Narrowing rear diff.

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Demonseed

Demonseed

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I'm working on a 72 Demon. The rear springs have been moved in with mini tubs. I want to run a 15" X 10" wheel with 4.5" backspace. Prefferably a 28" x 12.5" tire. Does anybody have an idea of how much the rear diff. needs to be shortened on each side? I would greatly appreciate the input.
 
I ran 15" x 10" with 5.5" backspacing and endeded up narrowing about 2.5" inches so 1" less backspace means narrowing it 1" more, so 3.5" I would not take a guess at this-bad things can happen!!!!! I would recommend getting your tires/wheels mounted, set them up under the car where you want them to sit and measure inside rim mounting surface to opposite rim mounting surface measure several times, then call the Diff Dr., the man knows the spacing and figures in his head very nice to deal with and had my parts fast. hope this helps
 

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Put the wheels and tires under the car where you want them to sit and measure.

That's the best and correct way to get the rear exactly right on length.

Here's a question close to yours.

What color shirt am I wearing today?

You don't know.

Just like nobody can tell you how much to cut off a rear of unknown length.

As a guess, it's going to be about 50-51" total width
 
Like 76oragewagon said, certain wheel width and backspace numbers equal corresponding hub-to-hub housing numbers. It's just math. You can figure it out with the numbers or you can figure it out with the tape measure. If you don't know or understand the numbers, mock it up and take measurements. Either way works fine.

Don't forget the axles!
 
This is a guy I know that lives pretty local. Pretty sure it's a 28x13.50 ET street
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My Duster rear is 49" overall with a 15x10 wheel w/ 3.5" backspacing... car is mini tubbed...

hateduster1.jpg
 
My buddy with the Long Ram Dart ran 28x11.5s on his stock length rear.

He had Stockton Wheels make him up some sbp 15x11 rallyes with a bit of back spacing.

Check out the depth of the trim rings and the inside bead of the rim in relationship to the stock spring perch.

PA241350.jpg


PA241349.jpg


PA241348.jpg
 
I just ran across my notes for my 70 Swinger. The rear is stock length A body with a 15x8 Bogart with 6 1/8 backspace. I run a 28 11.5 ET street. Its tight but it fits and barely rubs when going into extreme driveways. My guess 6 inches. I would measure for sure.
 
Demonseed said:
How much do you want for the rights to it?
Click to expand...

Not for sale but I'll rent it to ya, besides having another seed here allows me to blame you whenever I screw up like calling a member an A-hole (which of course I'd never do) or better yet buy something in your name. Yea, you can be my backstop. Ain't plausible deniability great. These guys think one Demon Seed is one to many, wait till they see the confusion 2 of us can cause.:toothy10:
 
I had a C-body housing narrowed to 46 5/8 (A-body housing is 52 5/8,minus brakes)so basically 3 inches either side of A-body length.I fit 15x10,s and 15x12 under my 66 Dart with a minitub and 3 inch spring relocation.Rims are 4.5 b.space
 
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