[rich weyand]

On the K trucks, the speedometer accuracy was achieved with a limited selection of gears for the transfer case (NP203 or NP205), and a ratio adapter to correct to 1000 revs per mile. On the C trucks, there were a lot more speedometer gear choices, at least for the automatics, and the adjustment was made in the gears. Not sure about the sticks.

86C20: I thought you had 3.42 gears in the hillbilly? It would be a lot easier to figure out what you needed if we had a baseline -- some reading like it's 12.5% slow -- but with no connection at all it's difficult. 4.10 gears with what tire diameter? Speedometer driven gears ran all the way from 16 to 25 teeth in one-tooth increments depending on ratio and tires.