68 RoadRunner vs. 73 Duster?????

[IceMans68RdRunner]

How much lighter is my Duster then the RoadRunner I drag race. They are both all stock. Both have 440s in them. And one other thing, how do you make sure that you have an 8 3/4 rear end???? I bought the Duster just recently and the person said it has any 8 3/4 rear end, I measured it drum to drum and it is 4 inches shorter then the 8 3/4 in the RoadRunner, is this common. Are the Third members enterchangeable in all rearends???? The casing on the RoadRunner is a 742 and the casing on the Duster is a 742 also.

All the info. is greatly appreciated!!!

Thanks,

Bryan

[aspen78]

Unless I am mistaken iceman, all 8 3/4 rear ends are interchangable, so long as the casting # on the carrier is the same if both are 742 you should be able to swap them. To tell an 8 3/4 is easy, look at the diff from behind the car, if you do not see any bolts the odds are good that it is the real deal. The carrier unbolts at the front, and pulls out, but the axles need to be slid out, (how much and how to do it i am not sure) I have seen guys swap carriers in 20 minutes at the racetrack, but I am sure they have done it before.-------oh yea by interchangeable, I mean the carrier, not the whole rear-end. Hope this helps, as for weight I would think your runner is heavier, but drive it to a self-weigh scale and you can find out for sure.

[66Dodge]

When reference is made to 8 3/4 rear end, what we talk about is the type of differential housing.
Any Mopar can have one but depending on the body style A,B,C, or E the total width of the entire axle housing will differ. Hence, the 4 inches difference between the Duster and the RR.

BTW, the RR is quite heavier than a Duster.

[PRO]

All 8.75 carriers are interchangeble(except 1958-59 which have a different bolt pattern)as all use the same amount of axle splines,your only real difference is if you have a big u joint or small u joint style yoke,this is an easy fix as you can buy a conversion u joint at napa.The 742 carrier has a 1.75 straight pinion gear,the 489 has a 1.875 tapered pinion gear and the 741 has a 1.375 straight pinion gear,Ive listed them in order of overall strength.My 73 BB duster weighed 3300 lbs partially gutted and my 68 BB sport sattelite weighed 3675 lbs in full trim(eventually weighed 3250 gutted) but I imagine your roadburner is closer to 3750............PRO....

[IceMans68RdRunner]

Thanks You all for the replies!!!! So if I dont see any bolts on the back side of the rear end, then it is an 8 3/4. That is exactly how the Dusters rear end looks. I wasnt sure about the overall lengh from drum to drum thats why I asked, but since you all said it is common that all cars not be the same width then that makes me feel a little better. Do you think the stock axles will hold up ok????

Thanks again,

Bryan

[amoparguy]

There is also a couple of different u-joint sizes. If you are getting an extra centersection to swap, measure the width of the cross to make sure it has the same size joints. For more info you can check this link...


http://www.geocities.com/musclemopars/moparrearaxle.htm

[IceMans68RdRunner]

Thanks for the info. So a stock Duster weights about 400 pounds lighter than a stock RoadRunner. Geez I didnt think it was that much, but it will be a good thing.

Thanks,

Bryan