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NEED HELP WITH DIFFERENTIAL SWAP


Julian Sepulveda

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I own a 1970 skylark with gm 8.2. I am currently looking to swap to a gm 8.5. A friend told me that a good swap would be to take a differential from a 77 cutlass. 

 

Question 1: Will this be a direct bolt in? If not, how much would it cost to adapt it to fit? Is this worth the effort or should I look for a different one?

 

question 2: Are any parts interchangeable between the two? I remember reading that the axles and shoe brakes are interchangeable, as they are both bolt in axles, but this sounded like fishy information.

 

Question 3: If this differential will not work, what would be a good donor car to find a proper differential? 

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In order to try and assist you, it would be helpful to know why you wish to make this change. Both the 8.2 and 8.5 are "10-bolt" GM rears. The 8.5 has a larger pinion diameter, and is a little beefier than the 8.2". So would it be safe to assume that you are wanting to install a stronger rear axle assy, which can withstand greater torque under launch, etc? 

 

If so, personally I would simply spend a few more bucks and buy a 12-bolt out of a Chevelle, (or more commonly-found in a 1970-72 Monte Carlo). 1968-72 will pretty much bolt right in. You will need to check the u-joint size at the pinion flange...since the 12 bolt might be sized for larger U-joint bearing caps. Otherwise, it is a piece of cake. Used 12-bolts are still out there (again, easier to find one in a Monte Carlo, as many muscle car guys seldom think to check those), and they are no longer as expensive as they were a few years ago...at least around here. 

 

The 8.5 rear end was found in many GM cars and light pickups starting in 1970 and through the 70's (except Cadillac). But it sounds like you are seeking something which will bolt in with little or no modification. 

 

I found a really good article about that 8.5" rear end. Here is a link: GM 8.5" rear end article

Edited by lump (see edit history)
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The bonus with using a Buick housing and axles are that they use a regular ball bearing axle bearing. Chevy 12 bolt rears use Hyatt style roller bearings that use the axle shaft as the inner bearing race and " c " clips for axle retention. Heavy duty use or high mileage can result in axles that wear in the bearing area and need replacing.  Many consider the Buick design superior.

Greg in Canada

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