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Discussion Starter #1 (Edited)
I noticed from the gasket I have a 7.5" pumpkin. It's a 3.42 posi.
I'm wondering if the 3.72 gear/housings are the 8.5" ? Anybody have
any info of the different sizes of the rear axles compared to gear
ratio ? I'm looking for a nice 3.72 and I'd like it to be with the 8.5
housing..No particualr reason..Any info thanks.

In the meantime, I'll try a search to try and get a handle on this.
With 117,000 on it the gears, inside looked almost brand new
and the 85/90 was barely discolored..I like Valvoline gear oil. I
change the gear oil every 25,000. It sure has remained strong.
 

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Poor-ass college student
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Nah, mine has an 8.5" rear. It is only in 4.3L with manual tranny, maybe only extended cab anf the other stuff??
 

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Discussion Starter #4
Thanks. As posted above there's 8.5's for the s-trucks. I'll look at
the 2whe Jimmys and Blzr's. Maybe taht's where they're at. I have a
gasket for an 8.5 sitting in the shed. Now to find a 8.5-3.72 posi....
:evilg:
 

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the only 2wd S10's that got an 8.5 were all 2000 and up V6 5 spd trucks and the only gear ratio available from the factory was a 3.08
on pre 2000 trucks you could get a 2wd 8.5 if you were lucky enough to find a HO V6 (L35 or vin W) that had a 5spd behind it (more likely to find that setup in a sonoma than an S10)

also all ZR2's had 8.5's and thos usually came with 3.73's but were ZR2's so they were alot wider than a standard 2wd rear

good luck finding an 8.5 rear in a junk yard I have been looking for years now and cant find one
and even if you do plan on paying a pretty penny for one
thjey are running about 6-900 bux around here
 

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Discussion Starter #6
Thanks for the heads-up. I have a num of pick a part yards around
me, and I'm pretty sure not too many people know of the 8.5-3.72
gear assy. There's always a few Blazr's an Jimmys around these
yards so I'll take a look. Here's something I hope may help you.
I was able to get a 2001 zq-8 steer box for my ole Slonoma
for 75.00 bucks + tax. Box was like new. I've a few other items
through this site. Maybe there's something close to you..Link>

www.car-parts.com
 

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footbraker
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Biggun said:
Nah, mine has an 8.5" rear. It is only in 4.3L with manual tranny, maybe only extended cab anf the other stuff??
Never seen one, must be rare. Maybe it's special order?
 

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Gaaoooooo
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Rhansen said:
Never seen one, must be rare. Maybe it's special order?
Rare possibly, I have an 8.5 posi with 3.08's, 2000 4.3 5spd, my brother has one as well, 2000 xtreme 4.3 5spd. I suppose it could be considered special order since I believe when you ordered the zq8 or xtreme package with a 4.3, atleast online, it would default you to the 4L60-E which would come with a 7.5/7.625 rear.
 

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Never Finished
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so you guys are saying that I should have the 8.5" rear end? Is there an RPO code to tell, or would I have to measure the ring gear to be sure?
 

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well do you have an 8.5
yes I will guarantee that you do if you have a 2003 with a 4.3 and a 5 spd because thats all that was available with that engine tranny combo and you also have 3.08 gears and a locking rear diff
also because thast all that was available with that engine tranny combo
(all of this only applies to 2000 and later trucks)

and yes there is an RPO code that will tell you this but I dunno what the 8.5" rear code is but the 3.08 and locker codes are
GU4 (3.08 gears)
and
G80 (locking rear differential)
 
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