FL-70 Speedo problems

[lexred]

I am new to the board and this has probably been discussed many times, but my 1997 FL-70 speedometer is driving me nuts. Most of the time it will not register the accurate speed, it is always slow, and varies from 8-15 mph off. I have changed the speed sensor and it made no difference. Several times I have cleaned the plug on the back of the unit and it might register ok for a mile or so, but then it returns to it's old tricks. I have checked all the wiring and cannot find anything out of the ordinary. Should I buy a new head or ????
Thanks
Ron

 

[greg334]

The problem may be a simple fix.

I would do this first - take pen in hand and see if you can find out where you are off. Start at 35 mph and work your way up with a watch and known distances. If it is consistently off then make sure that your tires are at the right pressure, take down the make and model of tire on the paper and talk to the dealer to set the ECM speedo correction to the right number.

Most of the FL Series trucks and the early M2s were calibrated at or near 60 mph and it will be high below 55 and lower above 63. These are not linear speedometers, never were and as much as people claim that they are right on, they are not. GPS for what it is worth is not as accurate as a good calibrated Speedo but good enough for you to measure by.

If you get a new speedo head, PM me about the old one... I need one for testing.

EDIT; I forgot to say "welcome"....