How rare are the Borg Warner 9 Bolts?

I bought a 86 TA years ago for the posi rear. I had a shop swap it out for me about 5 years ago.

Last night I went to service the rear and found out my new cover want fit. I was like WTH i dont understand. But i did notice the other night working on my torque arm that the rear had a borg warner cast on it.

So last night I googled BW camaro rear. Well there it was 9 bolt rear. I never knew of these

How rare are these things?

 

Short answer - they're not rare.

They were put under a lot of IROCS/trans ams/GTAs/Formulas (I may be wrong on some of my firebird assumptions but anyways...) They started putting them in around 86...I think?

They are stronger than the factory 10-bolt but parts are more expensive (as they are kind of a sole-source deal).

 

There are many many threads on the 9 bolts and what it takes to rebuild them but if you're not going to do it yourself it could get very expensive. Usual advice is to get a 10 bolt because parts are cheaper and easier to get. 4th gens also have 10 bolts and sometimes better posi units but the axle is wider so that's another issue.