Which 8 3/4?

[73 Co challenger]

Is it possible to tell just what rear end housing this is just by looking at it? I know by the tag it has 3.23 gears

Also is it a posi if they both roll, one won't spin without the other?
1973 challenger

 

[DetMatt1]

There will be a 7 digit casting number on it. Both wheels will turn the same direction when you spin the yoke.

 

[Adam]

look on the lower left side, near the yoke. the last 3 digits will tell you what housing it is. look for orange paint around the fill plug.

 

[RzeroB]

look for orange paint around the fill plug.

interesting ... was that the assembly color code for a Sure-Grip to ensure the correct fluid was put in it?

 

[Adam]

I do not know if it was to ensure the correct oil or if it was simply for quick identification on the assembly line. In the attached pic the orange around the fill plug and across the bottom indicate a Sure Grip; the two blue and one white stripe indicate a 3.23 ratio; the yellow numbers are dates, I believe...

 

[70Hardtop]

That thing needs a serious clean first, before the pumpkin is popped. And to be able to read the casting numbers. It will most likely be a 742 case or a 489 case (last three digits). Mostly 69-72 years was 742 in passenger cars, 70-74 mostly 489, but transitions during the years. By 1973, all passenger cars had the 489 case (1 7/8 pinion diameter). Or that is what I read.

 

[moparleo]

Here are a few reference links that should help out.
Mopar Rear Ends / Differentials / Etc
I would recommend that you print this link and keep it for reference. A Lot of information.
http://www.wichitamopar.com/wp-content/uploads/2012/10/MOPAR-REAR-DIFFERENTIAL-INFORMATION.pdf