i want to change the differential on my 89 transam 305 tbi but i'm not sure which axle spline i have. i heard that you can find out by the vin number, which number would that be? btw, i'm getting slp posi. i also heard that you need an install kit? where would i get that?

 

Its pretty likely you have 26 spline axles but to find out for sure you have to take it apart and look and count. The SLP posi is for 28 spline axles so in order to use it, you'd have to upgrade your axles at the same time. Find a local gear install shop and pay them to do it. Installing gears is not something anyone can do in their garage. It takes special skill, knowledge, and tools.

 

88-down is 26 spline.

89-up is 28 spline.


I second the tools part. If you're mechanically inclined, you can do it, but it's not the best idea to go it alone without having done one before.

 

hehe obviously i wasn't even gonna touch the rear end at all, i have a mechanic that my parents have been going to for years, a good guy, he'll be doing it, i just want to make sure which spline i have before i go order the slp and find out it doesn't fit.

 

89 is the changeover year. There's no way to know what the factory put in there, much less what's there now, except to pull the cover and look.

It seems that about 75-80% of 89 cars have 26 spline, the rest 28. The real common ratios (2.73, 3.08, etc) seem more likely to be 26 spline.

It's not in the VIN.

Tale off the cover and look before you order anything.

For a kit, try www.drivetrainspecialists.com

 

If it's a 9 bolt rear end, the axles are 28 spline.

Miles

 

And where did you get this info? I'm going by the people on this board, and not once have I heard of an 89 10-bolt having 28 spline axles. Its 89 and older with 26 spline and 90 and newer with 28 spline, in 10-bolts. But there could be some 28 spline '89 rear ends out there, I just havent seen or heard of any, yet.
All 9-bolts already have 28 spline axles.

 

I ripped it straight out of my ***, still covered with ****. That's also the year break for 28 and 30 spline 8.5" axles.