89fbrestor

first post, new to the site and new to the third gen cars. just bought an89 firebird. i love it, my question is will a 74ish to 78ish z28 3:73 rear fit in my 89 firebird? my firebird is all stock from what i can tell. vin # e witch i was told tells me it's the 305 and probably 2:79 rear. if i sound stupid forgive me i'm new at this would i have to modify anything? i have a crate motor being built with around 350 hp and i would like to have a beefier rear in the car before it arrives. and would anyone know what trans i have in this car... 700r4? thanks for any help.

brian

sofakingdom

iTrader: (1)

Sorry, no.

The only kind of rear that's a direct bolt-in to a 82-92 Camaro or Firebird, is one out of a 82-92 Camaro or Firebird.

The ones out of 93-02 Camaro and Firebird are almost a direct bolt-in, but not quite. They're the only other ones that can be put in without EXTENSIVE modification of something; either the car or the rear.

Yes your trans should be a 700. If it's a 6-cyl one, you won't be able to use it behind a V8. Won't bolt up.

naf

iTrader: (7)

Your second gen rear won't fit without major modifications. It relies on leaf springs for support. Your '89 uses coil springs with torque arm and panhard bar to locate the rear. Pretty much your only swap candidates are other third gens or the fourth gen rear (which is a hair wider). None are particularly noted for strength. The later 28 spline 10 bolts (started in '89 you may be lucky) are a little stronger and the Borg Warner 9 bolts are beefier. Nine bolts are rare and parts for them are hard to find and expensive. There's supposedly a Dana out there but it's extremely rare.

The ten bolt with an aftermarket posi and some reinforcements will probably do fine for your app. Next step up would be an aftermarket unit in the plus $1200 range.

89fbrestor

ok things for the info..... bummer i was going to get it for 150$ so would it be hard to changed the gears myself if i bought them. also what would be ideal for gears in this car/set up 350(350hp/75shot juice) 700r4 trans ? i'm not worried that much about gas, but i would like to drive it around and not wind it out..... gosh i sound like an idiot lol

naf

iTrader: (7)

The 700 R4 has a low first gear. On the street I'd go 3.23-3.42. Just my opinion mind you. Before you buy gears and go to the trouble of swapping them in you may consider swapping the entire rear for one that already has the ratio you want. Most V6's came with the better ratios and used rears can be had for around $150 or so. Compare cost and job difficulty.

I'd focus on the 28 spline axles vs. the earlier 26 spline and consider an aftermarket posi unit. Open yours up first, of course, to see what you have.

Good Luck.

89fbrestor

oh ya i did'nt even think of that lol lol see i told ya i was stupid at this stuff i just read that about the v6 rear to. thank you very much for the info. greatly appreciated.

brian
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oh one more question. would the v6 rear bolt right up? or would i have to do some modifying ?

naf

iTrader: (7)

Bolt right up. Disk to drum may need some pieces/parts, usually e-brake cables but you might can get them with the replacment rear. I wouldn't swap in the earlier iron rear disks (89 and earlier?) if that's an option. Not much of an upgrade.

Always open the case of any used rear you look at. The ratio for 10 bolts is stamped in gear count on the ring gears.

89fbrestor

naf thanks a ton. you've been a great help. i'm going to enjoy fixing this car up.

brian