Road test your car on the highway to check the odometer's accuracy against
the speedometer highway markers.
Check the TPM (turns per mile) number on your gauge (ie 980, 100, 1325) .
The TPM number shows the amount of times that the cable will rotate in one
mile.
To check how many tpm"s your cable is doing you must first mark 58.80 feet
(1/100 of a mile) on a level surface. Remove the speedo cable from the rear
of the speedometer unit. fit a cardboard counter on the inner flex of your
speedo cable . count the number of turns the counter makes when you push the
car the marked distance of 52.80 feet (52 feet 9 1/2 inches) Then multiply
the number of turns by 100. this number should equal the TPM number marked on
your speedo face plate.
If the TPM number does not equal the turns of the cable, your problem could
be: incorrect speedo gauge for vehicle, incorrect tire size, incorrect
wheel size, incorrect rear axle ration, faulty at cable drive end, drive that
is on/or to the main shaft is faulty.
Check for a kink in the inner flexible shaft by rolling in on a clean flat
surface.
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British Car Specialist 2060 N. Wilson Way Stockton Ca 95205
209-948-8767 Healey Doc@aol.com
Norman Nock - Tech, advisor, David Nock - Service
Sheila Huggins - parts locator
Technical books by Norman Nock avalilable for the MG and Healey.
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