Can anyone please help me out and tell me what this posi unit I have is for? Its got some number on it and if ANYONE knows what they mean then let me know PLEASE!! it has #410409 N casted into it and has GM 12 under it. I am hoping "GM 12" means 12 bolt cause thats what Im looking for.

Brandon

I think that is a 8.5" 30 spline 10 bolt, 2 series. (2.41 and 2.56 gear ratios)
How many bolts do you count for the ring gear?

it's an 8.5 28 spline 2 series carrier.

There are 10 bolts on the carrier for the ring gear. I dont know much about diffs but I thought that meant 10 bolt, but just wasnt sure. Called some trans shops here locally and they all said they didnt know. How do you find this information out for future use. Like how do you decode these numbers? Now that I know what this is Im gonna list it on Ebay....thanks alot

Another question if someone could answer that would be awesome. the 12 bolt I have is from a 1964 El Camino, or so I was told. are 12 bolt 30 spline standard or are there some that are 28? Or should I just stop being lazy and pull an axle out?

All Chevy car 12 bolt rear ends had 30 spline axles. This will not be a '64 rear end because the first year for the 12 bolt was '65. I agree that the 410409 is the 2 series 28 spline Traction Lock for the 8.5 10 bolt. The 3 series is 410408. The 3 series accepts gears from 2.73 to 5.13.

Well, there you have it. Sorry I was wrong on the spline count though. I figured it was a 2 series 10 bolt but said it was 30 spline. If Freddie says it is a 28,.....it is a 28.

Awesome thanks alot guys. this really helps. Is there any way I could learn these numbers? Is there a book or web site. I seem to run on to alot of these that seems to be a mystery. Thanks again.

Just Google 410409N and see what you get.
Look here..... http://www.wallaceracing.com/carrier-id.html

Now you know the two for the 8.5. The 12 bolt is ED32088 for the 2 series, EDB30140 for the 3 series and EDB30174 for the 4 series. The 8.2 10 bolt is ED32118 for the 2 series and EDB30116 for the 3 series. The 12 bolt and 8.2 will be Eaton. That should be all you need to know.

Awesome Thanks