How to identify 8 3/4 diff? 742 or 489

[Heimedw]

I'm going to have to do a pinion seal and don't know how to tell what 8 3/4 diff I have. The car is a 1964 if that helps. Thanks.

 

[kiwigtx]

Look for the casting number on the driver's side -





The last 3 digits are what you are looking at - the example above is a '741' head.

 

[moparsteve636]

The 741 is the smallest of the 8.75s, 1.3/8" pinion I believe the 742 is 1.75" and the 489 is the largest 1.7/8" Hope this helps!

 

[Heimedw]

Thanks very much. My first mopar.

 

[mopar12372]

a 741 is good and beefy compared to a gm 12 bolt , you can do burn outs doughnuts ect but if you have a 4 speed none of them will last .
nice i like it

 

[64BEL]

It's probably a 741 if it's the original for your '64.

 

[moparsteve636]

That will depend on the build date (early) as to if it has the 741 case