Topic: Re- calibrating speedometer, can it be done and how to?

[GroovieGhoulie]

My speedo is erratic between 60 and 70 and is not reliable over 75 or so.  Is there a way to recalibrate it to bring it back in line?

[Bob Wessner]

When you say erratic, do you mean wavering, not steady? If so, maybe cable needs lubing, new cable or it's not routed well and has a kink in it??

[cb(r)]

ya check all possibilities before opening up your tach or speedo. they are not hard to open but if you do not need to then dont!

[GroovieGhoulie]

When you say erratic, do you mean wavering, not steady? If so, maybe cable needs lubing, new cable or it's not routed well and has a kink in it??

It reads fine up to 60, then it stops, but the RPM keeps climbing, then it jumps to 70 and keeps climbing. Then, in general, I doubt its accuracy over 75-80.

I'm getting a GPS to confirm my true speed compared to the speedo as I want to know how close I am to the ton.

Up to 60, it seems to be dead on.

[csendker]

If you have/get a spare speedo, change it out to see if it's the gauge or not.  Then try swapping the cable, etc. until you find the culprit.

[DrMark]

I would try a spare speedo first. It almost sounds like a bad spot on the internal gears....had that happen on my Buick. Lube cables like the others have said.

[bistromath]

Probably a dry/worn spot on the bearing that the needle and eddy cup rotates on. If so, you can open it up (read the FAQ) and re-lube it with a very very small spot of lithium grease.

[crazypj]

Probably a dry/worn spot on the bearing that the needle and eddy cup rotates on. If so, you can open it up (read the FAQ) and re-lube it with a very very small spot of lithium grease.

It has no internal gears for the speedometer, the gears are for the mileage counter.
PJ

[bistromath]

Probably a dry/worn spot on the bearing that the needle and eddy cup rotates on. If so, you can open it up (read the FAQ) and re-lube it with a very very small spot of lithium grease.

It has no internal gears for the speedometer, the gears are for the mileage counter.
PJ

Where did I say gears? There is, of course, a center bearing that the needle rotates on.

[WHALEMAN]

What drives the needles on both the tach and speedo is a circular magnet that is spun by the gearbox on the rear of both units. This circular magnet drives a steel case that fits around the magnet. The gap between the magnet and case is in the neighborhood of 1/32nd inch. As the magnet spins it turns the steel case against a spring and changes the speed or rpm in a lineal correlation to magnet speed. What happens is there is a bushing between the gearbox and the spinning magnet. This bushing becomes worn. As the RPM of the magnet increases small balance factors come into play and the magnet will wobble and touch the steel driven case momentarily changing the case output to the needle. At slow speeds nothing touches. As the bushing becomes very worn the needle will wobble constantly at any speed over 40. I have heard there is someone that knows how to tighten this bushing and stop the high speed jumping around. I have tried to open the case clean and grease this bushing and it works for a while. I know of no other way to stop this wobble.