I am changing my 3.23 out for a 3.42..... what do I need to get to correct the speedo reading?(part numbers would be usefull) How far off will I be untill i remedy the problem? Also, how can I make sure that this ring gear and pinion are infact a 3.42 set? I have never been screwed on the classified board here as of yet, but i would like to be sure before the damn thing goes in.

 

Change the gears from 17/41 which you have now to whatever an auto / 3.42 f-body would have. I don't like the online gear calculators; seems like they all give different tooth counts than what GM put in cars. So if a G92 / Auto / LB9 1988 IROC got 3.42 gears, see if el dealer de GM parts can look up that car & buy for it. I don't remember what tooth count gears I pulled from my 700 which was in a car w/ 3.42s.

Barely.

Count teeth. Divide.

 

What jmd said. I switched in 3.42 from 3.08 and it is barely off 5mph.

 

ok cool... thanks