Dana or 8.75 question

Engine, Trans & Driveline

  1. plumcrzy90

    plumcrzy90 Member

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    I have a 1969 road runner that currently has a 7 1/4 in it and I know that won't work but I do have an extra 8 3/4 that came with the car but I don't know what to do to it so it can handle the ranges of 450 to 500 horsepower or should I just go dana? Any advice would be appreciated.
     
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    • flypaper

      flypaper FBBO Gold Member FBBO Gold Member

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      A 8 3/4 will hold up just fine.
       
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      • WileERobby

        WileERobby Well-Known Member

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        It will handle that horsepower just fine. No need for a Dana.
         
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        • plumcrzy90

          plumcrzy90 Member

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          Do I need to add a sure grip to it or will the open work? I want to change the gearing because the 2.76 will be too high for me.
           
        • WileERobby

          WileERobby Well-Known Member

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          The open will "work", you'll just burn rubber on one tire
           
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          • plumcrzy90

            plumcrzy90 Member

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            Alright thanks guys! I will go back to Dr diff and do some more research. With this new info I can get by way cheaper!
             
          • HEMI-ITIS

            HEMI-ITIS STREETER

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            Make sure the assembly is done right the 1st time!
             
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            • WileERobby

              WileERobby Well-Known Member

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              I'd get the sure grip diff.
               
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              • ocdart

                ocdart FBBO Gold Member FBBO Gold Member

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                I'd be curious where the 7-1/4 came from and why. Certainly not from the factory in a Roadrunner.
                Either the rear end was put in to replace an 8-3/4 for some strange reason or the car isn't a real Roadrunner. Have you verified the VIN - or looked to make sure all of the stamped VINs are identical?
                 
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                • plumcrzy90

                  plumcrzy90 Member

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                  The 7 1/4 was just what was laying around to replace a missing rear. I think it's from a 68 satellite. But yes all the body numbers match just not the engine and trans of course.
                   
                • MoparLeo

                  MoparLeo NRA PATRON LEVEL LIFE MEMBER

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                  Did you just happen upon a 450-500 hp engine for this car ? There seems to be either a lot of info missing or this is a funny.? What exactly do you have ? Engine size/combo ? Actual dyno numbers for HP and Torque and at what rpms ? Not wishful guesses. Trans type/gearing ? Suspension type/mods ? Tire/wheel sizes ? Differential type and gear ratio ? What is actually in this car ?
                   
                • 69roadr

                  69roadr FBBO Gold Member FBBO Gold Member

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                  With 450 to 500 horsepower you're going to need a sure grip I got one in my roadrunner and it burns rubber like crazy
                   
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                  • 66Satellite47

                    66Satellite47 FBBO Gold Member FBBO Gold Member

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                    Just my opinion, seems like an 8 3/4 can easily handle up to 500 HP, properly set up. With my drag cars, went to the Dana 60. My 1st drag car with 8 3/4 didn't hold up that well with 450-500 HP, but had several issues with that one. As a 4 spd it also twisted one 8 3/4 axle. Dana's don't break, but 8 3/4 can do just fine until you get LOTS of power & traction. Limited slip is required for a performance application.
                     
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                    • 91r/t

                      91r/t FBBO Gold Member FBBO Gold Member

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                      A one wheel peel will be mildly insane in that car with 500HP. Trust me I had my sure grip die in my Charger with 500+ HP and it was a handful without any traction what so ever haha! It's bad enough with a sure grip and street rubber, let alone a one wheel peel. Sure grip and an 8 3/4 will be fine. The biggest problem is when you start running slicks and launching at the drag strip. Thats extremely hard on parts and when you start breaking stuff. Just a street burnout or moving tire spin with street tires and minimal traction, and you'll be fine with the 8 3/4 for your value and even more HP. Remember......traction breaks more parts not necessarily just horsepower.
                      :thumbsup:
                       
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                      • zyzzyx

                        zyzzyx FBBO Gold Member FBBO Gold Member

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                        The Reason Ma Mopar started to put Dana's in these cars is NOT the horsepower figures, it's the 4-speed cars
                        constant shock! An 8-3/4 will take the horsepower and torque if it's behind and automatic, but if you are going to
                        race this thing with a 4-speed then you need a Dana, and a posi, or even a spool!
                         
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                        • beanhead

                          beanhead FBBO Gold Member FBBO Gold Member

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                          8-3/4 more than adequate. As the guys above have stated, a limited-slip differential is a must on anything with some power in my opinion..the thing to check is, your 3rd member's casting number. Hopefully it ends in '489' (very outside chance it could be a '742') but if it's the '741' unit it had the smaller yoke..check that and then look for the proper rebuild kit (bearings,seals,etc..) New gears and a new differential unit and you're ready to smoke 'em. OK more of my feeble opinion here: Depending on your budget..have it built professionally unless you know what you're doing and have the tools. The (Eaton) True-Trac differentials are superior to the factory clutch or cone style units, especially with the quality of parts nowadays...I have a really good rear-end shop locally but if you're not sure about that, Dr.Diff is an excellent place to start--you're on the right track!
                           
                        • 5.7 hemi

                          5.7 hemi FBBO Gold Member FBBO Gold Member

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                          Dr. Diff has a new Eaton style True Trac, prices at 450! If I had an 8 3/4, I’d get that.
                           
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                          • 66Satellite47

                            66Satellite47 FBBO Gold Member FBBO Gold Member

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                            I still remain a 742 fan. Easier to rebuild in my opinion. Shims seem better to me than the crush sleeve. 8 3/4 is great for any street sort of car without GREAT traction. Big tork & traction go for the Dana. 60's are heavy but are tough.
                             
                          • 5.7 hemi

                            5.7 hemi FBBO Gold Member FBBO Gold Member

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                            Use the crush sleeve eliminator kit on the 489, done!
                             
                          • 66Satellite47

                            66Satellite47 FBBO Gold Member FBBO Gold Member

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                            Very true. But I won't worry, my Satellite already has the Dana.
                             
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