Rear End Case Stamping Numbers and is it a Sure Grip on my 70 RR?

Fairly new owner of a 70 RR. Looked at the casting numbers on the rear end case today; Numbers are
4
2881489
9

Means I have a 489 type rear case. What does the 4 and the 9 mean? And the 9 has 3 small 000's under it. (The rear end has a 3:91 gear in it now)
Not sure about if it is a Sure Grip or not......when I turn the right side rear wheel the left side rear wheel turns in the same direction......

thanks

It may very well be a SG since both wheels go in the same direction....now lower one wheel to the ground and see how much force you have to apply to the other wheel. If you can hardly rotate it or can't, most likely it has a SG in there. Next, take the car out and see how long it'll lay down two black marks! Numbers on the case doesn't tell you what's in it but putting one wheel on the ground will let you know if it's in good shape or not. Just make sure the fronts are blocked.

Found this Mopar Sure Grip web site http://www.mopar1.us/axle/sm03b.html

Looks like I got a Sure Grip

SURE-GRIP DIFFERENTIAL IDENTIFICATION (back to CONTENTS)

Identification of Sure-Grip differential assembly can easily be made by lifting both rear wheels off the ground and turning them. If both rear wheels turn in the same direction simultaneously, the vehicle is equipped with a Sure-Grip Differential. Another means of identification is by removing the filler plug and using a flashlight to look through the filler plug hole to identify the type of differential case.

That last post quote wont work for an 8 3/4!

Don't understand......when I spin one rear wheel the other spins in the same direction and I have 8 3/4 rear end.......please explain?

thanks

5.7 hemi said:

That last post quote wont work for an 8 3/4!

Click to expand...

Years back I was faked out by a car in a wrecking yard when both wheels turned in the same direction and after pulling the pig out, it was an open unit but was rusty and the spiders were pretty much locked up making both wheels turn together. That's why I said to put one wheel on the ground now and see how much effort it takes to turn the other one. If it's in good shape, it should be difficult at least. As for looking into the fill plug.....you will get a good view of the pinion gear but if you try and look in at an angle, you might get a glimpse of the SG unit but it wont' be easy to get that look and try to shine a light in there too. The pic in the link you posted shows a cone style unit. The clutch style will have a square shoulder instead of a rounded one. There's lots of pics on the net showing what each looks like so familiarize yourself and just maybe you can look in and tell.....but getting out and doing a burnout will also tell you

burnout lets see it!!!!!