i swaped my blown 700r4 out of my 91 b4c with a th400 out of a 1989 c2500 truck. the speedo plug in is the same as the 700r4 but it is way off. The speedometer will spike to 145mph and stay there at about 5mph(guess), then return to 0 when i stop (bounces back and forth in stop and go traffic)

what do i need to do to get this close. do i need adapter??


thanks

anyone ever have this problem?

ttt

You need to change the reluctor ring in the tranny to a plastic speedo gear.

Considering they are both electronic Vehicle speed sensors, you just need to swap the one from the 700r4 to the TH400. The 1989 TH400 truck transmission VSS sends out a different number of pulses per mile than the 700r4 in the F-car does. The 1989 truck had RWAL or Rear Wheel Anti-lock, and outputs 128,000 pulses per mile vs. your 4,000 pulse per mile.

The one from the 700r4 won't fit the 400 trans (too big)