8 or 9 inch diff

[Smash It Up]

The diff on my car has a bulge ,slightly off centered,in the front facing part. Also the axles taper slightly about 2/3 of the way along toward the hub on each side. I read that this is the 9 inch?
Would this have been retrofitted or orignal to the car? I don't know if it would have been an option or not. Can I tell from the VIN ?
thanks

 

[zookeeper]

The quick and dirty way to tell a 9 from an 8 is to look at the bottom two bolts that hold the gear carrier in place. If you can get a socket on them, it's an 8 inch, if you have to use an end wrench, it's a 9 inch. Without knowing what year of car, what motor it came stock with, etc there's no way to know if it came stock in the car. The tapered axle housings don't really tell you much, since the stock 8 inch in my old '65 fastback had them as well.

 

[Smash It Up]

69 fastback 351w FMX auto. But isnt there a way to tell from the VIN or some other code that can tell me what it was meant to have originally?

 

[danny clemens]

If it's an original 351W (5th digit of the vin being an M or H) then it's a 9" that is if it's the original rear.

 

[Smash It Up]

Oh ok. Yeah it is an H code. Thanks for clearing that up !!