Speedo reads low 1972
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Intermediate
Joined: Apr 2005
Posts: 44
Likes: 0
From: Vancouver BC
Speedo reads low 1972
I just had my speedo out to replace the plastic drive gear for the odometer.
The odometer now works and I have clocked it over a measured mile and it is accurate.
Prior to taking it apart it the speed was accurate, now after putting it all back together the speedo reads approx 10-15 MPH low.
I hate to have to remove the thing again but will if anybody has any idea how to reassemble it so that I get my accuracy back.
I tried adjusting the speed by turning the cross piece on the rotor to form a "X", I hooked up a drill to the input and ran it at 60 MPH, I reached 1 mile in 50 secs, ran it at 50 MPH and reached 1 mile in 1 minute, so that confirmed it was indicating approx 10 MPH low.
That was the best I could get, had that thing apart 8 times trying to calibrate it.
The needle is on a fine coil spring and it's driven by a a magnetic pick up.
Any instrument experts out there?
The odometer now works and I have clocked it over a measured mile and it is accurate.
Prior to taking it apart it the speed was accurate, now after putting it all back together the speedo reads approx 10-15 MPH low.
I hate to have to remove the thing again but will if anybody has any idea how to reassemble it so that I get my accuracy back.
I tried adjusting the speed by turning the cross piece on the rotor to form a "X", I hooked up a drill to the input and ran it at 60 MPH, I reached 1 mile in 50 secs, ran it at 50 MPH and reached 1 mile in 1 minute, so that confirmed it was indicating approx 10 MPH low.
That was the best I could get, had that thing apart 8 times trying to calibrate it.
The needle is on a fine coil spring and it's driven by a a magnetic pick up.
Any instrument experts out there?
Pro
Joined: Oct 2003
Posts: 641
Likes: 2
From: Storm lake Iowa
I don't know of any way to accurately calibrate on the bench without the right setup...the little bar that adjusts tension on the spring is VERY sensitive, small changes can result in large chages in your speedo reading. Your approach with the drill would work in theory, and you'd eventually get there by trial and error, but as you've learned that thing is a PAIN to remove and reinstall for road testing. I'd send it out for calibration if you want it accurate...I had vetteinstrumants@aol.com (he's a forum member, can't recall his handle though) do mine, very reasonable price, friendly, quick.
