I bought a Instrument cluster at the wrecker today. It goes to 100 which is cool. I'm replacing the one in my 77 which only goes to 85. Will it read the correct speed without any modification or calibration??It's a 1977 150 4x4 4-speed. Thamks,Don

 

you can switch out the speedo/odo part of the speedometer. just unscrew the back of the case and i think theres two little bolts that hold the speedo in place. this doesnt answer your original question, which i dont know the answer to.

 

Yes it will register correctly.
The ONLY change in speedo speed operation is the gear that goes into the tranny.

All speedometers are.... is rotation measuring device depending on the speed of the inner rotating cable.

They are all calibrated to the same spec.

 

=1000 revolutions per mile.

 

Thank you very much!

Don

 

I did it on my 79, no problems, easy swap.

 

i dunno where this would go but FYI, my insturment cluster out of a 74 f250, the place where you plug in the main wire harness would not fit in my 77 f150. so i am assuming the backing plate and circuit board are different for those models, because the speedo out of the 74 does not have the high beam indicator above 50mph, it is over on the side where our brake and seatbelt lights are. I put the 74' speedo in my 77 and the high beams still work there is just no indicator because it is suposed to light up on the speedo

 

Good point !

The transition time for this was 1975

 

I had the same problem with the high beam indicator, I just drilled a 1/4" hole at the top of the speedo. Simple enough and most people don't know the difference. I think the 100 mph speedo's with the "cut out" already in them were only made in the early part of 77.....I could be wrong though.