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  #16 (permalink)  
Old 03-19-2010, 06:23 PM
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GM used the Eaton Posi in the truck 12 bolt in the late '60s and early '70s, but it wasn't very strong. The case would crack. Eaton has redesigned the case for the truck 12 bolt and now it is very strong. I can recommend the new Eaton Posi for the truck 12 bolt very strongly. There are also several other differentials that are good. The Truetrac works pretty well. I like it more for auto cross. The Lock Right will fit into the differential case that you have now without having to set the backlash again, but it can make some noise sometimes and jerk a little. The Detroit Locker is very strong, but expensive and has the same problems as the Lock Right. You don't want to use the old Governor Lock. It's weak. I also do not like the Auburn for several reasons.

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  #17 (permalink)  
Old 03-19-2010, 08:43 PM
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OK well then an eaton will suffice for when the time is right, for that matter my 12 bolt as it is will do the current job. What I will do is have it looked at for preload and contact pattern etc, the 3.73 is right for me/it. What had me going here was the thinking that I am wasting my $$$ on the truck 12 blt, that eaton will cost me no doubt, I have had this little c-10 for 23 years all along thinking I had a better 12 bolt than most... car guys get me every time lol
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  #18 (permalink)  
Old 03-19-2010, 09:37 PM
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Quote:
Originally Posted by Custom10
I have had this little c-10 for 23 years all along thinking I had a better 12 bolt than most... car guys get me every time lol
Well, you DO have it all over the car guys that have F-bodies and G-bodies that are saddled w/the pathetic 7.5"/7.625" diffs!! Those ARE bad.
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Old 03-20-2010, 09:45 AM
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how can i tell if its a truck 12 bolt?
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  #20 (permalink)  
Old 03-20-2010, 07:01 PM
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The car 12 bolt has a cover that is almost round. The truck 12 bolt cover is a little more flat on the left side and oval shaped on the right side.
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Old 03-20-2010, 09:23 PM
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isnt the truck 10 bolt a little wider? i opened the rear end up. im trying to find numbers to identify it. the caps holding the carrier in said gm 8703 276 n. does this mean anything?
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Old 03-20-2010, 09:29 PM
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Quote:
Originally Posted by dman0712
isnt the truck 10 bolt a little wider? i opened the rear end up. im trying to find numbers to identify it. the caps holding the carrier in said gm 8703 276 n. does this mean anything?
There are numerals/letters stamped on the axle tube that will have some info. Counting the teeth or looking on the edge of the ring gear for the tooth stamping will give the ratio.

If the rear end is original, often (in newer trucks) the axle is on a code in the glove box.
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  #23 (permalink)  
Old 03-21-2010, 12:58 PM
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Are you asking about the truck 12 bolt or the truck 10 bolt? The internal parts for the 8.5 10 bolt are the same between truck and car rear ends. The truck 12 bolt uses different parts than the car 12 bolt. If you have a truck 10 bolt then the only differences will be the width, axle bearing size, axles and brakes.
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Old 03-21-2010, 05:00 PM
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i picked up the 12 bolt. it says gm64 on the housing. im assuming its out of a 64 car. i have new axle seals but i was told i mine as well replace the seal up front by the pinion shaft. how do i remove this seal and will it require me to make adjustments?
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Old 03-21-2010, 05:05 PM
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i disassembled the 12 bolt and the posi carrier has these numbers stamped into it Edb-30174. i believe this means that its a series 4 carrier.
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  #26 (permalink)  
Old 03-21-2010, 05:07 PM
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12-bolt car rears didn't exist yet in 1964, didn't come out until 1965. Sounds like you still don't know what you have. Go to a site like Randy's Ring and Pinion, there are picture charts that show what each rear looks like.

It is obvious once you have seen the pictures what is different about the car and truck 12-bolt covers.
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  #27 (permalink)  
Old 03-21-2010, 05:15 PM
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Quote:
Originally Posted by dman0712
i disassembled the 12 bolt and the posi carrier has these numbers stamped into it Edb-30174. i believe this means that its a series 4 carrier.
You will know what carrier you have by the gear ratio and width of the ring gear and/or if it has a spacer.

Most ring gears are also stamped w/the tooth count of the R&P, like 13-42, etc.. If not, just count the teeth...
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Old 03-21-2010, 05:30 PM
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its got the cover of a camaro 12 bolt. I looked at pics. it has 4:10 gears and a series 4 carrier
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  #29 (permalink)  
Old 03-21-2010, 06:01 PM
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Quote:
Originally Posted by dman0712
its got the cover of a camaro 12 bolt. I looked at pics. it has 4:10 gears and a series 4 carrier
Lucky you!
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  #30 (permalink)  
Old 03-21-2010, 06:10 PM
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Quote:
Originally Posted by dman0712
its got the cover of a camaro 12 bolt. I looked at pics. it has 4:10 gears and a series 4 carrier
Is it set up for leaf springs, or does it have coil perches w/the control arm pickup points on the center section?

If you got a Camaro rear end, and not "just" a 12-bolt car rear end (the covers are similar, IIRC) then you got something.

I don't know what you are putting this in, but they came in 1st. gen F-bodies and won't fit w/o spring perch mods into a 2nd. gen F-body.

I'd suggest you not cut it up, it's worth way more as-is (if it's an F-body rear. Or even an A-body).

I'd sell it and buy a new "whatever" to fit the vehicle.
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