Rear End

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Vroom72

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I believe my 72 duster has a 7 and 1/4 rear end but my dad thinks it will not be strong enough. I recently purchased eldebrock performance rpm heads, comp cams cam and lifters, eldebrock performance rocker arms, comp cam pushrods, eldebrock airgap intake, msd distributor and racing rotor, as well as a msd coil. I am purchasing a MSD fuel injection system as well. My car came Stock with a 318 so I was hoping you guys could help me out with the correct rear end choice. I appreciate it in advance!:burnout:
 
First thing is to look at the picture below and figure out which rear end you have for sure. Best way is to start counting bolts on the cover and comparing shapes. I believe the 7.25 also had a 10 bolt version that was more octagonal. Best hope is you have an oval (8.25 or round 8.75)

If you have the 7.25, I would start looking for something bigger.
Good luck.
 

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And if you start looking for something bigger you will need an 8 3/4 with sbp or else do a lbp conversion
 
The 7 1/4 rear is weak, only good behind slant six cars unless you drive like an old lady :glasses7:
 
Would you like a bolt in rear? Or are you willing to do some cutting n grinding is probably the first thing you should ask yourself. Def need something beefier Though if you plan on being hard on it :)
 
The mods you listed aren't going to create a 500hp monster. Unless you plan on install slicks or really sticky, large tires, you're not likely to hook hard enough to break anything.
 
66340SEDAN said:
The 7 1/4 rear is weak, only good behind slant six cars unless you drive like an old lady :glasses7:
Click to expand...


Yep, I blew up three 7 1/4" axles within 4 years in my 68 Barracuda daily driver with just a mild 318 with a 340 cam, 360 heads, stock square bore 340 intake, holley 600 vac secondaries and dual exhaust.

Basically a 318 built to a 340 specs....

The third and last time, the driver's side axle came out on the highway with the tire still bolted to it and passed me on the shoulder at 55 MPH...

I then went to an 8 3/4 sure grip and never had another axle problem, and drove the Barracuda to 500,000 miles before the body got too bad to keep going...
 
Dad knows! It'll grenade right quick.
The 8-1/4 is for mild V8 performance.
The 8-3/4 will handle some real good power. (Will handle 500 no problem.)
The DANA will take it to the crowd and bring home the bacon on extreme builds.
 
Look and see what rear end you really have. I had a factory 70 Duster 318 2bbl 904 with a single peddle 8 3/4. I believe the /6 cars got the 7 1/4.
 
My parts car 73 duster was a original 318/7.25 car. You'd be lucking out if you have a 8.75 like mderoy340!
 
im deployed so I will have to have my wife take a pic for me. I basically have a 340 spec car in my 318. I have spent the money to upgrade everything so Im hoping for 400hp which is why I was asking. A bolt in replacement would be preferred but my father and I have been drag racing for years so he might know how to cut in grind he did his rear end before I was even born haha. I am also upgrading the suspension all the way around and installing 4 wheel disc brakes so newer bigger tires are definitely on the list of to do's. Thanks for all of the help. Any other Suggestions?
 
Since you have a Duster, I would start looking for a 65-67 or 68-70 B body 8-3/4. Those rear ends are wider than the original A-body 8 3/4, but the Duster has much wider quarters than the Darts did anyway. The B-body 8 3/4's are cheaper, easier to find, and had the large bolt pattern from the factory. All they require for installation is relocating the spring perches, which is a pretty simple operation. While you're at it, you can set the perches up to use a 1/2" spring hanger/shackle offset from Dr. Diff, or a full 3" spring relocation so you can mini-tub the car for some really wide tires.

My Duster has a 68-70 B body 8 3/4, uses a 1/2" spring hanger/shackle offset (perches are 42" c-c now), and still has the stock wheel tubs. I run 18x10" rims with a 7" backspace and fit 295/35/18's on the car after a little quarter lip trimming.
 
I just put a strange 60 in my dart full bolt in 4 piston calipers slotted rotors 35 spline axles a little costly but worth every penny. There is also a picture of the 7 1/4 I took out of the car if yours looks like that you've got a 7 1/4
 

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Dart Swinger 72 said:
I just put a strange 60 in my dart full bolt in 4 piston calipers slotted rotors 35 spline axles a little costly but worth every penny. There is also a picture of the 7 1/4 I took out of the car if yours looks like that you've got a 7 1/4
Click to expand...

A "little costly" :D
 
SOME/many 7.25SGs have done pretty good behind teeners,automatics,stock rear suspensions and street tires.If you want to try it, pop the cover and check the cross-pin to case fit. If its tight, a fresh load of oil, and have a go. If I could I would try to decrease the side gear backlash.
But an 8.25 SG should take anything your teener can dish out. At least until you stroke it.They're cheap and plentiful, and well-supported as to parts.
 
Okay, I sure hope I put 400hp or I will be pissed haha. I will look for both a 8 3/4 and 8 1/4 and see what is readily available
 
Ya trailbeast I guess that was an understatement, but I have a friend who is a distributor for strange so I did get it for a little less than retail.
 
Ya trailbeast I guess that was a bit of an understatement, but I do have a friend who is a distributor for Strange so I got it for less than retail
 
Add me to the list of people who started with a 7 and 1/4 and blew it out the first weekend! It lasted about 3 burnouts (no hard launching) I thought the right rear tire would be the weak link..turns out I was the ring and pinion gear that smoked and tore up rather than the tire. I now have a Dana 60 with 3.54 gears (it cost me about $3500 plus about 200 in labor to have someone change the leaf spring u-bolts, and hook up the new drive shaft. Trust me....if you have the 7 1/4..you are about to knock over a stack of dominoes ($100 bills). IF your planning on making the engine stout, your gonna need something stout all the way back (solid trans, solid driveshaft, and solid rear end). Good luck! You said you are deployed, God bless you and your family and thank you for serving our country. Wish I could buy you lunch!
 
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