Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
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Junior Member
Joined: Sep 2011
Posts: 6
Likes: 0
From: Oregon
Car: 86 Iroc-Z28 Camaro
Engine: 383 SB
Transmission: TH350
Axle/Gears: Stock disc brake 3.43
Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
I am swapping out my drum rear-end for a disc rear-end out of a 89 Irocz (or may just be a regular Z) parts car... Do they all have the same 3.42 gears and are they posi?
"Sorry for the dumb questions just trying to get my feet wet before I jump in the pool" Thanks guys
"Sorry for the dumb questions just trying to get my feet wet before I jump in the pool" Thanks guys
Joined: Jun 2000
Posts: 5,364
Likes: 51
From: Enschede, Netherlands
Car: 82 TA 87 IZ L98 88 IZ LB9 88 IZ L98
Engine: 5.7TBI 5,7TPI 5.0TPI, 5,7TPI
Transmission: T5, 700R4, T5, 700R4
Axle/Gears: 3.08, 3.27, 3.45, 3.27
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
no, 9 bolts and 10 bolts, different ratios available.
Joined: Dec 2005
Posts: 6,499
Likes: 31
From: Macon, GA
Car: 1992 Camaro RS
Engine: Vortec headed 355, xe262
Transmission: T56
Axle/Gears: 9-bolt 3.70
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
Disc or drum has no bearing whatsoever on what gear ratio it has.
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Joined: Feb 2009
Posts: 323
Likes: 3
From: Nowthen, MN
Car: 87 monte aerocoupe
Engine: 383 HSR w/ novi 2000
Transmission: Built 4l80e circle d converter
Axle/Gears: Currie 9" 3.89 gears
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
nope, you could have a disc rear with any ratio available in that given year. My 83 had a factory disc rear with 3.23's in it.
Thread Starter
Junior Member
Joined: Sep 2011
Posts: 6
Likes: 0
From: Oregon
Car: 86 Iroc-Z28 Camaro
Engine: 383 SB
Transmission: TH350
Axle/Gears: Stock disc brake 3.43
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
How did you guys find your gear ratio? Also, My fab mechanic mentioned a limited slip posi the other day? now he is kinda an older guy who has been through many years of logging but the man is a race-car builder! A DAMN GOOD ONE! but is there such a thing as "limited slip Posi?" (and yes I know drum vs. disc makes no difference on gear ratio!)
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iTrader: (5)
Joined: Mar 2011
Posts: 2,893
Likes: 4
From: Central Texas
Car: GTA
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: Aussie 9-bolt/3.27 posi
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
Jack up the rear end off the ground & support it by jackstands.
Put the tranny in Neutral & from under the rear of the car, rotate a tire by hand & watch the pinion/driveshaft rotate.
Count the pinion/driveshaft rotations for 1 tire revolution & you'll get your gear ratio.
For a 10-bolt:
If the pinion/driveshaft rotates 3 times for 1 tire revolution? You have a 3.08.
If the pinion/driveshaft rotates almost 3 times for 1 tire revolution? You have a 2.73.
If the pinion/driveshaft rotates almost 3 1/2 times for 1 tire revolution? You have a 3.42.
For a 9-bolt:
If the pinion/driveshaft rotates almost 3 1/4 times for 1 tire revolution? You have a 3.27.
Those are not the only ratios out there, but also are some of the most common that you'll find. Your IROC might have the 9-bolt/3.27 or 10-bolt/3.42, but after all these years, no telling if a previous owner has swapped it out after all these years. My daughter has a 1990 RS with a 1984 10-bolt/3.73 posi with aluminum drum brakes, all factory stuff from 1984 Z28 that I put in her car.
Put the tranny in Neutral & from under the rear of the car, rotate a tire by hand & watch the pinion/driveshaft rotate.
Count the pinion/driveshaft rotations for 1 tire revolution & you'll get your gear ratio.
For a 10-bolt:
If the pinion/driveshaft rotates 3 times for 1 tire revolution? You have a 3.08.
If the pinion/driveshaft rotates almost 3 times for 1 tire revolution? You have a 2.73.
If the pinion/driveshaft rotates almost 3 1/2 times for 1 tire revolution? You have a 3.42.
For a 9-bolt:
If the pinion/driveshaft rotates almost 3 1/4 times for 1 tire revolution? You have a 3.27.
Those are not the only ratios out there, but also are some of the most common that you'll find. Your IROC might have the 9-bolt/3.27 or 10-bolt/3.42, but after all these years, no telling if a previous owner has swapped it out after all these years. My daughter has a 1990 RS with a 1984 10-bolt/3.73 posi with aluminum drum brakes, all factory stuff from 1984 Z28 that I put in her car.
Joined: Dec 2001
Posts: 9,937
Likes: 636
From: Chicagoland
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
My '83 has a 10 bolt posi with 2.93 gears. My '89 has a 9 bolt posi with 3.45 gears. Both are disc brakes.
Joined: Aug 1999
Posts: 19,282
Likes: 103
From: Lawrence, KS
Car: Met. Silver 85 IROC/Sold
Engine: 350 HO Deluxe (350ci/330hp)
Transmission: T-5 (Non-WC)
Axle/Gears: Limited Slip 3.23's
Re: Are All 3rd Gen Disc Rear-Ends Posi 3.42's?
https://www.thirdgen.org/forums/tran...-10-bolts.html
Limited slip = posi
JamesC
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