What 8 3/4 rearend do I have?

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augiepaw

augiepaw

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I picked up a 8 3/4 rearend from a junkyard and want to know if someone knows what it is? It was sitting loose and not under anything, so I'm not sure what it came out of. The casting no. is 2881489 with a big 9 behind the casting no. It measures 59 1/2 from outside of brakedrum to outside of brakedrum and the best I can tell 41 3/4 from inside of the spring perch. I got it for my 71' Demon, but I think it is to long. Any help? Thanks
 
Well, the first thing you can do is check to see if the bolt pattern on the axles is 4 inch or 4.5". A body 8 3/4 rear ends only came with the 4 inch bolt pattern. I just measured the inside to inside of the spring perches of the A body housing on my bench and it measures 40 1/2", leading me to believe that you have yourself a B-body unit from a 69 or 70 car. B body rears from pre-71 cars measure 44 inches from the center to center of the spring perches, where they are typically measured. The 489 case replaced the 742 case during the 1969 model year, so if your rearend has not been altered and is in as removed condition, I would say that it is a late 69 or 70 B body piece. It could still be used in your demon, but you will end up with LBP axles and offset rear rims, like a lot of guys are doing here due to the elusive A body units. Trouble comes in when your fronts are still small bolt!!! Unless of course that has been changed out already. Hope all of this helps!!! By the way, is it a sure grip??? Good luck with your project, Geof
 
So its most likely a B body. The bolt pattern is 4 1/2" on the rear end and I measured 44" from center to center on the spring perches. I do believe it is a sure grip. I'm not sure how to tell. With out tearing it apart and looking. The gears are 3.23. Am I better to keep looking or try to make this one work? If I try to make this one work, what mods will I need to do? I'm far from needing one now. I do have plenty of time to come up with something else. Thanks
 
For telling if it's a Sure Grip, get someone to hold the opposite side axle (hold it solid) , it will turn in the same direction if it is a Sure Grip.
There is only one way to tell otherwise, it will have a "red" fill plug, which likely is not red anymore. Casting numbers etc... won't tell.
 
I have never done this myself, but being you have a B body, one inch wider at the springs (1/2" per side) then an A body, it's been done commonly as a bolt in, the back spacing of rims then becomes an issue with wider tires.
You also have a "489" case the strongest of the 8 3/4" difs.
 
I guess you are going to have to come up with a plan as to how you'd like to proceed. Do you want LBP on your car? Is the front drum or disc? IMO, the best case scenario for you would be... if you had drum in the front, make a plan to change to the later style LBP disc up front and use the rear you have and just get some rims with a little different backspace. If you already have disc up front and you don't want to change, you would be looking at finding an A body unit with small bolt axles and use the center section from the rear you have, especially if it's a suregrip. Good luck with your project, Geof
 
That is a good thing right?? I'm not sure what to do? Anyone needs a 8 3/4" "489" B body rearend? Am I understanding you right? Being a 1/2" wider on both sides it still a bolt in? The only issue is what rims I can put on it. Thanks to all for your help!! Chuck
 
I'm going to put disc on the front, but as of yet it still drums. And I'm sorry to sound so dumb, what is LBP?
 
large bolt pattern (4.5 inches)
...desirable because it opens up the available wheels
with that particular rear end (B-body) you can bolt on the mustang bullet
17 inch wheels and about a 275 x17 tire...(or bigger, just measure)
switch the front over to 4.5 (lbp) and with a 73 & up upper control arms
and maybe a 1/8 inch spacer and the same wheels will fit up there..
you really should move the spring perches in but i have seen folks who didn't
 
I really like to get it to work if I can. Clark, I have your number if I decide to sell it. Thanks to all and Happy Thanksgiving
 
Get wheels with a bit more offset and you'll be fine. Move the perches in 1/2" on each side or stretch the springs outward and it works.

The longer 68-70 rears are installed in a bodies all the time.
 
crackedback said:
That chart butter put up is so wrong...

Here is a better source with CORRECT lengths.
http://www.moparts.org/Tech/Archive/axle/16.html

It's a 65-67 B most likely

I wish someone would get rid of that crappy chart, it's all over the place and not worth the pixels to display.
Click to expand...

I agree, there is some incorrect info on that chart.
I posted it because of the schematic, it's easier to see where the dimensions come from for new folks.

Maybe I should try to make one with the correct dimensions.
 
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