irocarter

iTrader: (1)

I have a 10 bolt carrier and don't know if it's a seriesII or seriesIII. Is there away to measure it to find out. There is no ring gear on it. Thanks

sofakingdom

iTrader: (1)

No need to even measure... you can spot em from 100 yards away by eye.



2 series on the left. The difference is, how far the flange for the ring gear is located, away from the center of the pinion. Since "ratio" is NOT ONLY the ratio of the # of teeth on the 2 gears, BUT ALSO the ratio of their DIAMETER, then since the ring is always the same size for any given model of rear, as the ratio DECREASES, the pinion diameter INCREASES. Meaning, for a very low ratio, the pinion is very large, therefore the ring has to be located very far from its center. Now that you've thought through that, note how the ring flange on the carrier on the left is almost flat on the back, but the back side of it on the carrier on the right is visibly cone-shaped. THat's because in this model of rear, the difference in the flange placement is about 3/8".

irocarter

iTrader: (1)

Thanks Sofa. I had to read your post about 10x but I think I understand.
Just to make sure, If I had a seriesII and III sitting on a bench,with the ring gear side down on the bench,the seriesII ring gear flange would be closer to the bench?

sofakingdom

iTrader: (1)

Exactly.

About .375 - .400" closer to the bench than a 3 series would be.

Imagine taking the 2 units in the pic and setting them up on their bottom.

It's pretty straightforward actually. If you have a 2.73 R&P, then the pinion is 7.625" / 2.73 diameter, or about 2.8". Radius (distance from center to outer edge) is therefore about 1.4".

OTOH if you have a 3.73 gearset, then the pinion is 7.625" / 3.73 in diameter, or about 2.04", or about 1.02" radius. Approximately {drum roll please} .4" difference.

Therefore the ring has to be about .4" closer to the center of the pinion in the 3.73 than the 2.73, if all else is equal (which it isn't, but the point should be obvious). Thick gears are MUCH more expensive to make than thin ones. So if you imagine the factory starting out with the lowest possible # they could ever use, let's say 2.21 which would be 19 pinion teeth and 42 ring teeth, they'd make the ring as thin as possible and the teeth still stay stuck to it, and locate the carrier flange as far from the pinion as it needs to be. Then as progressively higher ratios were created, the pinion would get smaller and smaller, and the ring would get thicker and thicker so that it would still mesh with it, until at some point, the cost starts to rise steeply. At that point, they'd create a new carrier "series" by moving the flange over, and start over with the thinnest posssible ring. In the 7½" 10-bolt, that happens between 3.08 (13 & 40) and 3.23 (13 & 42). In some other models of rear especially ones used in trucks, there might be another step between a 3 series carrier and a 4 series.

Which is why the ring flange on that 2 series stock Auburn posi POS in my pic is nearly flat on the back, but the flange on the 3 series Auburn "hi perf" POS is cone shaped.

irocarter

iTrader: (1)

Thanks again Sofa. I believe I fully understand the difference of the two carriers now.
1 more question-factory gm carriers could possibly have had a 3.08 with either carrier?

sofakingdom

iTrader: (1)

No; that's 2 series. 3.23 is the lowest 3 series. (in this model of rear)

-=Z28=-

iTrader: (3)

Well put man! nice to read threads of such depth and knowledge!! What is your opinion on eaton vs auburn? I built my rear with auburn with 373 richmond gears. obviously new bearings and seals. kept stock axles. I dont plan on dragging the car. street only. but i have a 500hp 383... so far it has handled it. figure if Im not launching it...... Thanks again mang!

big gear head

The Auburn is junk, but if you treat it well it will last a long time. If you abuse it then you will be replacing it soon. Don't do any water burnouts or any burnouts while holding the brake.

Ron U.S.M.C.

big gear head ,
Can you get the steel clutch plates for the 7.5in Eaton Posi anymore or are they all carbon fiber ?

big gear head

I think the 7.5 clutches are smaller than the others. I have never replaced the clutches in one of them, so I can't say for sure. The 18 disc steel clutches are available for the 8.2 10 bolt and the 12 bolt.