Speedo in op on 4 speed OD trans.

airkiller said

So I take it that for any given pinion gear there is only one location where the gear will mesh with the trans shaft and that is the ratio you have.

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That's right

airkiller said

I have P225/60R 15 tires and they are approx. 25.5" in Dia. and the rear end is set up with 355 gears. What speedo gear pinion do you think I need?

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Here's a chart from year one:

http://www.yearone.com/pco/1_0210/full.asp?page=395

It shows you need a 36 toot speedo gear

Believe me, this is easy stuff. Mopar is the only manufacturer, that I know of, with easily swappable gears like this, because of the eccentric plug. Ferds/ GM have a press-on gear on the trans mainshaft, which will support one, maybe two different speedo gears, then you have to tear down the trans and press on a different speedo gear. !!! PITA !!!