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Independent
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That's to funny, I did some searching on my own and came up with that one too. Just thought I would see what someone who actually new about this would say. I'll check into getting that one. Thanks.
 

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Cant find the numbers to tell if I have 8.5 or 75/8 how to tell?
I know I have GU4 gears (glove box and forums thanks)...but how o tell?
95 xcab reg box 4.3 5 speed man....122.9wheelbase ...


Thanks
 

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FWD's suck
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1,745 Posts
Discussion Starter · #223 ·
to start the covers look diffrent. a 8.5 cover is completly round almost a perfect circle. A 7.5 cover isnt the same and has more of a square look. If my memory serves me right i dont think many, if any s10's came with 8.5's until 98ish. My 94 4.3 5 speed has a 7.5
 

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i have a 2003 s10 4.3l auto. i was wondering if i got a 10 bolt eaton posi 28 spine. if it would work since i have a one spin wonder rear end lol? if it will can u tell me what else i need to get it to work just fine i dont plan on putting alot of hp to it just maybe 400 to 500. any comments would b great
 

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Gears and Differentials
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If you have the 7.5 (7.62) rear end then 400 to 500 HP will likely break it. If you have the 8.5 rear end then it will be 30 spline and will handle that amount of power.

If you have the 7.5 and a 3.23 to 4.10 gear then the Eaton will work. If you have a 3.08 to 2.41 gear then the Eaton will not work because the Eaton is only available in a 3 series. You will need bearings ahd shims to install it. http://www.nastyz28.com/forum/showthread.php?t=19773&highlight=install+posi
 

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Wow, this thread delivers! Thanks to everyone who has contributed. I've been repairing gearboxes in machinery for years and finally decided to break down and do my rear, and I realised I know nothing about them (until I read this thread).
I always knew I had an 8.5" rear (OEM in my '93 2WD 4.3), but never knew what gears I had. Now I know it's a 3.08. All I have to do now is save up a little bit of $$ and jump in.
 

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im in the process of lifting my s10 i have a 2003 ext cab 4x4 4.3 that im putting 33"s on i curently have 4.10 gears with 7.5 rear and want to switch out to 3.73 in an 8.5 is this a smart choice
 

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FWD's suck
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1,745 Posts
Discussion Starter · #228 ·
im in the process of lifting my s10 i have a 2003 ext cab 4x4 4.3 that im putting 33"s on i curently have 4.10 gears with 7.5 rear and want to switch out to 3.73 in an 8.5 is this a smart choice
If you switch the rear to a 8.5 with 3.73's then you will have to change the front gears to 3.73's also. You would be better off though changing the gears in the 8.5 to 4.10's. The bigger the tire you run is like running a smaller gear.
 

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FWD's suck
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1,745 Posts
Discussion Starter · #229 ·
Wow, this thread delivers! Thanks to everyone who has contributed. I've been repairing gearboxes in machinery for years and finally decided to break down and do my rear, and I realised I know nothing about them (until I read this thread).
I always knew I had an 8.5" rear (OEM in my '93 2WD 4.3), but never knew what gears I had. Now I know it's a 3.08. All I have to do now is save up a little bit of $$ and jump in.
You may want to check again. I dont know of any older s10's or blazers coming with the 8.5's until 98-99ish. Most of the ones that did come with the 8.5's were ZR2's or 5 speed trucks.
 

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Independent
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4,136 Posts
I got the book and dvd for christmas and the info and instructions are pretty good so anyone could follow them. I would recommend it, lots of good info and covers more than 1 type of rear. The one thing it didn't cover was the gm 10 bolt 7.5 with the gm gov lock. It did have the 12 bolt with the posi though so I think I can figure it out, I'll just watch a couple more times to make sure.
On a side note, I had a 91 Sonoma Reg cab, long box that I just sold had the 4.3 and the 5 speed and it had the 8.5 rear in it.
 

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Independent
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4,136 Posts
I have a question on dismantling the 7.5 with a G80 in it. How do you get the gov lock mechanism out so you can tear it apart, the book and dvd I got doesn't cover the g80 in a 10 bolt but covers the 12 bolt and they are totally different.
 

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Gears and Differentials
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1,395 Posts

You have to use this to disassemble the Governor Lock. Cost about $130 around 10 years ago.
 

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Gears and Differentials
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Yea, the parts for the Gov Lock are pretty expensive. The last governor that I bought was $75, and that was several years ago. If this is a street truck then the Eaton Posi or Torsen will work great. If it's for off road then look into a locker of some kind.
 

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BumblBXtreme
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177 Posts
ok guys i read this entire thread and im still wondering what rear end i got. i know i have 3.08 ratio (GU4) but i am still wondering if it is a 7 5/8 or a 8 1/2.... My dad teaches automotives at NAIT and he is trying to convince me that its the 7 5/8. My truck is a 2003 S10 Extreme 4.3 5 speed manual w/overdrive. it has drum brakes in the back btw. Any info into what you guys think it has would be great cuz i am in the process of deciding what is all needed to drop a 350 i got in. Thanks!
 

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Independent
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Post a pic, that is definative. Chances are 7 5/8. Very few came with the larger rear, usually only on long box with v6 and 5 speed.
 
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