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Old 12-21-2012, 07:30 PM
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8.5 or 8.2?

My 41 came with a GM 10 bolt of unknown origin. Based on the drums, wheel cylinders, etc., I am thinking it is an 8.5 Oldmobile supplied out of a 73 vintage Chevelle, Cutlass, or Skylark based on the following information:

1-1/4" Pinion nut
30 spline pinion
28 spline axles (non c-clip - there's the rub)
2.41:1 gear (41-17)
11" drums
15/16" wheel cylinders
Upper trailing arm mounts are still on the housing (part of the center section casting)
So it was a coil spring rearend that has been converted to leafs.

I also have the remnants of an 89 Chevy pickup. It has an 8.5 with a 3.42:1 gear and 30 spline axles.

I want to put the carrier with the 3.42:1 gears from the truck in the 41 housing. I intend to put a Powertrax 1920-LR locker in it.

The rub is the non c-clip axles. The outfit I am wanting to buy the parts from is convinced the non c-clip rearend is an 8.2 BOP.

So, I am trying to figure it out. Tomorrow, Saturday, I intend to see if the rear covers will interchange. My question is, will this tell me anything? In other words, will an 8.2 cover fit an 8.5 rearend? If not, if they do interchange, does that pretty much guarantee they are both 8.5's?

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Old 12-21-2012, 08:59 PM
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iirc the olds is the only non c clip..
it's not a b-o-p rear, it's olds

my 74 buick had c clips..
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Old 12-21-2012, 10:08 PM
Will I ever get it done?
 

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The 8.2 BOP was non c-clip. I had several mid 60's Pontiac A bodies with that 10 bolt and they were all non c-clip.

Also muddying up the water is the Olds 12 bolt which has a 12 bolt cover with a 10 bolt ring gear. It doesn't interchange with anything.

The 8.5 is supposed to interchange but the 30 spline carrier requires special bearings to be put in the 28 spline housing.

Does anyone know for certain if the 8.2 cover will physically fit on the 8.5 rear end?
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Old 12-21-2012, 11:00 PM
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The '71 and '72 A body 8.5 10 bolt did not have c clips. This is the only version of the 8.5 that had this type of axles. It was used in '71 and '72 Buick and Olds A bodys. There are rumors that it made it into a few Chevelles, but I have not seen one. As far as I know the Pontiac A body continued to use the BOP 8.2 10 bolt through '72. All corporate 8.5 parts will fit this rear end except the axles and brake backing plates. The Chevy 8.2 cover will interchange with the 8.5 cover, but might not fit this A body rear end. All 8.5 corporate rear ends had a 30 spline pinion.

The BOP 8.2 has a 27 spline pinion and the cover will not interchange. The axles also will not interchange because the splines are not the same.

The O rear end was used in the Cutlass from '68 to '70 and had a 12 bolt cover with 10 bolts in the 8.5 inch ring gear. This is not the same as the corporate 8.5 rear end and parts do not interchange.
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Old 12-22-2012, 01:35 PM
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You probably have a 8.5 center with Olds-type axles. There are two Olds axle bearing/seal configurations so match up your old parts if you replace them. Regular 8.5 bearings and gears will service your center diff components.
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Old 12-22-2012, 05:00 PM
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Quote:
Originally Posted by big gear head View Post
The '71 and '72 A body 8.5 10 bolt did not have c clips. This is the only version of the 8.5 that had this type of axles. It was used in '71 and '72 Buick and Olds A bodys. There are rumors that it made it into a few Chevelles, but I have not seen one. As far as I know the Pontiac A body continued to use the BOP 8.2 10 bolt through '72. All corporate 8.5 parts will fit this rear end except the axles and brake backing plates. The Chevy 8.2 cover will interchange with the 8.5 cover, but might not fit this A body rear end. All 8.5 corporate rear ends had a 30 spline pinion.

The BOP 8.2 has a 27 spline pinion and the cover will not interchange. The axles also will not interchange because the splines are not the same.

The O rear end was used in the Cutlass from '68 to '70 and had a 12 bolt cover with 10 bolts in the 8.5 inch ring gear. This is not the same as the corporate 8.5 rear end and parts do not interchange.

Quote:
Originally Posted by lmsport View Post
You probably have a 8.5 center with Olds-type axles. There are two Olds axle bearing/seal configurations so match up your old parts if you replace them. Regular 8.5 bearings and gears will service your center diff components.
Checked a few more things today. I think you both are right. At this point, the only problem I have is with 72 being the cut-off year. From what I can tell, the 11" brakes were not available until 73.

The ring gear bolts have 3/4" heads and I believe the "L" on the heads indicate they are left hand thread.
The side gears, pinions, and cross shaft from the truck rear end fit in the rear end of the 41 perfectly.
The outer race on the axle bearing in the 41 is a Timken U261L which should be correct for the Timken Set 9 bearing that the Olds Cutlass used.
The truck rear end cover bolts on the 41's rear end perfectly.

With all of this plus the 30 spline pinion, I am convinced they are both 8.5 rear ends (the truck may have an 8.6 gear but I don't think it makes a difference).

So, I am thinking about putting the Powertrax 1920-LR in the truck carrier and putting it in the 41 housing along with the 3.42:1 gears using bearings LM102949 and races LM102911.

Or, would it be worth the extra money to buy a complete carrier from Auburn, Strange, or Detroit? The car is going to have a mild 350 / Turbo 350 combo.
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Old 12-22-2012, 05:17 PM
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An 89 model truck would use the same carrier bearing. The carrier bearing was not changed to the 603049 bearing until 1998.
I'm not a fan of the Powertrax for street cars due to the general harshness of their operation. I prefer the Eaton posi if given the option. Detroit locker if the hp goes beyond 600.
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Old 12-22-2012, 05:31 PM
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Unless you have a mean 350 I think both rears are strong enough, but I would use the truck one.
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Old 12-22-2012, 08:54 PM
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Yea, the '89 uses the same small bearing as the earlier 8.5. The Eaton Posi will use the LM102949 and LM102911. I would also use the Eaton Posi.
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Old 12-22-2012, 10:48 PM
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The 19557-010 Posi or the 912A556 Trutrack?
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Old 12-23-2012, 06:51 AM
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Either will work fine for what you have, Eaton Posi or Eaton/Detroit TrueTrac.
Yukon DuraGrip Posi will save you some $$, it's a copy of the Eaton Posi.
Quick Performance has them cheap:
GM 8 5" 10 Bolt Posi 28 Spline Limited Slip New | eBay
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Old 12-24-2012, 08:37 AM
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The money saved with the DuraGrip is not significant enough for me anymore. I have had 3 Yukon break the case in two in the last couple years. 1 Ford 8.8 and 2 GM 8.5, all in street cars with roughly 500hp and street tires. FWIW, two broke while at the dragstrip.
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Old 12-24-2012, 09:07 AM
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I wanted to take back my coment about the '71 and '72 A body 8.5 being the only one with the bolt in axles. I have found out that there were more of the 8.5 rear ends that had this type of axles, so you are probably right about your rear end being a '73 or later.

Imsport, these were Dura Grip cases that you broke? I'd like to know more about this as I have sold many of those differentials.
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Old 12-25-2012, 02:25 AM
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1st problems I've heard of with the DuraGrip.
I haven't had any problems with the DuraGrip in my 12-Bolt. It's also seen quite a few Trans Brake launches.
I did do this Mod to it during a Gear change but, I doubt it changed anything pertaining to Case strength.
How to Rebuild a Used Posi - Car Craft Magazine
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Old 12-25-2012, 11:18 AM
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[QUOTE=Imsport, these were Dura Grip cases that you broke? I'd like to know more about this as I have sold many of those differentials.[/QUOTE]

X2.. I install 2/3 of these a week and I've yet to have one of these back for breakage. I've used a pretty good volume of these and would not hesitate to use them.
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