rear diff decoded - Nova Tech
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  #1  
Old Dec 17th, 19, 11:55 AM
mrgasket mrgasket is offline
 
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Default rear diff decoded

I know someone here can help me decode this 10 bolt 8.5 GM diff.
it appears to have factory disc brakes,the casting #s are 1249618B,
GM 13 or GM18,K38 with the clock thing. On the crown 15,14,11,76.

those are all of the #s i could find.
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  #2  
Old Dec 17th, 19, 12:42 PM
ramportin1 ramportin1 is offline
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Default Re: rear diff decoded

novaresource.org/axle.htm
This should help

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  #3  
Old Dec 17th, 19, 12:42 PM
Big Dave Big Dave is offline
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Default Re: rear diff decoded

10 bolt corporate (AAW 8.5 inch ring gear) with disc brakes were installed under a Cadillac Seville (X-body same as the Nova) from 1976-'79, and under first and second generation Camaro with the JL8 brake option (very rare option); or the second Firebird SE with the WS6 suspension option which is much more common. Neither of the second gen F-body rears will fit under a X-body as they are too wide and the spring perches have a different pigeon toed spring mounting angle. The first gen Camaro JL8 rear is worth more to a Camaro restorer than the value of your Nova, as they were normally installed on factory prepared Trans Am race cars.

Odds are it is out from under a Caddy. Bad news is those brakes only work if they are maintained: which is why they were discontinued, as every knows a Caddy owner can not be expected to do maintenance on their cars. Without constant adjustment the brakes will nor work at all, so they were involved in a lot of wrecks. And unhappy Caddy owners.

The third gen IROC Camaro were fairly common, and they had rear disc brakes. Nut that rear end was a coil spring mounted triling arm suspension with a 7.5 inch ten bot ring gear that will not fit under a Nova without a lot of work. The brakes will however bolt up to any ten bolt, so the brakes may have been swapped off of another car as opposed to being a factory install. Which brings up the point that GM used five different brake manufactures for their rear brakes. What you have can be identified by part number or casting numbers. Brakes were based upon four piston Girling, or Brembo, or the two piton PBR using a fixed bridge, or two different GM designed single piston full floating brakes.

Big Dave
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  #4  
Old Dec 17th, 19, 10:56 PM
mrgasket mrgasket is offline
 
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Default Re: rear diff decoded

[QUOTE=Big Dave;318551]10 bolt corporate (AAW 8.5 inch ring gear) with disc brakes were installed under a Cadillac Seville (X-body same as the Nova) from 1976-'79, and under first and second generation Camaro with the JL8 brake option (very rare option); or the second Firebird SE with the WS6 suspension option which is much more common. Neither of the second gen F-body rears will fit under a X-body as they are too wide and the spring perches have a different pigeon toed spring mounting angle. The first gen Camaro JL8 rear is worth more to a Camaro restorer than the value of your Nova, as they were normally installed on factory prepared Trans Am race cars.

Odds are it is out from under a Caddy. Bad news is those brakes only work if they are maintained: which is why they were discontinued, as every knows a Caddy owner can not be expected to do maintenance on their cars. Without constant adjustment the brakes will nor work at all, so they were involved in a lot of wrecks. And unhappy Caddy owners.

The third gen IROC Camaro were fairly common, and they had rear disc brakes. Nut that rear end was a coil spring mounted triling arm suspension with a 7.5 inch ten bot ring gear that will not fit under a Nova without a lot of work. The brakes will however bolt up to any ten bolt, so the brakes may have been swapped off of another car as opposed to being a factory install. Which brings up the point that GM used five different brake manufactures for their rear brakes. What you have can be identified by part number or casting numbers. Brakes were based upon four piston Girling, or Brembo, or the two piton PBR using a fixed bridge, or two different GM designed single piston full floating brakes.

Big Dave[


Big Dave thanks for all the info
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  #5  
Old Dec 20th, 19, 02:01 AM
Elvis Elvis is offline
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Exclamation Re: rear diff decoded

Quote:
Originally Posted by mrgasket View Post
I know someone here can help me decode this 10 bolt 8.5 GM diff.
it appears to have factory disc brakes,the casting #s are 1249618B,
GM 13 or GM18,K38 with the clock thing. On the crown 15,14,11,76.

those are all of the #s i could find.
If you're trying to decipher the gear ratio, take the cover off and spin the ring gear.
Eventually, you'll come across some writing on the edge of the gear.
Some of it will be two sets of numbers separated by the ":" sign (sorry grammaticists, I fergit right now).
Grab your phone, or the nearest calculator and divide those two numbers and you'll have your gear ratio.
For instance, if it says "37:11" just divide 37 by 11 and you'll get 3.3636363636....aka 3.36 gears.
Found that back when I owned a '73 Vega and had to replace the spiders (don't ask ).

Elvis
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Old Dec 20th, 19, 09:52 AM
Big Dave Big Dave is offline
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Default Re: rear diff decoded

If you don't find numbers stamped into the ring gear edge (It happens sometimes with aftermarket parts) then put a crayon mark on one tooth and count the number of teeth to get the same information.

Hard to believe that GM re-used the same Vega rear end under all third gen Camaros and up. Designed for a four cylinder but put behind an LS-x engine. Good news is the ring gear jumped from a 7.5 inch all the way up to the maximum size that will fit in the case of 7.6 inches.

Which is why I use a 9 inch ring gear Moser S60 Dana rear end under everything I build for my use. I have never broken one and they are used under Pro Stock cars that launch harder and have more power that anything I have ever built without a Roots blower on top.

Big Dave
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  #7  
Old Dec 20th, 19, 12:04 PM
Elvis Elvis is offline
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Default Re: rear diff decoded

Well, to be certain, Mr.Gasket's 8.5" rear end will be a little beefier than the one featured in my old Vega, but I just wanted to interject that there's another way to decipher what gear ratio you're running, aside from trying to chase down a bunch of codes.

Elvis
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  #8  
Old Dec 21st, 19, 12:40 PM
mrgasket mrgasket is offline
 
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Default Re: rear diff decoded

thanks for all the help,this site is awesome
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