what s the difference

[lee]

what is the difference between the 741 case and the 742 case on the 8 3/4 rearends can someone please tell me i want to put posi in my car and i want to know the difference before i go am start working on them

[Steve P.]

If your building a street car with a 3.73 or less the 741 case will be fine. If you are stepping up to a 4.10 or more gear for serious street and track time you will need to go to the 742 or 489 case.

There is more to it, but I can hardly see to type. Getting tired.  Dr. Diff has a great post on Moparts all about it. Sorry, no link..  I'm sure someone here has it..

[lee]

will the 742 case fit straight in with 323 gears with posi in the place of the 741 with no problem or will i have to change stuff

[Steve P.]

It will drop right in...    The 742 is THE case of choice. Strength and gear selection. It has it all..

[lee]

drop right in as in no changes like shorting the drive shaft or different splines just straight drop in

[Steve P.]

If you have a 741 now and are going to a 742 it will drop right in.

[Ghoste]

The only potential snag may be that the yokes are sized for different u-joints but you can get special ones to adapt from a change in size to whatever you need on the driveshaft.