742 diff?

[chgr500]

Been lookin for a sure grip for my Charger for a while now....went to check one out today and may have one.....it is a 742 case where I have a 489 open legger......it's in a 70 Chrysler 300...big arse trailer hitch on it and has a rear sway bar set up.....I could only lift a single wheel off the ground due to it was parked too near the fence.....With the vehicle in nuetral and the park brake was released and not sticking...I couldn't turn the wheel....and could feel and see the axle moving the opposite tire so I figure it is a suregrip.....maybe a trailer tow package with that sway bar on it  they are to get the vehicle out and confirm with me at a later date.....seem to have quite a few mopars out there...most were for sale?
The 742 case should be O.K. .... looked like a smaller yoke than mine......car appears to have a 100k miles on it...still runs
Anything to watch for when I check the diff out next time....WIW?....thanks for your input

[John_Kunkel]

Sounds like it is a SG but expect the gear ratio to be 2.76 or 2.94 in that C barge.

[Chatt69chgr]

I got one of those for $100 out of a C-barge.  Now that was with a suregriip which was what I was after.  You can use the suregrip out of that 742 in your 489 case----just have to use the differential bearings that go with the 742.  And be careful not to lose the thrust bushings.  Lots of times they stick to the end of the axle when you pull it out.  The suregrips alone cost several hundred dollars new so let that be your guide as to what to pay.  The drag racers like the 742 case since it didn't use the crush sleeve.  But now you can get a solid spacer and shims for the 489 so you don't have to use the crush sleeve if you don't want to.  The 489 was std for the 69 and 70 chgrs.  The 742 may have come in the 68's.  I just don't know.  As John said, most likely the diff will be a 2.76 or 2.94 and I doubt you will want to run that ratio.
If you are going to use your 489 case then the yoke being different is moot.  There were four different flavors of yoke.  The 10 spline and 29 spline and the 2-1/8 inch and 2-5/8 inch.  But that suregrip should bolt right up to your ring gear assuming you are going to reuse it.  Be careful removing the suregrip from the ring gear.  Some of them use backwards thread bolts.  And if you are reusing them, don't mess them up as they cost a whole lot more than the clockwise threaded variety.  I believe Autozone has all the bearings you need.