Could someone tell me what gears were put in a 89 formula 350, or better yet tell me how to find out. Any help is appriciated

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89 Formula
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Crawl under the car and look on the front of the right (passenger side) axle tube. There will be a three-character code stamped on the tube. You may have to brush dirt/oil/rust off to read it.

Look up the code in a manual - my Haynes has the codes in it. It will tell you if standard (open) or posi, and the gear ratio that came in the axle from the factory.

To really know what is IN the axle now, you need to take the cover off and either count the teeth on the pinion and ring gears, or look for the number stamped on them. Divide the larger by the smaller for the ratio. Both numbers are usually stamped on the end of the pinion.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
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89 350's are really easy to figure out, as they only had two gears available. If you have a single cat, then you have a 9-bolt posi 2.77 rear end. If you have dual cats, you have a 9-bolt posi 3.27 rear end.

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Guess I should have read through my haynes book a bit more. I cleaned my axle off but there is no sign of any code anywere. I guess that the person who had my car before me replaced that part. I'll find out when i go to the shop. THANKS for the help though.

Thanks kev, thats some good info to know. Much appreciated Guys.

Kevin, thats not true. My 89 350 GTA came factory with a 9 bolt 3.27 posi with a single cat. I know so because i checked the option sticker in my console. Not arguing, just clarifying.

Dammit, I swear... every little trick of mine keeps going down the tubes. GM is crazy!! The G92 option package in 89-92 is supposed to mean the better rear gears, oil cooler, dual cats, and the better cam in the 305's. Now you say you have a G92 car with a single cat? *sigh* I cant win.

In 1989, the dual cat was a specific option IRRC. In 1990 your G92 trick works. In 1991, its different again as you got dual cats based on engine (350) or G92 (305s).

AND THEN, GM created combos that were NEVER suppose to exist at all. I am not sure how many were made, but I got some odd-ball aluminum drum rear brake with my 1991 L98 GTA. Oh well, at least I can put 15" rims on my car for my snowies. (Yes, my car DID come stock with 245/50/16s cross-laced rims).

To know what your car originally came with, look at the SPID label in the center console. If you think they have been changed, count the teeth on the ring gear and pinion, and divide the ring gear by the pinion.

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or he could simply read the tag bolted thru one of his 9-bolts on his rearend

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89 FORMULA 350,WS6 SUSPENSION,FRESH 355 MOTOR,TCI 12" STREETFIGHTER,TRANSGO SHIFT KIT,3.70 GEARS,SLP REAR CONTROL ARMS/PANHARD,HOTCHKIS STB,FORMULA GP'S,FLOWMASTER EXHAUAST,58 MM BBK,MINIRAM INTAKE,ALL FREE MODS(HEADERS WAITING IN GARAGE)SLP 3/4",NO CATS,

My single cat. 89 formula came with 3.27 posi as well.

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87 IROC, 350/5 speed.
89 formula, L98.

Thanks guys, my mechanic told me i had 3.27's. I've been told that i need an all new rear housing if i wanna get 3.73's. Is this true? He also told me for what i've done with my car so far this should probably be the next step to take.

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89 Formula
Edelbrock Headers+
Catback system,Torque Converter,Rebuilt Trans,B&M Megashifter, K+N air filter, Accel Distr. Module, MSD coil,New Fuel injectors with adj. regulator, ECM with performance prom,and a Crate ZZ3 350

I don't think that is correct. If I'm not mistaken, as long as you have a 3.07 or up gear & carrier (housing) you don't need a new one.

If you have the 9-bolt rear end, which you should, you cant get 3.73's, as they are for 10-bolt rear ends. You need 3.70 gears, which I know of two places. Randy's Ring&Pinion, and Drive Train Specialists. Hang onto your wallet, as they're expensive.

Would it be cheaper to put a ten bolt in place of the nine. Can it be done if so?

Drewcifur,

Yes it can be done. That is what I did to mine, and it was a whole lot cheaper.

Sparks a flyin'.

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