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Old 06-09-2014, 11:08 PM
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7.5 or 8.5 rear end?

Im trying to figure out if my truck has a 7.5 rear end its a 94 gmc sierra 4.3 v6 im going to start swaping an ls1 and wanted to swap the rear end to a 8.5 and add some gears to it ( if mines a 7.5

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Old 06-10-2014, 06:11 AM
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S series truck or full size 1/2 ton? If it's a full size 1/2 ton then it's the 8.5 rear end. The 7.5 was not used in full size trucks.
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Old 06-10-2014, 10:11 AM
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Its a 2 door short bed
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Old 06-10-2014, 12:18 PM
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That doesn't tell me anything. Is it a full size 1/2 ton 1500 or is it a S15?
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Old 06-10-2014, 04:08 PM
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Sierra is a full size. The Sonoma was the S10 variant.. so it has an 8.5" unless it's got the F44 package and then it would actually be a 9.5" 14 bolt
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Old 06-11-2014, 06:52 AM
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Quote:
Originally Posted by matt167 View Post
Sierra is a full size. The Sonoma was the S10 variant.. so it has an 8.5" unless it's got the F44 package and then it would actually be a 9.5" 14 bolt
Yes sir, Sierra does signify full size GMT-400 truck. RPO F44 signifies the "heavy half" that gets the 14 bolt 9.5" Semi Floating rear end.
If this is a 2wd Sierra, F44 will trigger the upgrade to 6 lug wheels, same as teh 4wd. The only 14 bolt 9.5" SF with 5 lug wheels was the 1990-1993 454SS, axles of which, are impossible to find.

Does F44 automatically get rpo Mt1 4l80-E? I'm guessing yes?

thanks

peace
Hog
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Old 06-13-2014, 12:05 PM
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Thanks, so then should I go ahead and add gears to this rear end itself?
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Old 06-13-2014, 01:49 PM
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What gears are in it now? What do you want to do with it? What transmission will you be using? How tall will the rear tires be?
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Old 06-13-2014, 10:51 PM
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It has stock gears I was thinking 3.73 gears im putting an ls1 that comes with a 4l60e im trying to keep the engine stock at first but later im going to add heads and mild cam
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Old 06-14-2014, 05:40 AM
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Stock gears in a 4.3L is probably 3.73's as is. Best check your RPO codes to see

GM RPO Codes - Axle & Ratio Identification - Sierra Gear & Axle
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Old 06-14-2014, 07:26 AM
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I thought I had seen they where somthing like 3.41s or something around that, but also ita not a posi
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Old 06-14-2014, 08:02 AM
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You need to find out what you have before you make plans to change it.
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Old 06-14-2014, 01:34 PM
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If it's a 3.42, the code is GU6. There are a couple 3.73 codes but I don't know what ones go to the GMT400 trucks.
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Old 06-14-2014, 04:19 PM
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3.42 to 3.73 is not worth the effort..... likely a big tire on it and an OD, at least 4.11's would be a good start. May even want a 4.56 depending on tire size.
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Old 06-14-2014, 05:15 PM
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I wanted 4.10s but one of my friends mentioned the fact that It was my daily driver
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