�64 Speedometer Woes - Too Slow

[Gary J.]

Tried playing around with some different speedometer gears that I had but it did not make any difference made matter worst, tried a 19, and 21. A 24 would not fit. It must be a mismatch in the transmission tail housing correct. Any ideas, want to get it corrected.
The gauge cluster is fresh looking and there is not bounce in the speedometer hand. Looking for suggestions.

[Edward J.]

[Mark M.]

[Kent S.]

[Dick W.]

[Gary J.]

If the speedo is too slow I believe you need less teeth on your plastic gear so 18, 19 should get you closer. The other variable is the diameter of the rear tire - are they stock replacement? 205/75/15 is close enough.

Kent, the speedometer gear is a green 22. I have tried a 21 that made it slower, then I tried a 19 and that made it worst. I cannot use a 24 tooth as that gear is a different diameter and will not fit.
The tires are factory sized, 6.70/15 the rear gear is a 3:70 has not been changed. The green gear is for a 3:70 gear.

[Gary J.]

Could very well be that the speedometer head needs to be degaussed. Job for forum member Joe Ray.

Dick, I may end up taking the cluster out and having the speedometer checked. I have already thought of that, the gauges in this car looks great, like a fresh rebuild, but that is not saying this is the problem. I would hate to take it out and not be the problem. It would be nice if I knew for sure if it was in the speedometer head and not the transmission. The owner is wanting it fixed, just wanting to make a wise choice. Taking the cluster out or the transmission out are not fun jobs.

[Duke W.]

[Joe L.]

Kent, the speedometer gear is a green 22. I have tried a 21 that made it slower, then I tried a 19 and that made it worst. I cannot use a 24 tooth as that gear is a different diameter and will not fit.
The tires are factory sized, 6.70/15 the rear gear is a 3:70 has not been changed. The green gear is for a 3:70 gear.

Gary------


If the gear you took out was a green 22 tooth gear, then you cannot use any gear of lesser tooth count. The green 22 tooth gear is the lowest tooth count of the gears that are compatible with the installed DRIVE gear. If you install any lesser tooth count gear, it may work for a short while but the DRIVE and DRIVEN gears will not mesh properly. To install a lesser tooth count DRIVEN gear you must install a different DRIVE gear.

By the way, the 22 tooth count gear you removed is likely the original or an original replacement. If one were to install a 22 tooth DRIVEN green gear in a transmission that had the DRIVE gear for use with lesser tooth count gears, the DRIVEN gear would be quickly "chewed up".

[Gary J.]

What tire size is on the car? Tire size has a BIG effect on speedo readings if they have significantly different loaded revs per mile than OE tires.

Speedometer error can be gain or offset type. Gain error is when the PERCENT error is about the same at every speed. Offset error is when the error is constant in MPH at any speed, and error can be a combination of both.

The GM spec is 60 MPH at 1000 cable revs, and this can be corrected by a competent speedometer shop by adding or subtracting to the flux of the permanent magnet in the head. Offset error is corrected by reindexing the needle on the pin.

...don't know where you're located, but Paul's Speedometer shop in Redondo Beach, CA, a couple of miles from my Disco Palace, can fix you up, (310) 374-3017. A local chapter member had his '57 speedo calibrated there recently. The owner's name is actually Gerd Auberlein. He bought the shop from "Paul" decades ago, and he overhauled the speedo in my SWC back in the late seventies! He drove a Dino 246 GTS back then. Gerd is probably a few years older than me, and I asked him when he was going to retire. He declined to state. He owns the shop complex where his shop is open, so I think he likes to hang around to keep an eye on things.

He's got a HUGE supply of "used" speedos if parts are not available for whatever he's working on.

Duke

Duke, I am in South Carolina, the tire size is a 6.70/15 which is the correct size for a 1964. The rear end is a 3.70 as per code stamped on the housing. I did rotate the tire one revolution and counted the turns on the driveshaft and the ratio seems correct.
Even though the cluster looks freshly restored, I am leaning now on taking the cluster out and having the speedometer checked since the tire size is correct and the rear gear ratio seems correct.

[Dan B.]

from my post on CF:

You have tried different gears with no change, the cluster appears to have been gone over recently, so my suggestion is to pull the speedo cable and directly connect a drill (running in reverse) and test it. I suspect when you remove the speedo cable, you will find a bunch of grease that has migrated up the cable (because it was over lubed when installed) and has fouled the speedo cup. If that's the case, you will have to remove the cluster and re service the speedo head to fix it.

[Gary J.]

[Owen L.]

• Do you think the original problem with being stuck in reverse is connected at all?
• How did replacing the clutch and components fix the reverse problem?
• Did the owner have the speedo problem before you got it? How about before the trans was rebuilt by whomever before you?

[Gary J.]

I'm a little hazy on a few points:

• Do you think the original problem with being stuck in reverse is connected at all?
• How did replacing the clutch and components fix the reverse problem?
• Did the owner have the speedo problem before you got it? How about before the trans was rebuilt by whomever before you?

[Gary J.]