8 3/4 diff case

[Rog]

I found 3 differential cases, all sure grips (no ring gears) for $200 each. The seller doesn't know what carrier they came out of. If there is a cone type in the bunch I know its from a 489 carrier. Is there any way to know if a clutch type came from a 741 or742? I have a 742 and a 489 carrier so my bases are covered, however I have heard that in order to use a earlier diff in a 489 case you have to retain the bearings? Why? Can someone help me out? Thanks Roger

[Chuck'64]

The sure grip will work in any 8 3/4 housing so long as you use the bearings for that case (i.e. 741 sure grip with 489 bearings will fit in 489 housing)
Chuck

[6 packin]

All the sure grips are interchangable! The diff in them is the pinion size! I think like this off top of my head! 741 case small pinion(1 3/8, 742 large pinion 1 3/4, 489 tappered pinion 1 7/8. All can be known by lookin at the pinion! As for the strengh I have a friend that has abou 600 HP and 200 shot on NOS and uses the small 741 case for years with NO failures! Try to get the old style sure grips Pre 1970 I belive! There rebuildable!

[amoparman]

If your talking about third members then yes they all will bolt in to any 8 3/4 axle housing. If you are just talking about the posi units themselves they can be interchanged provided you use the carrier bearing the unit came out of. Example: to use a posi unit out of a 742 case in a 489 case you need to use 742 carrier bearings. This is due to different bearing ID on the 742 (smaller) to acommodate the 742 carrier size. The OD of the bearing is the same between the two cases, so the housing and the bearing caps are fine. Obviously all the other bearings are specific to the case ( inner and outer pinion). I just did this swap on mine.

[gsmopar]

Hey, I need one of those 742 cases. Would you like to sell me one? I'll pay shipping.

Thanks,

Greg

aultlt1@cox.net

[Rog]

It seems that the terminology used when talking about rearends confuses us sometimes. What I wanted to know is the interchangability of the diff cases (the unit that houses the clutches/cones, ring gear and recieves the axles), with either the 741, 742 and 489 carriers (the unit that holds the diff case then, as an assy goes in the front of the rearend housing. I think I have 2 contradicting answers here unless both are saying the same thing and I'm not getting it. I'm thinking use the bearings for the specific differential case since Amoparman just made this swap. Once all the smoke clears and I decide whats going in the coupe I will probably keep the rest of the stuff and set em up with different ratios or just spares. Thanks for the help. Roger

[Dart]

I think the problems lies in the terminology...

Are you referring to the axle HOUSING? I.E. the axle tubes, inner axle shafts, inner shaft bearings, backing plates etc?

The case would be the center section, AKA the Third Member (741, 742, 489).

All of the inner axle shafts, bearings, backing plates etc. are interchangeable between HOUSINGS. The Center Section or case is also interchangeable between housings. The individual parts in the cases will interchange as mentioned previously.

Obvioulsy this covers '65-74 8 3/4's. The earlier ones have the large nut on the drum.