Is my rear end strong enough

Big Block A body Tech

  1. Resto

    Resto Well-Known Member

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    Hey,, I'm restoring a 74 Dart swinger. I pulled out the original /6 and 904 and I'm:sign3: wanting to put in either a 383 or 440.. Will my 8 1/4 rear end be strong enough or will I need an 8 3/4 rear.. Thanks
     
  2. 68gtxman

    68gtxman I used to reMember

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    Doing a lot of burn outs? Going drag racing? If so, then upgrade. If not, then use what you got.

    You could always just upgrade after you break it.
     
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    • Leadfoot

      Leadfoot Jane Goodall of the N&P Forum

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      They're stronger than a 741. At least they have a larger pinion shaft. It doesn't mean they're stronger but they should at least be comparable. Gears matter. The lower the gears, the less stress they are subject to. What tires?? Slicks at the track or street tires on the street? Last is the engine and drive train. A stock engine converter doesn't hit near as hard as a built engine with a higher stall converter.
      Sorry if I haven't been any help.

      Personally, I think they're plenty strong and will more than hold up. If I'm wrong the worst you have to do is replace it. Which is what you need to do anyways if it's deemed to be too weak.
       
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      • younggun2.0

        younggun2.0 Well-Known Member

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        run it until you get the new combo all worked out and tuned well. when it starts making power and running well the weak links start showing up. if you start replacing parts that will work with parts that are meant for future plans you will have a car that is apart alot longer and cost alot more. i did exactly that and it took me 10yrs to get my car back on the street.
         
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        • d5667

          d5667 Member this?

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          Sure no problem just make sure your Nike's are in good shape
           
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          • RustyRatRod

            RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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            BS on upgrading. I have a friend who has a Demon that had an 8 1/4 in it. Car ran 11s yankin the wheels leavin. He upgraded to an 8 3/4 but not because he broke anything. He was upgrading the whole car. He still has the 8 1/4. They are plenty strong.
             
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            • 72ScampTramp

              72ScampTramp Scamp Tramp

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              Talk to wormanator. He has a BB duster running 11s with a 8 1/4.
               
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              • swinger340

                swinger340 Well-Known Member

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                Have seen a 72 4 speed roadrunner and a 1/2 ton pick up both with 440s and a 72 swinger with a built up 360 take poundings and do lots of burnouts w 8 1/4s for yrs w/o blowing up. Id run what you got.
                 
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                • Woods74

                  Woods74 Broke Senior

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                  Look into the 8.8 swap too. It's one of the top sticky's in transmission/drivetrain.
                   
                • RustyRatRod

                  RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                  The 8 1/4 (actually 8 3/8) pinion diameter is 1.625. That's 1 5/8 for the decimal impaired. The GM 12 bolt pinion diameter is........wait for it.........1.625. I've seen 12 bolts take in excess if 1000HP. Course they had good stuff in them. I'll be damned If I would swap in some inferior phord crappola when what you have will work just fine.
                   
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                  • 66dartman

                    66dartman Well-Known Member

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                    Only thing is those pesky c-clips.... Sure is easier to set one up than a dana, like those adjustable carrier bearing spanners. Should hold up until you break an axle.
                     
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                    • moper

                      moper FABO Gold Member FABO Gold Member

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                      It's not usually the pinions that shear. It's ususally the caps that flex and move. The 81/4 is a decent rear. If it has the gearing and differntial you want I'd leave it and if it breaks, upgrade. If you have to go through it, re-gear, or add a limited slip unit - just upgrade now. I wouldn't spend much on it.
                       
                    • RustyRatRod

                      RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                      I've seen that arguement before too. But in all my years around cars, I have seen precious few c clip buttons broken. They don't hold a load at all. They simply keep the axle in place. It's a good rear end.

                      I've actually been looking for one for a long time to trade for my complete 8 3/4 sure grip under my 63 Dart, but no one's ever come through. I guess my little slant car will just have overkill, and that's fine too. lol
                       
                    • Oldmanmopar

                      Oldmanmopar Going left turning right FABO Gold Member

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                      Only someone standing close to you could answer this question. Or you could sit in a bath tub and smell the bubbles.
                       
                    • metallidart

                      metallidart member me?

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                      I'm going to go through mine, add a sure-grip, and hope it lasts for a little while behind my 422. I won't be running sticky tires though.
                       
                    • rnaz

                      rnaz nitrous fed 390

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                      I agree. I put well over 450hp through an 8-1/4 in a 4800lb truck and ran 12's all day long for years in it. The trans lost 2nd gear before the rear end even blinked at the power.
                       
                    • Resto

                      Resto Well-Known Member

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                      Awesome. I bought this car I'm restoring completely disassembled. Rear end as well. I was curious if I need to look for another one. Thank you guys for all the good answers. I'm going to stick with 8 1/4.
                       
                    • wanta68cuda

                      wanta68cuda Well-Known Member

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                      Dang!!! Where were you four month's ago when I was trying to sell or trade my 8 1/4 sure grip!!! That's always my luck. LOL:banghead:
                       
                    • Steve Reynolds

                      Steve Reynolds Member

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                      We drag race a 71 Demon, 440 rb 727 & 8 3/4, 4.30 gear, runs low 10's on foot brake. Broke 2 ring and pinions and cases (489) and 1 sprag. Going to a dana cause I put in a trans brake, don't want to take any more chances.
                      Steve
                       
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                      • RustyRatRod

                        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                        If you didn't put a crush sleeve eliminator in that 489, there's your reason. 489s with crush sleeves and 742s usually hold up at those ETs.
                         
                      • inkjunkie

                        inkjunkie Well-Known Member

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                        Or just cup your butt, let one rip and smell your hand......just in case you do not have a tub in your house....
                         
                      • Steve Reynolds

                        Steve Reynolds Member

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                        Crush sleeve eliminator was in both 489 cases, the main cap on right side broke both times, but after 400 + runs & more the ring & pinion & the case said enough.
                        Steve
                         
                      • womanator

                        womanator Well-Known Member

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                        74 Duster full interior.
                        We call it the trainer car because you have to learn how to cut lights before you get in one of the faster cars.

                        8 1/4 rearend with 3.91 gears and sure grip.
                        Smog engine with a few up grades.
                        Runs 12.21 off the juice and 11.59 with 100 hp of juice.
                        Well over 300 pass's with the 8 1/4.
                        Waiting for it to brake.
                        Road hard and put away wet.
                        3200 lb car.

                        Trainee Jon.
                        [​IMG]

                        [​IMG]

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