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Speedometer wobble...

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bt7tricarb

bt7tricarb

Senior Member
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O.K. - now that the trafficator issue has been raised, I'll start with a new one...

During the restoration, my speedometer was sent out to be re-done. None of the faces of the guages seem to have been re-silkscreened, but that's another topic.

Two things on my speedometer now.

1. The speed is fairly accurate up until close to 60 MPH, then it's significantly off (as much as 8 - 10 m.p.h. when over 65 m.p.h. - ex. - when my speedometer shows that I'm close to 80ish, I'm only going 72). I did have my OD changed from 20 - 28%, but I thought the shop owner that did my car told the person who went through the guages this information. Is this just something most everyone experiences?

2. The gauge still has quite a bit of "bounce" to it. Instead of being nice and steady, the needle bounces between anywhere from 5 - 10 miles an hour, degree wise (i.e. - if I'm going 60, according to my GPS, then the speedometer will "bounce" between 55 - 65). Does anyone else experience this? I just thought that on a rebuilt guage this would not be an issue. I also wondered if it could be something in the cable...
 
There might be something with the cable. First would be to lubricate it. There may also be a kink in the cable which is causing it to bind. Also, check out Dave Russell's reply here
 
Greg has a good starting point. Check the inner cable by removing it & rolling it across a flat surface. If it doesn't roll smoothly but has a "jump" in it, it should be replaced.

The outer cable must be positioned with no sharp bends, kinks, or pinches in it.

Sometimes the inner cable extends too far into the speedometer head & causes binding. The inner cable as measured from the face of the outer housing to the end of the inner cable should be no more than 3/8". You can get a rough check for binding by unscrewing the cable housing to speedometer retainer nut a couple of turns & pulling the cable & housing back a bit to see if it helps. If this works, you can carefully remove a bit from the end of the inner cable.

In rare cases, the speedometer gear box on the transmission has problems. Where this drive connects to the back of the transmission, there is a very very short square section cable that can get damaged. there should be a copper washer between the cable attachment & the transmission drive spigot. If the washer is omitted, the drive can bind. Item #17 here:
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28941

The OD ratio has no effect on speedometer calibration. Only axle ratio & tire size affect the calibration. This is because the speedometer drive is on the output side of the OD.
D
 
A new cable was installed and:

- Speedometer is smooooooothhhheeee!!!!

Thanks to all who replied. I did suspect the cable as the "bounce" I was experiencing did seem like "mechanical" - if that makes sense. It was is if something was binding up and then releasing suddenly - over and over and over again.

But with the new cable, there is no problem.

More questions soon.
 
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