[Charlie Brengun]

I'm trying to figure out what kind of rear axle lives under my GTO. It's not a BOP 8.2 as it's missing the cut outs at the sides.
I think it's an 8.5.. I hope it is, cheaper to rebuild an 8.5 then replace an 8.2


Here's a couple pictures.

http://i10.photobucket.com/albums/a1...O/IMG_3740.jpg

http://i10.photobucket.com/albums/a1...O/IMG_3739.jpg

http://i10.photobucket.com/albums/a1...O/IMG_3737.jpg

http://i10.photobucket.com/albums/a1...O/IMG_3736.jpg

[Greg Reid]

This is an Olds site but it identifies all the GM diffs. As you can see, a side view pic would be helpful. Looks like a 10 Pontiac cover but I'm no expert either... If it has the converging ribs on the side, it's def Pontiac.
Just noticed...as you say.... the cutouts are missing?

http://www.oldsmobility.com/reardiffs.htm

http://www.oldsmobility.com/10boltPont-rebuild.htm

[marxjunk]

looks like a chevelle 8.5 to me...

[68gtoMN]

Chevy 10 bolt 8.5, as previously stated. Does not have cut-outs near axle tubes

[Charlie Brengun]

well mine doesn't have the little corners on the bottom. Here's some better pics including some pictures of the ribs on the side..

http://i10.photobucket.com/albums/a1...n/IMG_3743.jpg

http://i10.photobucket.com/albums/a1...n/IMG_3742.jpg

http://i10.photobucket.com/albums/a1...n/IMG_3748.jpg

[marxjunk]

not all 8.5s havre the ears/corners...i have 3ipersonally removedfro 71-72 chevelles and they dont have the ears...every buick rear ive pulle and i have 4 or 5 have the ears..but you can see the cover and its an 8.5 dont believe everything ya read about id ing them, theres a casting number on the housing it tells the story..but im sure its a chevelle 8.5

[Charlie Brengun]

where exactly can I find that casting number? I'll go and look up numbers on the axle tonight. I hope you're right and it's a 8.5.. would make me happy

[marxjunk]

the last pic you posted shows the casting number right there on the casting web next to the axle tube..i can see it but cant make it out

its an 8.5 for the 3rd time

[Charlie Brengun]

thanks that's good news for me, unfortunately these pictures didn't come out too clear. to me it looks like 12343 67880

So the code would also tell me whether it had a posi and what gears it would have had originally?

[marxjunk]

no this pic
i can see the numbers but cant read them..take the numbers and google them it will tell you what it is...as far as gear ratio, its stamped on the tube somewhere

[Charlie Brengun]

ohh okay that's 3969277NF. So that makes it an 8.2 then? or at least if I understand what they're saying correctly http://www.chevellestuff.com/qd/gene..._axle_info.htm

[MescaBug]

That's a Chevy 8.2. Same as the old 8.2 that came with my GTO. When I removed it, I opened it and the guts are different from the 8.5. The cover is definitely not BOP.

The only difference is that yours has U-bolts instead of straps.

[marxjunk]

chevy 8.2s have the scallop on the rear end cover like a 12 bolt..it looks like an arrow pointing up....

[MescaBug]

Mine had the scallop. You can see part of the 'arrow' between the 2 and 3 o'clock position. Charlie's doesn't seems to have it, but I wouldn't use the cover to identify it. Lots of covers fits the 10-bolts... Might have been changed.

[webfoot]

Not all had the scallop. I have 2 68 rears (earlier 12 bolt chevy rears had the scallop too) and they have the scallop. The 2 70 rears I have had did not.

[marxjunk]

ohh okay that's 3969277NF. So that makes it an 8.2 then? or at least if I understand what they're saying correctly

thats doesnt say its an 8.2 it says its a chevelle rear...i have a few rears setting around, ill shoot pics and put the info down

there are 2 8.5s a chevelle and a BOP and they look simular but have differences...but pontiac used the 8.2 til 72 so i dont know why they call it a BOP rear...

the only other smooth cover ive seen is an olds 12 bolt....which is a heavy duty housing with 12 outer bolts but the carrier is a 8.5 but its all by its self

chevelle 12 bolt

BOP 8.2

BOP 8.5

If you read this it says MOST have the humps/ears

moreinfo

[marxjunk]

all of this info is on the web, i still say its an 8.5. chevy stopped using 8.2 in mid 71 ive pulled and sold alot..like 50 chevy 8.5s and they all look like yours so either ive sold them under false pretense(no one ever returned one or kicked my ass)or they are
8.5s...the smooth cover is how i id them..and yours has a smooth cover..the sure way is to pull the cover..if the ring bolts tighten CCW its an 8.5 if they tighten CW its not...theres a code/part number on the ring gear too that can be googled...

so without being there to see whayt ya got...im going with 8.5....not everything in print or on the web is correct...

[webfoot]

That code is for 70-72 chevelle 10-bolt.

http://www.chevellestuff.com/1972/rear_axle.htm

Good info from big gear head:

http://www.chevelles.com/forums/showthread.php?t=318409

[RicksGTO]

There is a lot of mis-information online but the only A-bodies that came with a 8.5" rear end in '71 or '72 were Olds Cutlass and Buick Skylark. Chevelle's used the 8.2 thru '72 unless the 300+hp motors were optioned and then they came with the 12 bolt.

[MescaBug]

Right. GTO's also. All 8.2 unless RA or HO.

Most used cars had the rear end swapped at some point. Can be hard to identify what you have unless you open the housing. No better way to be sure.