Difference between HO 33 and HO35 rear differential?

[mike16]

I am trying to buy a pinion seal for my truck
It is a 72 c10 longbed fleetside with a 307 and an SM 465.
It has coil rear suspension

Parts vendors ask me if it's an HO 33 or an HO 35.
What's the difference?
How can I determine which one I have so I can buy the correct pinion seal.

Thank you

[kwmech]

Are you sure its a rockwell rear and not a GM 12 bolt. Post up a picture of it if you can

[mike16]

Originally Posted by kwmech

Are you sure its a rockwell rear and not a GM 12 bolt. Post up a picture of it if you can

Not sure of anything. Hence the question .

It's got a 12 bolt inspection cover.

[SJLenz1340]

12 bolt refers to the number of bolts on the ring gear and has nothing to do with the cover.
There may be identifying numbers elsewhere on the rear end.

[MJN]

Originally Posted by SJLenz1340

12 bolt refers to the number of bolts on the ring gear and has nothing to do with the cover.
There may be identifying numbers elsewhere on the rear end.

This is incorrect- 12 bolt refers to the number of bolts holding the cover to the housing. While the 12 bolt does have 12 ring gear bolts, the 12 bolt reference is for the number of cover bolts. Same goes for when people refer to the GM 14 bolt- the number of bolts holding the cover to the housing. The 14-bolt uses 12 bolts on the ring gear but if you try to get parts for a 12 bolt and put them in a 14 bolt you'll be in for a surprise.

Per the GM parts book the pinion seal for a '72 C-10 is 3924031. This crosses to SKF 17190, National/Timken 8460N.

Your 72 should have a GM 12-bolt 8 7/8" ring gear axle.
https://static.summitracing.com/glob...gr-f890633.pdf

[mike16]

Originally Posted by MJN

This is incorrect- 12 bolt refers to the number of bolts holding the cover to the housing. While the 12 bolt does have 12 ring gear bolts, the 12 bolt reference is for the number of cover bolts. Same goes for when people refer to the GM 14 bolt- the number of bolts holding the cover to the housing. The 14-bolt uses 12 bolts on the ring gear but if you try to get parts for a 12 bolt and put them in a 14 bolt you'll be in for a surprise.

Per the GM parts book the pinion seal for a '72 C-10 is 3924031. This crosses to SKF 17190, National/Timken 8460N.

Your 72 should have a GM 12-bolt 8 7/8" ring gear axle.
https://static.summitracing.com/glob...gr-f890633.pdf

Thank you.