I finished my first swap. An 89' 2.8 multiport replaced with a 350 TPI along with the tranny, posi rear, and gauge cluster. Everything runs great except the speedometer is running about 10% fast. Is there a sending unit of some kind between the speedo cable and the gauge cluster and if so where do I find it.

 

when you put the posi unit in, where the gears the same our were they bigger gears. mine speedo was off +10 mph when i went from 3.08 gears to 3.73. If thats the case then you have to get speedo gears with the right amount of teeth on them to correspond with the new gears you have.

 

The posi rear was a different ratio but I swapped the tranny, rear, and gauge cluster with the 140 mph speedo(original speedo was 120 mph). So wouldn't the speedo gear have been changed with the tranny? I just disconnected the plug from both tranny's and left the wires in the car then replugged them when I put the new tranny in. The donor car was all original but I had no way to check the speedo because the car was wrecked and not drivable. I think there should be some kind of sending unit or something that needs to be changed with the gauge cluster but I don't know where it is at.

 

are you useing a 4 out buffer?

 

I have no clue I don't know what that is

 

the 4 out butter is a little yellow biox that is piggy backed on the older ECM's it runs the speedo. i hooked it up to my 305 when i did the v-6 to v-8 swap and it was onlt 1-2 MPH off when i had it tested on the dyno. from what i have been told it will redo the math on its own even if you swap out the rear end..... again i could be wrong... look up some into about the 4 out buffer on the boards and see what you come up with.