so right now i have a 2.73 open diff rear end with the drum brakes on my 1989 firebird. things is i want a posi and dont want to change the whole rear some i have some 3.42 gears and a posi unit coming to me suppossedly from a 91 or 92 camaro. what would i need to make this work? and if i dont change the speedo gear how off will the speedometer be for this change?

 

any help because i plan on doing this this week.

 

Check your axle shaft spline count. You may 26 and the 91 parts will have 28. If that happens you are going to have a long weekend. Also walking until you put it back together.

 

342/273 = 125 so you'll read that you're going 25% faster than you actually are.

The axles should be the same # of splines. You'll have to make sure you shim the new carrier right so it doesn't whine.

 

I would not bet on the splines being the same. 1989 was the change over year and GM had a large inventory of rears were 2:73 open to use up..

 

Oh, I thought they ALL changed. Hm, well yeah then there might be a problem.


and i just realized that i forgot a decimal.. 342/273 = 1.25 not 125, lol. Same end result though..

 

interesting so basically need 28 spline if i dont already have them and shims to line it up? nothing else?

 

there's no shims used to line up the axles. do a search for my user name and sofakingdom and you'll find all you need to know

 

o no i know you dont line the axles up with shims you gotta shim the unit and gears to line up everything so it doesnt whine. i already got the shims that have been laying around.