Changing the speedometer gearing will solve your problem if your test results are something like this:
actual MPH ......... 20 25 30 35 40 45 50 55 60
speedometer reads 23 29 35 41 47 53 59 64 70
You've already done the 35 MPH test, just do two more, maybe 25 MPH actual and 50 MPH actual.
Last edited by Bill Hanlon; 08/17/2026 2:46 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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