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I have recently converted my rear drum brakes to rear disc and upgraded the front to dual piston calipers on my 89 S15 Jimmy 4.3L Auto 2wd. I used parts from a 2000 Bravada (4WD) for the rear & 2000 S10 2wd for the front. My car stops much better in all situations. I also added a G80 in the rear of my 7.625 rear end which required a new ring/gear set due to the carrier breaks. Motive gear makes a 3:08 thick gear set for the G80 carrier so I was able to keep the original gearing. I have a rear sway bar ready to install from a 2WD S10.
 

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Discussion Starter #22
Hi all, hard to believe I started this thread 3 years ago already, hopefully some of you are still around!

I've decided to go the "stock" route and find a 2WD, 54.5", GM 8.5/8.6 to rebuild. The truck will never see slicks so I don't feel I will ever outpower an 8.5 and need a ford 8.8. The reason I decided to do a swap at all is to upgrade to disc brakes and at the same time I'll replace the gov lock on the "new" rear.

I just want to clarify a few things I've read before I start trying to source a rear.

From what I've gathered, I'd be looking for an 8.6 (I've read the 8.5 only came with drums and the 8.6 only came with disc??) out of a 2000+ 2WD s10/blazer. Does that sound about right? Am I missing any important details?
 

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My guess is you’ll need to find one from a manual 2wd Blazer, or manual 2wd pickup. Not sure there was any rhyme or reason as to which one they were put in.
 

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Because that's the models GM put them in mostly. 4.3L V6 w/5speed.
 

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Discussion Starter #26
Because that's the models GM put them in mostly. 4.3L V6 w/5speed.
Ah I see that now, thanks.

From the list I'm looking at only 8.5s behind auto transmission were 2wd 1995-1997 s10.
Manuals had 8.5s in 2wd 96-03 s10 and 2wd 95-05 s10 blazer.
 

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Ah I see that now, thanks.

From the list I'm looking at only 8.5s behind auto transmission were 2wd 1995-1997 s10.
Manuals had 8.5s in 2wd 96-03 s10 and 2wd 95-05 s10 blazer.
I don't know of any autos that got them. I know mine didn't.
 
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Discussion Starter #29
Is concerning myself in ratios a moot point if I plan on replacing the gov loc? (It can easily be changed when upgrading?)

For the choices available with disc I would have the option between getting either:
00-03 s10 with 3.08 ratio
00-05 s10 blazer with 3.42 ratio

I know nothing and have done no research on ratios to know what would be best for my application. Any suggested threads where I can read up on the topic?
 

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time to get cereal
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There are online ratio calculators if you know what kind of highway RPMs you want to be turning. Higher numerically will make it get out of the hole sooner but the cruising RPMs will be higher. Depends on what you want. 3.08:1 is going to be more of a dog off the line than a 4.10:1
 

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You should also take into account the axle shafts will likely be worn at the outer bearing surface and need to be replaced. I found it not much more expensive to go with Moser axles. They claim they are 15% stronger, so it seemed worth the slight increase if I was having to replace the axles anyway.
 

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Discussion Starter #32
This is very helpful info I found on another forum from LsXblaze:

How to find S10 8.5" rear end

RPO codes:
GT4-3.73 gear ratio
GT5-4.10 gear ratio
GU4-3.08 gear ratio
GU6-3.42 gear ratio
G80- Positraction, Limited Slip
LB4- 4.3 V6 TBI
LN2- 2.2l 4cyl MFI
LU3- 4.3 V6
L35- 4.3 V6 CPI
M30- Auto 4 SPD trans
M50- Man 5 SPD trans


S10 Pickups
1995 s10 2wd 8.5 rear, (LB4,L35,M30,GU6)
1995-1997 s10 2wd 8.5 rear, (LN2,M30,GT5)
1996-1999 s10 2wd 8.5 rear, (L35,M50,GU4,G80)
2000-2002 s10 2wd 8.5 rear, (M50,GU4,G80)
2003 s10 2wd 8.5 rear, (LU3,M50,GU4,G80)

S10 Blazers
1995-1997 s10 blazer 2wd 8.5 rear, (L35,M50,GU6,G80)
1998-1999 s10 blazer 2wd 8.5 rear, (L35,M50,GU6,G80)
2000-2001 s10 blazer 2wd 8.5 rear, (L35,M50,GU6,G80)
2001-2004 s10 blazer 2wd 8.5 rear, (M50,GU6,G80)
2003-2005 s10 blazer 2wd 8.5 rear, (M50,GU6)

So... for example if you are looking for a 8.5 rear end with 3.42 gears and posi, you can find it in a v6 blazer 2wd with a manual 5spd trans...

There are also 8.5 rear ends in 4x4 s10's but i did not list them... Hope this helps find the rear end you want.
 

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That list is helpful, but don't read it as you will find 8.5s on those combos every time. Over the years I've learned it is necessary to visually confirm it is an 8.5 rather than any formula that is given for RPO, VIN, etc.

With that said, excluding ZR2, manual Blazers are where I've found all the 8.5s I've come across in both 2WD and 4WD flavors.
 

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Discussion Starter #35
That list is helpful, but read it as you will find 8.5s on those combos every time. Over the years I've learned it is necessary to visually confirm it is an 8.5 rather than any formula that is given for RPO, VIN, etc.

With that said, excluding ZR2, manual Blazers are where I've found all the 8.5s I've come across in both 2WD and 4WD flavors.
From what I've gathered the 1999+ 2WD blazer is going to be my only option, since I'm looking for disc brakes.
 

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You can always swap the disc components.
 

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Discussion Starter #37
You can always swap the disc components.
I've got a 7.5 in the truck now.
If I'm going to put the effort into a rear I'd rather do it to an 8.5, If I'm going to swap out the rear I want the discs to come with it.
That's my thought process at least.
 

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The brakes are the same. Find a cheap busted 7.5 with discs and do the swap. Or hold out.

BTW...your list isn't completely accurate.
 

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Discussion Starter #39
The brakes are the same. Find a cheap busted 7.5 with discs and do the swap. Or hold out.

BTW...your list isn't completely accurate.
It's tough to find good info. While I'm sure everyone is trying to help it causes a lot of confusion when they give information without being 100% sure it's accurate.

I wouldn't have a clue which 7.5s had disc to look for a busted one.
 

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Any late model Blazer with an automatic. If it doesn't have the bulge on the tubes, it's a 7.5. 2 or 4 door.
 
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