. The cable is the issue in a lot of cases though. No sure why having a load would make any difference.

Thank you, I should have added that the cable is new, well less than 3 months old as well as the drive driven gear in the side of the trans. I will try some lube on the speedo gears. But today I pulled a small trailer with a 4 wheeler and again the speedo was perfect,dropped off the trailer, and driving home speedo bouncing all over the place above 40 mph. Would clutch slippage cause this?
The truck had no trans when I bout it, I located a used 3 speed from a salvage
Yard and dropped it in, using the existing clutch that was in it for many years. I do hear/feel it slipping if I really push the pedal especially in 2nd gear, and that is when the speedo goes crazy. Just a thought

It very well could be a clutch slippage issue. If you are taking it easy with it when loaded and not slipping the clutch that could explain the situation. If you are getting on the gas much more when empty and slipping the clutch, then yeah, I could see the inconsistency. I would address that clutch issue first, that's the primary issue to fix first and that will tell you if it's related.

The speedo cable is attached to the tail shaft on the trans and a slipping clutch should not affect it at all, the new cable could have sat on a shelf for a long time and the lube got hard. Clean the inner cable and spray some brake clean thru the outer cable, blow it out and relube it. Remove the speedo and blow it out gentle with low pressure, it could possibly have dust and crud inside it ( remember it is over 45 yrs old). Good luck.

No way does clutch slippage cause this problem.

The big money is betting you don't have the cable routed properly and it's binding under normal driving conditions and when under load/torque it's not.

Check the cable pathway. Also is it a one size fits all cable? They are notorious for this.

Assuming that greasing up the link doesn't help then you will moreover should grease up the rigging of the speedometer itself. The link is the issue in a great deal of cases however. No beyond any doubt why having a burden could have any effect.

Any chance the cable is installed in a manner which creates a bind on it when there is no load and changes position when there is weight on the suspension? You mentioned the cable is new. Did you tie it up to anything between the dash and the tranny?