I have an 86 IROC-Z and need to know what size the rear is...is it a 10-bolt...8.5 inch?

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1986 Metallic Blue IROC-Z
80k miles, 305 TPI
Mods:
-Edelbrock Hi-Flow baseplate
-Dynomax Cat-back
-gutted MAF
-K&N's
-airfoil
-shiftkit

 

Commonly called the 7.5", yours should actually be a 7 5/8". 86 was the changeover year to the larger ring gear. Both are interchangable.

The 8.5" 10 bolt was never offered in a third gen unless you have a metal plug in the rear cover. Then it's a Dana44 which is a 8.5" but I really doubt you have that.

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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.447 altitude corrected to 10.99
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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Could be a 9 bolt too. The first year for Iroc 9 bolts was either 86 or 87.

Miles

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88 427 Big Block Camaro
(Best 1/4) 12.18 @ 113mph 1.75 60ft
(Best 1/8) 7.76 @ 94mph 1.72 60ft

Currently installing 3.73's into my 9 bolt (YES, it is a 9 bolt & YES they are 3.73's, not 3.70. I currently have 4.10 gear sets and new series 3 posi carriers for sale for 9 bolts )
www.koolmeister.com

 

I have the 2.73 posi rear right now with the 7.5inch...and want to upgrade to 3.42's. Found richmond gears on the summitracing site and they are for:
GM: 10-bolt, 7 1/2 in., 7.625 in., 3.42 ratio, 2 series: carrier, ring and pinion

WOuld these work? and do i need an installation kit?

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1986 Metallic Blue IROC-Z
80k miles, 305 TPI
Mods:
-Edelbrock Hi-Flow baseplate
-Dynomax Cat-back
-gutted MAF
-K&N's
-airfoil
-shiftkit

 

Yes, those are it. If you are installing the gears yourself, I'd get the kit. If somebody else is doing (somebody who does rears professionally I hope) then they should already have shims and such, so I wouldn't bother.

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1987 Trans Am 305
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