Speedometer repair

[lbuch40]

I reviewed the older posts about this, but couldn’t find the answer my specific question.
The odometer works, but counts slower (less miles) than reality. This doesn’t bother me as much as the speedometer bounces around erratically but usually stays fairly consistent ay highway speeds, but about 15 mph slower than reality.

My main question is, can the disc magnet and cup on the speedo mechanism be repaired by myself on the bench? Can parts be purchased?
Secondly, what are chances the issues with the odometer and speedometer are inter-related?
I realize eventually I will need to replace the cable with the correct tooth count to fix the odometer issue.

Thanks in advance for suggestions.

 

[serial car restorer]

Bouncing speedo needle is usually a bad cable. The slower speed reading and odometer are both related to the world gear for the size of your tires and axle ratios.

 

[Broncobowsher]

Odometer reading low goes with speedometer reading low. It is a gearing change. Not only axle gear, but there are different speedometer gear ratios. Pull the speedometer cable out of the transfer case and count the number of teeth on the gear. you will need a gear with fewer teeth. But 16 tooth gears are the smallest they make. If you are running too tall of a tire for the axle gearing, you will reach the limit of not enough gear option.

 

[chuckji]

Wild Horses has an informative write up on speedo gears.
https://www.wildhorses4x4.com/early-bronco-speedometer-drive-gear

 

[lbuch40]

Thanks for all the thoughts. Will order a new cable and driven gear. (mine has 19 teeth ). Will shoot for about 10 to 12 % reduction.
Hope this also solves the bouncing speedo.
I see new cables come with the housing outer shield. Any good reason not to just slip the new inner cable through the existing housing?

 

[serial car restorer]

If the old housing has a rough spot inside, or is kinked, the new cable may still cause speedo bounce. It's more work to swap it complete, but more likely to fix your problem.

 

[lbuch40]

So…I replaced speedo cable and dropped the gear tooth count from 19 to 18. Based on 28” tires and 3:55 gears, 18 should be about right.
Speedo needle is not bouncing now, at least as bad as before. But, both the speedometer and odometer are still reading slow. Speedometer reads 50, when actually going 60-65. And odometer is reading less miles than actual.
Any other ideas?

 

[Broncobowsher]

Are you running 28" tires? Or something larger?

 

[lbuch40]

Are you running 28" tires? Or something larger?

28” yes.

 

[EPB72]

28” yes.

and are sure about the gear ratio? unlikly but possible nthe gear on the output shaft is slipping but i think that maybe erratic as well.... have you looked on the classy gauges site : sponser here} he has parts he sells as well as repairs and complete restores,he shows a speedo clockspring relativly cheap, ,,, the new cable is lubricated correct alot are not out of the box ,,,

 

[lbuch40]

and are sure about the gear ratio? unlikly but possible nthe gear on the output shaft is slipping but i think that maybe erratic as well.... have you looked on the classy gauges site : sponser here} he has parts he sells as well as repairs and complete restores,he shows a speedo clockspring relativly cheap, ,,, the new cable is lubricated correct alot are not out of the box ,,,

Will definitely check out the Classy gauges site.
I checked the gear ratio by taping a string to the drive shaft and counted the number of wraps after rolling the tire one revolution.
I did lube the cable with graphite before installation.

 

[Broncobowsher]

It doesn't make sense. A 16 tooth will get you the closest, but that still isn't right. You should not need that few teeth with that small of a tire.

 

[lbuch40]

Will definitely check out the Classy gauges site.
I checked the gear ratio by taping a string to the drive shaft and counted the number of wraps after rolling the tire one revolution.
I did lube the cable with graphite before installation.

Is the speedo clock spring and / or other parts of the speedometer head relatively to replace for a DYI guy? Any special tools needed?

 

[thegreatjustino]

Is the speedo clock spring and / or other parts of the speedometer head relatively to replace for a DYI guy? Any special tools needed?

https://classicbroncos.com/forums/ams/speedometer-rebuild-101.572/

 

[lbuch40]

Thanks for this link. Gives me a pretty good idea what’s involved. I have a suspicion that the speedo spring is what may need replaced. This article doesn’t really get into that, but I think I can get that far and see what things look like inside and go from there.

 

[lbuch40]

Talked to Kevin at Classy gauges. Pulling out the gauge cluster and sending to him for a rebuild.

 

[EPB72]

Talked to Kevin at Classy gauges. Pulling out the gauge cluster and sending to him for a rebuild.

He can tell you if it’s out of calibration before rebuild ? Just curios ,,

 

[SeaVee]

He redid mine,looks great but haven’t wired the truck yet. He knows his stuff for sure

 

[lbuch40]

I agree. And very pleasant to deal with.

 

[lbuch40]

He can tell you if it’s out of calibration before rebuild ? Just curios ,,

The speedometer? I don’t know. In my case, I know it’s not right. But give him a call. He can tell you everything you need to know.