89' Formula LB9/MM5/G80/N10/GM3....ONLY 42....

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Apr 30, 2013 | 04:54 PM

#101

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From: Carson, CA

Car: '88 GTA, 90 Formula

Engine: 5.7 TPI, fed growth hormones

Transmission: 700r4 4u2?

Axle/Gears: 9bolt

Re: 89' Formula LB9/MM5/G80/N10/GM3....ONLY 42....

Quote:

Originally Posted by timfitz63

Here are a couple sites that help to decode the RPO's:

http://www.c2e.info/rpocodes/
http://www.lesabret-type.com/GMRPOCodes.html

G80 = AXLE, POSITRACTION, LIMITED SLIP
GM3 = AXLE REAR, 3.45 RATIO

If you don't have the 3.45 differential ratio, you've probably got something close to that (like 3.42 = GU6, for example). I don't know if other ratios were available on the '90 Formulas; I thought all the Third-Gen LB9/N10/MM5 cars got a 3.45 ratio...?

You are right on the money. In '90 they went to the (weaker) 10-bolt Chevy rear end, so thus it is GU6/3.42 ratio, because the B/W Australian 9 bolt was no longer available. So for whatever it's worth, I do have a 5-speed Formula with all the "sleeper" options plus T-tops.

TA

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89' Formula LB9/MM5/G80/N10/GM3....ONLY 42....-90formula.jpg

May 1, 2013 | 07:54 AM

#102

okfoz

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From: Doghouse ······································ Car: 1989 Formula 350 Vert Engine: 350 L98 Transmission: 700R4 Axle/Gears: B&W 3.27

Car: 87 Formula T-Top, 87 Formula HT

Engine: 5.1L TPI, 5.0L TPI

Transmission: 700R4, M5

Axle/Gears: Sag 3.73, B&W 3.45

Re: 89' Formula LB9/MM5/G80/N10/GM3....ONLY 42....

Starting in 1990, the Borg & Warner (9 Bolt) axle was dropped (some axles remained in stock and some cars have been found to have them for 1990, but there was no RPO on the SPID for it.) Therefore for 1990 - 1992 the SPID RPO would be GU6 which is the Saginaw 7.625 "10 Bolt" axle that has the 3.42 gear instead of 3.45

So US Formulas with the LB9/MM5:
1987 - 1989 - GM3 (3.45) Borg & Warner (9 Bolt) axle
1990 - 1992 - GU6 (3.42) Saginaw (10 Bolt) axle

This was standard fare for the Formula, I have never seen a US Formula with the LB9/MM5 without a GM3 or GU6, if you don't have it and the car was not an export I would be more than interested

Hope that helps.

John