So I have a '91 Firebird project. As it's slowly coming along, I've definitely decided that the plain jane drum brake, non-posi rear end in it is gonna = no bueno later on when I start getting to the fun stuff.

I was curious if all rear axles in third gen cars are essentially the same? Specifically, I'm wondering if one off of an '85 will work on a '91? Do they use the same disc brakes as a posi axle off a '91 would? And I know there are both 10 bolt GM rear ends and 9 bolt Borg-Warner rear ends that came on these cars. Is a 9 bolt a good idea if I'm planning an LT-1/T56 swap later on? Or should I look for a 10 bolt? Thanks in advance!

 

82-02 all bolt in using the same panhard, torque arm, trailing arm, spring, shock attachment points.

82-97 drum rears have 3-bolt housing ends
82-02 disc rears have 4-bolt housing ends

82-92 are a narrower width
93-02 are wider

82-99 10 bolts have all the same bearings & seals

82-88 10 bolts are most all 26 spline axles
89-92 are part 28 spline, part 26
93-02 are all 28 spline axles

82-92 are part drum, part disc production
93-97 V6 are part drum, part disc production; V8 are all disc
98-02 are all disc

82-88 disc rears are iron calipers & small rotors
89-97 are PBR alum. caliper & bigger rotors
98-02 are different alum. calipers, bigger rotors w/ internal drum e-brake

I don't know of any differences in u-joints that would impact your swap.
E-brake cables are another item which may vary and you'll want to research.

You could get a 9-bolt because it's stronger or you could get a 10 bolt because it's cheaper to rebuild and a spare is easier to find.
Corrections welcome.

 

Wow, lots of facts there!

Hmm, yeah, I was told the 9 bolt rear ends are stronger than the 10 bolts, but that parts are more expensive for them, due to availability.

What are the differences between 26 and 28 spline axles? is it possible to use larger rotors on an older rear? And what role does the number of bolts in the housing end play? Are most rear ends a direct, bolt in swap? or are some mods necessary?

 

Strength. A few 28's found their way into 89 cars (10-bolts), but for the most part 90+ cars were equipped. All 9-bolts, BTW, were 28 splines.

Not without modification.

Simply the difference between drum and disc axle flanges.

Yes.

The following link may will provide answers to other issues, such as combination valve, speedo, and parking brake, as well as general info about the third- and fourthgen rear.

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC