Rear end dimensions

[steve from staten island]

I have a 8 3/4 rear which has the 742 case and a 355 ratio with sure grip. The rear was suppose to be out of a 66 b body which puts the drum to drum length at 59 1/2 inches
I want to use this rear in a 69 B body which calls for a 60 1/8 drum to drum rear.
Aside from moving the spring perches and the obvious difference would it be recommend to use this rear, given the total difference is 5/8 of a inch which puts the drum to drum difference at 5/16 each side. Any thoughts/comments? Thanks

 

[dsd1967]

You won’t need to move the spring perches. They’re the same spacing from 66-70. It will be a drop in. Unless you are trying to maximize tire size it will be a seamless install

 

[Jerry Hall]

You won’t need to move the spring perches. They’re the same spacing from 66-70. It will be a drop in. Unless you are trying to maximize tire size it will be a seamless install

I was sitting here wondering why the spring perches would have to be moved. That had never even crossed my mind when looking for a 8 3/4 for a B body project.

 

[steve from staten island]

So the difference in drum to drum length is not a problem

 

[dsd1967]

With a somewhat standard tire you won’t have an issue. If you want to put wide tires on then you will have to pay attention to backspace.

 

[dsd1967]

If you are using a stock rim you will not have to worry. You can’t get a wide enough tire to cause an issue. In fact the inner wheel tub to wheel tub distance is the same. I just put a 69 charger floor in a 67 Belvedere. The inner wheel tubs are the same from 66-70

 

[steve from staten island]

With a somewhat standard tire you won’t have an issue. If you want to put wide tires on then you will have to pay attention to backspace.

I have 235 60. 15 tires on there now...Will look at how close they are to wheel wells.....Thanks

 

[33 IMP]

Steve, if anything, the slightly narrower rearend is a big plus. It opens up wheel selection choices, making backspace not quite so critical.
I have at least three pairs of vintage wheels that are almost un-usable because of too much offset to the outside, the right width tire for the width of the rim rubs the outer fender.
The effect of a narrower rearend is to move the tire closer to the leaf springs. IF, IF the tire ends up too close, spacers are an option. Im not scared of spacers at all, i use spacers on a 11 sec street car and a 9 sec racecar.

 

[66Satellite47]

Wheel backspace is the key, like always. 325's should fill the wheel wells.

 

[mopar 3 B]

If really worried retain your original housing and axles. The differential will fit just fine. You may have to change the center spacer. If that is the case just use the one from the original differential.

 

[74RR]

Can someone answer if this is an 8 1/4 or 8 3/4 rear end? I thought the 8 3/4 had the bolts on the front with the whole gear assembly being able to come out. This I would suggest is an 8 1/4. Looking for advice. Thanks all.

 

[74RR]

Can someone answer if this is an 8 1/4 or 8 3/4 rear end? I thought the 8 3/4 had the bolts on the front with the whole gear assembly being able to come out. This I would suggest is an 8 1/4. Looking for advice. Thanks all.

 

[66Satellite47]

Not a 8 3/4.
Could be 7 1/4, 8 1/4 or maybe even 9 1/4 depending on physical size.

 

[33 IMP]

Absolutely certain it is NOT an 8 3/4 (nor a dana 60). Never having had either an 8 1/4 nor 9 1/4, i cant be sure, but i think (think!) It is a 9 1/4. If it is, it is an excellent, strong rearend, with virtually no hop-up parts available. (In other words, aftermarket gears and suregrips virtually nonexistent).

 

[33 IMP]

It is a 9 1/4. Google "mopar rearend identification chart".
Edit. Did some research, parts are available for the 9 1/4 twelve bolt. (Do not confuse with gm twelve bolt). Surprised me!
Motive gear has gear sets from 3.55 to 4.56, and Yukon gear sells a dura grip lsd. Gears and a "posi" will run $850+.

 

[Jerry Hall]

 

[66Satellite47]

Jerry, thanks, I couldn't find that chart quickly. I completely forgot that the 8 1/4 had the obround cover.
9 1/4's are very strong. If it is a factory limited slip, would be outstanding.

 

[oldkimmer]

It’s not out of a 66 car unless it’s an Imperial. Some Imperials had them with disc brakes. Kim

 

[74RR]

I was told it was from a 74 Station Wagon. I really appreciate the fast response from you guys! I'm considering buying it "to put on the shelf" should I ever need a rear-end swap. What's it worth given the gears are unknown? Seems to be posi. Again, details are quite vague from the seller.

 

[33 IMP]

If it is a "posi" (there are fanatics here that will crucify you for that, its a "sure grip" ) and it turns, its easy to find out what gear it has. Just turn the pinion till an axle makes one ful turn.
A sure grip with 3.23 or 3.55 is worth a bunch more than a 2.76 open, especially if it is a bolt in for your car.
Compare drum to drum widths.