Allright, I have an 89 firebird formula 350. Has the Borg warner 9 bolt in it, my posi has gone out. My questions are, are there any upgraded posi units for it besides just a locker? I would love to put in a trutrac, however, they don't make them for these axles, or I couldn't find it anyways. Now my other question is, I'm going to get another gearset for it, either a 3.70 or a 3.90, and have it put in at the same time, does anyone have an estimate of what all of this would cost? Mainly I wand a decent posi or trutrac for it, so if anyone has any information on any of this, it is much appreciated.

 

You could have the carrier rebuilt. New/machined cones and/or carrier ends. It also matters which series carrier you have now if you want to change the gears. There are many threads on the rebuild etc.

 

Ok, so I'm either stuck rebuilding or buying a rebuit on then, well that kinda stinks but oh well. I read somewhere that unless its a 2.77 all sets are interchangeable being that the all have the 3 series carrier.

 

Afraid so. The good news is there is a ton of info and links that will lead to everything you could ever want to know about the 9-bolt and rebuilding etc. Yes you need the series 3 carrier for all the higher gear numbers. You should be able to pick up a worn out one for not too much. I got a couple of 3.27s with worn out cones but with the ring and pinion for $60 each.

 

Base91;
you mentioned the possibility of having the carrier rebuilt. I was not aware that the 9 bolt carriers were rebuildable if they were worn out, could you elaborate?

 

They're made but they're a lot of $ from AU.

 

Depending on how worn out the carrier and cones are they can be machined to be usable if not exactly like new. If they have dug into the carrier and cone is deeply grooved by the 'step' forget it. There are threads with pictures and links to rebuilding instructions. In brief the 'step' in the carrier ends need to be removed and enough taken from the narrow ends of the cones so there is reasonable clearance between the cone nose and the carrier surface. I've got a friend who does the machining for free so that's a huge help.