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Dana or 8.75 question

plumcrzy90

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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.
 
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.
 
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!
 
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?
 
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.
 
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 ?
 
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
 
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.
 
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:
 
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!
 
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!
 
Dr. Diff has a new Eaton style True Trac, prices at 450! If I had an 8 3/4, I’d get that.
 
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.
 
Use the crush sleeve eliminator kit on the 489, done!
 
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