ok, i have an 89 iroc z with an L98 that has the 2.77 rear end. i was told that the 3.73 ring and pinion for a chevy 10 bolt would fit my rear end. then i was told that i would have to buy a ring a pinion for a borg warner rear end. do i have a b.w. rear? all i know is it is a stock 2.77 rear end that came with the L98 and i want to get steeper gears. what gears do i need to get. thanks

89 iroc L98
new engine, less than 4k miles
!smog pump
!tb coolant
gutted airbox / ram air ducting
ported plenum
1 5/8 shorty headers
true duals 2 1/2 pipes
no cats
trans go shift kit
soon to be some 3.73s

With the 2.77 gears, you have the 9-bolt "Aussie" rear, aka: Borg Warner rear. Regular 10-bolt gears will not fit. There are a few companies that do sell gears and rebuild kits for these rears, but they are much more expensive than the much-more-common 10-bolt rears.

Another option is to replace the whole rear with another one from '90-92 with the big rear disc brakes, a posi, and a 3-series carrier/gears. As long as you have the 3-series carrier, you can easily have 3.42's or 3.73's swapped in.

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Greg Westphal
'87 IROC 305TPI/A4

What sbout swapping factory 3.73's out of an 84 drum brake rearend into a 88 formula with disc's that has stock 3.23's in it

Yep, I believe you can do that. Just have the gears swapped from one carrier to the other if the '88 has a posi and the '84 doesn't. If the '84 does have a posi, then you can swap over the whole carrier. I think it was in '89 when GM switched to 28-spline axleshafts from 26-spline, so you should be safe here. If the '88 axle does have 28-spline axleshafts, then you can only swap the gears from one carrier to another...

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Greg Westphal
'87 IROC 305TPI/A4

You can only do that if the 88 has a 10-bolt. It probably has a 9-bolt, in which case the 10-bolt stuff from the 84 won't work, as described above.

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"So many Mustangs, so little time..."