8.5 S10 rear

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8.5 S10 rear

Postby flea » Fri Oct 17, 2008 6:48 pm

I think I found an 8.5 rear.Its in a 97 S10 I was told had a 4.3 with a SIX speed transmission? Was hoping this would be the same width as my 87 S10 . The differences I noticed was the brake lines were different and it looked bigger than my 7.5..I went to look in the glovebox for RPO codes but the sticker isnt there.Does anybody have any idea what gears to expect ?Can you I.D a posi without opening the cover?Also he wants 250 fo it ?
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Re: 8.5 S10 rear

Postby s10studduts01s » Fri Oct 17, 2008 7:00 pm

if he is saying it came like that stock then he is lying and i wouldnt trust anything he says
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Re: 8.5 S10 rear

Postby screamen_seamen » Sun Oct 19, 2008 8:54 am

Starting in 1996 Every S10 with a Vortec 4.3 5speed had a 8.5" rear with the single horizantal shock on the right side. The only gear I know of them having is a 308, and the gears and limited slip that is in it is changable with a 88-98 full size 2wd with a 8.5" rear. A 4cyl or automatic truck will not have this rear.
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Re: 8.5 S10 rear

Postby jody » Sun Oct 19, 2008 9:12 am

Best thing to do is know what you are looking at to make sure its a 8.5 You know what a 8.5 looks like?If so, then never mind this......On the axel tubes, right befor they go into the pumkin(center section) they SWELL. It is like looking at night and day.You can tell...
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Re: 8.5 S10 rear

Postby Triaged71 » Sun Oct 19, 2008 12:59 pm

flea wrote:...Can you I.D a posi without opening the cover?Also he wants 250 fo it ?
1) It would not be an Eaton Posi™ unless it was swapped in. From the factory the optional diff is an Eaton Gov-Lock™.
2) You should NEVER buy a rear axle without AT LEAST pulling the diff cover and checking the condition, ID'ing the R&P ratio, and the differential type.
3) There are a bunch of people out there that (because of ignorance or lack of character) will try to sell you a 7.5/7.6 and tell you it is a 8.5.
4) AFAIK the only ratio that came in 2wd 8.5s was 3.42.
5) Listen to Jody about ID'ing the 8.5

Here is a picture of my 2000 Blazer 8.5" (which didn't have the 3rd shock FWIW)
Image
'87 S10 ext-cab w/ 12" B-body front brakes, 8.5" rear axle with disc brakes, and still powered by a mighty 2.8L V6
'71 K5 Blazer with 1-ton axles, 4.56 gears, 37" Nittos, and powered by a 400SB
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Re: 8.5 S10 rear

Postby flea » Sun Oct 19, 2008 3:28 pm

I went today with a tape measure and there is no way that rearend is an 8.5.The pumkin is the same as a 7.5 that 8.5 pic is totally different the reason I thought it may have been an 8.5 was on the back of the drum there are 4 bolts I guess that hold the axles in and on mine there is one at the top and bottom thanks every body..This guy was looking for a sucker and almost had one ..
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Re: 8.5 S10 rear

Postby Triaged71 » Sun Oct 19, 2008 3:54 pm

That would make it a 7.6" axle. The R&P is actually the same as the 7.5" but it uses 28-spline axles rather than 26-spline. People tried to pass them off on me as 8.5" 3 times before I finally found my 8.5". Buyer beware! Glad you didn't get taken.
'87 S10 ext-cab w/ 12" B-body front brakes, 8.5" rear axle with disc brakes, and still powered by a mighty 2.8L V6
'71 K5 Blazer with 1-ton axles, 4.56 gears, 37" Nittos, and powered by a 400SB
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Re: 8.5 S10 rear

Postby monzaz » Mon Oct 20, 2008 6:52 am

Most of those 8.5 10 bolt 2wd axles came with 3.08...this is because they came with the 4.3 and 5 speed option. 3.42 would have been a special order for a tow package...probably.

Eihter way you'll probably have to upgrade the posi and the gear ratio if you really want to have some fun with it. BUT the difference in strength from a 7.5 or 7.6 is HUGE! The 8.5 rear use al lthe same pinion bearings as the 12 bolt muscle car chevy rear. Carrier bearing are still the 10 bolt size but in the 1999 and up they changed the carrier bearigs in the 1/2 ton trucks to a36 bearing set which is the same as 12 bolt chevy again.

I do not know if this change was passed onto the later model s-10 8.5 2wd or zr2 rear.

it would have been real cool if they used the same 1/2 ton zr2 axle bearing in the 2wd ...But I will still take this 8.5 2wd over most rears. definetely of the 9" stock ford rear anyday.
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Re: 8.5 S10 rear

Postby Triaged71 » Mon Oct 20, 2008 10:41 am

Because you had to get the high output 4.3L (not just the normal 4.3L) and a stick, the 8.5 only came with specially optioned trucks. I don't remember where I read it but the only ratio for 2wd is supposed to be 3.42, normal 4x4 3.42, and ZR2 3.73. When I got mine they had 2 8.5s and both of them had 3.42 gears...so all the S10 8.5s that I have ever seen were 3.42 :lol: If you go to http://www.car-part.com they list the options below for a 2000 blazer:

4x2, 7-5/8" ring gear, 3.08 ratio (opt GU4)
4x2, 7-5/8" ring gear, 3.42 ratio (opt GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear; 3.08 ratio (opt GU4)
4x2, 8-1/2" ring gear (3.42 ratio, GU6)
4x4, w/ZR2 opt (3.73 ratio GT4)
4x4, w/o ZR2 opt; 8-1/2" ring gear (3.42 ratio, GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear; 3.42 ratio (opt GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear; 3.73 ratio (opt GT4)


One of these days I'll pull the carrier out of mine and find out which bearings it has. I have wondered this for a while as well. Did they use up all the old 8.5s in the S10s or did they switch them over first? My 2000 being near the change over year could be either way. I don't know if there is a way to tell them apart from the outside. I wish GM put a Posi™ diff in trucks :( Mine has a Gov-Lock™ and one of these years it will have to go in favor of something that doesn't suck.
'87 S10 ext-cab w/ 12" B-body front brakes, 8.5" rear axle with disc brakes, and still powered by a mighty 2.8L V6
'71 K5 Blazer with 1-ton axles, 4.56 gears, 37" Nittos, and powered by a 400SB
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Re: 8.5 S10 rear

Postby flea » Mon Oct 20, 2008 2:35 pm

Another question I have a friend that said he was going to give me his old rearend out of a 94 S10 7.5 28 spline limited slip could I swap the 28 spline axles and carrier in my older 26 spline 7.5 So I wouldnt have to drop the entire rearend? :?
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Re: 8.5 S10 rear

Postby Rickracer » Mon Oct 20, 2008 2:53 pm

It's quicker, safer and less messy to swap out the whole thing, unless you know how to set up gears. :wink: 8)
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Re: 8.5 S10 rear

Postby s10studduts01s » Mon Oct 20, 2008 2:55 pm

Its possible but you'd be better off to just swap the rear end cause you'll need different bearings i do believe. As well as change out the gaskets
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Re: 8.5 S10 rear

Postby flea » Mon Oct 20, 2008 8:16 pm

well looks like I will swap rearends then.. Have no idea how to set up rears..Thanks again
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Re: 8.5 S10 rear

Postby SNK SKNR » Mon Oct 27, 2008 11:14 am

screamen_seamen wrote:Starting in 1996 Every S10 with a Vortec 4.3 5speed had a 8.5" rear with the single horizantal shock on the right side. The only gear I know of them having is a 308, and the gears and limited slip that is in it is changable with a 88-98 full size 2wd with a 8.5" rear. A 4cyl or automatic truck will not have this rear.



Wanna bet? :mrgreen: I have a 1997 GMC Sonoma with the 4.3 and a 5 speed with the single shock (also called the "hop shock", its part of the ZQ8 suspension package)...and mine most definitely has the 7.625 rear...I swapped in a zexel and did the gears on it, so I know for a fact....It's coming out now anyways....I got an actual 8.5 ready to go in (took a LONG time to find one). 8)
'97 Sonoma ZQ8, 4.3, 5-speed
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Re: 8.5 S10 rear

Postby monzaz » Tue Oct 28, 2008 7:56 pm

Well that 3.42 being the only option is wrong then I have one right now on the rack with 3.08 and a gov lock posi. I will try and get the numbers off the tube and see if some one was in there.
Maybe a standard option is 3.42 But I am sure again you can option what ever ratio you really want as long as your paying for it? Right? LOL. Jim

If it is one thing I have learned about cars diffs and all cars for that matter IS YOU NEVER know what options can be in a car/truck. Anything goes and does. Combos that should not be can be by mistake.
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Re: 8.5 S10 rear

Postby 1quikz » Mon Jan 19, 2009 12:16 pm

Triaged71 wrote:Because you had to get the high output 4.3L (not just the normal 4.3L) and a stick, the 8.5 only came with specially optioned trucks. I don't remember where I read it but the only ratio for 2wd is supposed to be 3.42, normal 4x4 3.42, and ZR2 3.73. When I got mine they had 2 8.5s and both of them had 3.42 gears...so all the S10 8.5s that I have ever seen were 3.42 :lol: If you go to http://www.car-part.com they list the options below for a 2000 blazer:

4x2, 7-5/8" ring gear, 3.08 ratio (opt GU4)
4x2, 7-5/8" ring gear, 3.42 ratio (opt GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear; 3.08 ratio (opt GU4)
4x2, 8-1/2" ring gear (3.42 ratio, GU6)
4x4, w/ZR2 opt (3.73 ratio GT4)
4x4, w/o ZR2 opt; 8-1/2" ring gear (3.42 ratio, GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear; 3.42 ratio (opt GU6)
4x4, w/o ZR2 opt; 7-5/8" ring gear; 3.73 ratio (opt GT4)


One of these days I'll pull the carrier out of mine and find out which bearings it has. I have wondered this for a while as well. Did they use up all the old 8.5s in the S10s or did they switch them over first? My 2000 being near the change over year could be either way. I don't know if there is a way to tell them apart from the outside. I wish GM put a Posi™ diff in trucks :( Mine has a Gov-Lock™ and one of these years it will have to go in favor of something that doesn't suck.



Car-part search results for a 2000 s10

4x2, 8-1/2" ring gear (3.08 ratio, opt GU4)
4x2, 7-5/8" ring gear, w/chassis pkg ZQ8, 3.08 ratio (opt GU4)
4x2, 7-5/8" ring gear, w/chassis pkg ZQ8, 3.42 ratio (opt GU6)
4x2, 7-5/8" ring gear, w/chassis pkg ZQ8, 3.73 ratio (opt GT4)
4x2, 7-5/8" ring gear, w/chassis pkg ZQ8, 4.10 ratio (opt GT5)
4x4, 8-1/2" ring gear, w/"ZR2" opt (opt 3.73 ratio)
4x4, 8-1/2" ring gear, w/o "ZR2" opt; (3.42 ratio, opt GU6)
4x4, 7-5/8" ring gear, 3.08 ratio (opt GU4)
4x4, 7-5/8" ring gear, 3.42 ratio (opt GU6)
4x4, 7-5/8" ring gear, 3.73 ratio (opt GT4)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/o 3rd shock; 3.08 ratio (opt GU4)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/o 3rd shock; 3.42 ratio (opt GU6)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/o 3rd shock; 3.73 ratio (opt GT4)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/o 3rd shock; 4.10 ratio (opt GT5)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/3rd shock; 3.08 ratio (opt GU4)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/3rd shock; 3.42 ratio (opt GU6)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/3rd shock; 3.73 ratio (opt GT4)
4x2, 7-5/8" ring gear, w/o chassis pkg ZQ8; w/3rd shock; 4.10 ratio (opt GT5)
1997 S10- RCSS, 2000 zq8 Clip and interior, Lowered 2/3, Blazer Front Brakes, 350 vortec w/LT1 cam, rebuilt 4l60e and 3.73 Zexel Torsen 10 bolt.
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Re: 8.5 S10 rear

Postby Triaged71 » Mon Jan 19, 2009 2:14 pm

1quikz wrote:...Car-part search results for a 2000 s10...
Thanks for posting that up. Guess I got stuck on Blazers and forgot the pick-ups :oops:
'87 S10 ext-cab w/ 12" B-body front brakes, 8.5" rear axle with disc brakes, and still powered by a mighty 2.8L V6
'71 K5 Blazer with 1-ton axles, 4.56 gears, 37" Nittos, and powered by a 400SB
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Re: 8.5 S10 rear

Postby 6SpeedBlazer » Thu Jan 22, 2009 2:19 pm

screamen_seamen wrote:Starting in 1996 Every S10 with a Vortec 4.3 5speed had a 8.5" rear with the single horizantal shock on the right side. The only gear I know of them having is a 308, and the gears and limited slip that is in it is changable with a 88-98 full size 2wd with a 8.5" rear. A 4cyl or automatic truck will not have this rear.


FAIL!

starting in 1995 for the L35 high output 4.3/M5 combo it was an OPTION. then starting in 98/99 it was standard.

3.08 and a gov-loc is the standard gear ratio for a 4.3/5speed truck. but they had the option of getting 3.42's

3.42 and a gov-loc is the standard ratio for a 4.3/m5 blazer.

zr2 pickups and blazers all got the 8.5 with 3.73 gears and a gov-loc

also there are two different 8.5 rear ends, kinda like the 7.5

there is the standard 8.5 then around 2000 they updated the carrier bearings, making them larger. gm refers to this as the 8.625 rear end for whatever reason
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Re: 8.5 S10 rear

Postby purevil115 » Fri Jan 23, 2009 4:41 pm

I got a 8.5 out of a blazer thats a 2001 and it has the code gu6 in it which is 3.42 but it doesnt have a g80 in it. whats that mean, did someone replace the locker with an open rear end or something.
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Re: 8.5 S10 rear

Postby Triaged71 » Fri Jan 23, 2009 4:52 pm

Did you pop the diff cover off to ID the diff, spin one wheel and the other one went backwards, or go by glove box RPO codes?
'87 S10 ext-cab w/ 12" B-body front brakes, 8.5" rear axle with disc brakes, and still powered by a mighty 2.8L V6
'71 K5 Blazer with 1-ton axles, 4.56 gears, 37" Nittos, and powered by a 400SB
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