Speedometer pinion year

[bc3j]

I've seen many charts about the speedometer gear vs diameter, but they all contradict the FSM. I am using 235/60-15 tires all around which is nearly identical to E60-15s in diameter and revs per mile. Both 26.1 diameter and 235s 772.65 revs and the E60s are 773 revs. My FSM shows the gear to be a 34 where the online charts show 33. Just like to hear your thoughts from your experience with this. I've always used the FSM as more or less gospel. Story about the title. System won't let me edit.

[Cuda Cody]

I would trust the manual first. 

[6bblgt]

Chrysler actually changed the speed-o pinion for E60-15s between 1970 & 1971

1970 * 3.23:1 & E60-15 = 34 teeth
1971 * 3.23:1 & E60-15 = 33 teeth

[bc3j]

Thanks. Interesting what the factory did. Curious, a mid season change perhaps?
Thanks again.

[6bblgt]

1970 * 3.23:1 & E60-15 = 34 teeth - my '70 383 R/T (mid-July 1970 build)
1971 * 3.23:1 & E60-15 = 33 teeth - a '71 340 Challenger (early-August 1970 build)

[7212Mopar]

1973, 3.23, 33 teeth.

[bc3j]

Chrysler actually changed the speed-o pinion for E60-15s between 1970 & 1971

1970 * 3.23:1 & E60-15 = 34 teeth
1971 * 3.23:1 & E60-15 = 33 teeth

Thanks for the info. I've got a 1970 with a 3:23 and a January 1970 build.

[bc3j]

Finally got the 34 tooth gear in and the speedometer is right on with the GPS. Thanks for the info!