‘73 Dart Sport Rear End Upgrade

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John Collins

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I’m looking for advice on which route to take. I currently have the stock 7 1/4 rear end. The previous owner upgraded the engine to a 360, but kept the weak 7 1/4. What is the best option for an upgraded rear end? Best being affordable and also available with a little luck. I’ve been looking around and 8 3/4’s in SoCal are nearly impossible to come by, especially big bolt pattern A body rear ends. Is it best to find a B body rear end and have it shortened? Also, if there are any SoCal folks on here reading this, where’s some spots that might have 8 3/4 rear ends? Everywhere I’ve called is expensive AF for just the diff. Any help would be appreciated.
 
You can probably get a B body 8 3/4 under there by moving perches and different backspace on the rims

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John Collins said:
Is it best to find a B body rear end and have it shortened?
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I didn't shorten mine. B body rear with 10" wheels with 5.5 inch backspace. I completely rebuilt the rear with new gears, all new brake hardware, axle bearings, used clutch type sure grip, moved the perches in to equal the 43" on center for the springs, etc.

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leblanc said:
I ran the original 7.25 for about 5 years before changing.
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I just bought this car about two months ago and haven’t driven it much. There’s a slow leak in the diff and I was contemplating rebuilding it, but after research decided to change it out. I’d go with an 8 1/4 as well, but I want to try and wait it out a bit first for an 8 3/4. I don’t think I’ll ever have a monster engine in this car, but my friends with A Body Mopars all suggested going with an 8 3/4, if I can find one for a fair price. I’m not trying to spend $2500 for a rear end on a car I paid $8k for that has no major upside in value. I guess I’m hoping to get lucky and find something needing a little TLC.
 
8 1/4 rear in my dart sport 360. Drove for a good while with 2.45's! They sucked but had no choice. Funds were tight. Then slowly as funding permitted. Found some 3.91's on ebay for like $150 new US gear brand. Then an auburn suregrip from a member on here also new in box. And the difference was night and day!! Car is much more alive. Revs higher but moves quicker.:steering:also have heard that the 8 1/4 can handle @ least 500 horsepower. Not sure though.
 
I found a big bolt pattern 8 3/4 rear end on this page. It’s a b body, but perches have already been moved to suit the A body and it’s only 2” wider, flange to flange. It’s an open diff, but it’ll get rebuilt and upgraded when I can afford to. Thanks for the input everyone!
 
Just ordered a new helical sure grip from Doctor Diff. to go with the new to me 8 3/4 rear end. I’m picking up the rest end right now and the Helical unit ships tomorrow.
 
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