[dana44]

If you had this engine behind a 7.25, I would expect you to be 95 years old, frail, have cataracts and have difficulty lifting a bag of peas. In short, I believe we all talked about this before, drive gentle (major emphasis) and she will be OK, but step on her or shift at high rpm, forget it. The purpose of the posi compared to a single legger is the third member can shift from one side to the other and in the process snap axles, especially under higher torque of this engine.

 

[dana44]

An automatic Hemi had an 8.75 behind it. That should be enough reason to figure it is strong enough.

 

[dana44]

Agree. The small bolt pattern 8.75 is easier to find and a direct bolt-in, most prefer to move up to the larger bolt pattern on the A bodies, so that would actually be an advantage you have. These days, there are a lot more tire/wheel selections available, you would want the rims to be offset to fit the wheelwells.

 

[dana44]

The A body 8.75 small bolt pattern are easier to find than the large bolt pattern A body 8.75s. Once the housing is located, the third member can easily be swapped from any 8.75 or gear ratio changed without a problem, there are two pinion sizes, based on the case number, I think it is pre-69 and post 69 for the larger pinion.

 

[dana44]

There are locations on the web that show which rear ends are direct bolt-ins, I think it is just about every A body after 1965 or something like that. Going Moser can be a little expensive, but if money isn't the issue, it is correct. An 8.75 has a pumpkin that bolts to the front of the case and the axles have to be pulled to remove it (others do too, but the gears remain part of the case), and I think it is 14 nuts that hold the pumpkin on, the others have a rear cover.

 

[dana44]

Agree, the third member gear set/limited slip portion is swappable, you need the housing right now and can deal with the rest later.

 

[dana44]

Yes, the 741 case and the other is the 489.Both are fine, the 489 just has a larger pinion but is still very strong. From there you can change this 741 or 489 case and gears to anything you want, right now it is the housing and axles (axles can be changed if you want), but there is nothing wrong with the 741, yours just happens to be the cone style posi which will still hold up to the 500hp engine a lot better than the 7.25 you have.

 

[dana44]

Well, 3.73 is a little high for the street/highway but from show to show you could live with it easily enough, better than 4.10s. You are going to have to compare and measure what you have with what is there, from the backing plates out, not sure what you have or whether or not it will work, Verify the width center to center of your springs, the outside of one side and the inside of the other at the rear of the car will make it easier, see if it is the same, the extra 11 inches is minus 2.5 for the spring width which gives you 8.5 inches, divided by two, which should be 4.25 inches clearance between the backing plate to the inside of the wheel stock, which is about right. Now that I think about it, your rear/axle setup is the 7.25 and the rear ends are completely different from each other, not even sure if the brakes are the same size. What components did you actually end up getting?

 

[dana44]

Agree, it is a more common pattern and since the cost of the axles themselves would more than be greater than the front disc upgrade, go that direction. The disc brake setup on the A bodies is the larger pattern to begin with, so most end up changing the axles to the larger pattern on the rear axles to match, not the other way around.

 

[dana44]

The '63 through '72 A-Body 7 1/4 axle measures 53.2 inches from axle flange to axle flange, while the '62 through '70 B-Body 8 3/4 axle measures 55.0 inches from axle flange to axle flange. In addition, the leaf-spring center to center spacing of the B-Body axle is 44 inches, one inch wider than the 43-inch A-Body dimension.

Read more: http://www.moparmusclemagazine.com/techarticles/drivetrain/mopp_0404_8_3_4_rear_axle_housing_swap/viewall.html#ixzz2FjPVmHCi

The dimensions are online, so it looks like you ended up with a B body rear end, so maybe you can take it back. The article here shows a lot of information, and a search will give all the different models and rear end swaps available. Time to do some more research.

 

[dana44]

If you are familiar with some brand of cars, it is a matter of researching and reading what you know but need to apply to a different brand. I did a simple mopar rear end dimension search and found this information and picked it because I have seen it from the magazines themselves. There is a ton of information with the magazine, by the way, including all the K member information, disc brake swap stuff, you name it. There are lots of people that like to show you the information they have or found and compiled, so suggest, as an idea, do some internet searches and comparison articles to verify (not everything on the internet is good), but two or three articles talking about the same thing is usually pretty reliable. As far as Dr. Diff goes, I think shopping around a little bit would be a good idea. Granted it is a new rear end housing and all, but you should be able to save some money on a used one. The pumpkin does fit all the 8.75 housings no matter what car they came out of. I would hit a few junkyards in the area, craigslist, ebay if you like that, used cars (ones with no title can have a lot of good parts, so get a good bill of sale and scrap what you can't use or sell), be creative.

 

[dana44]

Should be able to, B body stuff isn't cheap any more. Do the measurement verification stuff, listed above for you. Don't worry about the axle bolt pattern at this time, get that housing, complete if possible.

 

[dana44]

Sounds like you read the link I added to my last post, it does describe how to make what you said work, I have moved perches before, just have to be careful a bit, don't want warping or anything, so take it slow, good tack welds, add a little more, little at a time. The only thing that needs to be addressed, which the article notes, is the offset to the rear wheels so the whole wheel well can be utilized, which the article does talk about and show examples. These days, custom wheel backsetting can be ordered without a problem.