I have a "2 series" 9 bolt posi carrier that was removed from a 1LE. As I shop for gears I see that some specify if you have a 2 series or a 3 series carrier.

What is the difference and why wouldnt they be interchangeable? What makes them so different? The person I purchased it from swears the rear end was a 2.77 but I am not sure if I believe him or not.

Regardless I am just trying to find out as I want to run in the ballpark of a 3.42.

Thanks!

 

Think about the definition of gear ratio for a minute. It means the number of teeth on the one, divided by the number of teeth on the other, right? Well, there's more to it than that.... it's also the ratio of the diameter of the ring, to the diameter of the pinion..

In a given model of rear end, such as the 7½", the ring gear is always the same diameter (in this case, 7.5") regardless of the ratio. That means that the pinion gear diameter changes, in exact proportion to the changes in ratio. In other words, a 3.73 pinion gear is 1/3.73 the diameter of the ring; but a 2.77 pinion is 1/2.77 of the diameter of the ring...... i.e., considereably larger. Which means, that since the place on the carrier that the ring mounts to is fixed, as the ratio increases, the diameter of the pinion decreases; so the thickness of the ring must increase, to move the teeth over toward the (smaller) pinion.

It's expensive to make real thick ring gears. So what the factories all do, is to break the range of ratios down at some convenient point; and make carriers in steps, with their ring flanges at different distances from the pinion center. In the case of the 9-bolt, the break occurs between 3.08 and 3.27; i.e. 3.08 and down have a 2-series carrier, with the flange relatively far away from the pinion center; and 3.27 and up are mounted on a 3 series carrier, with the flange closer to the pinion center, so that the ring doesn't have to be so thick.

You can mount 3 series gears on a 2 series carrier, by using either "special" thick gears, or a spacer; but there's no way to mount 2 series gears on a 3 series carrier, unless you can find a spacer that makes things thinner instead of thicker.

Here's a pic of a 2 series and a 3 series carrier side by side. These are 7.5" 10-bolt ones, but the principle is similar for all makes and models of differentials. Note how the 2 series one on the left has the flange closer to the bearing that's below it, and so the back side looks flat; where the 3 series one on the right has the flange moved visibly toward the center, and the back side of the flange is more cone-shaped.

It makes no difference that the car it came from had the 1LE option.

 

That is an excellent description on the difference and the images paint the picture.

Thank you very much for clarifying and identifying the differences. I greatly appreciate your input!

 

is there a part # difference between the carriers ? I still can't tell looking at a rear I just picked up, vs your pictures.. It's out of a '91 camaro, it's an auburn and has GM 3.73 gears. I can't tell if the GM gears are the big type for a series 2, or if the carrier + gears are series 3..

 

Fast look on the ring gear the ratio should be stamped on it.

 

I know that, it is 3.73. But I was trying to figure out if it was a 3.73 gear set for a series 2 carrier, or series 3..

I ended up mesuring them compared to my richmonds and have determined it's series 3.

Now I need to figure out if its an auburn pro carrier, or just a auburn GM oem carrier.

-- Joe

 

When I checked between the 2 carriers( 10 bolt) therewas about 0.25"difference between the 2 ( depth of the mounting surface for the gear).

 

That will be true for different size ring gears, but a ring gear in 3.73 should be WAY thicker for a series 2 carrier than a 3.73 for a series 3.

-- Joe

 

for sure it would . . Because the mounting flange on the series 2 carrier would be receased more ( more room). either that or I have it exactely backwards

 

My car has a differential that looks like the one on the left, does that mean I have a 2 series posi? So that would mean I have a 3.23 or taller gears? I was told it was a 3.42.

Also, what do those extra springs in the diff on the right do?

 

engage the LSD

 

So mine is not a posi then?