I have a question. I was wondering if anybody could answer it for me. What is the difference between a 10 bolt Posi 2 series and a 10 bolt Posi 3 series carrier? Is it the gear ratio that they will accept and if so what are the gear ratios they will accpet.

Your pretty much right 2 series are for the gears in the 2:00-2:73 to 1 range, and the three series are for the 3:08 to 1 and numerically higher range. But you can buy a ring gear spacer to use a 2 series with a 3:08 and up gear.

The ring gear for a three series carrier will be thinner than a ring gear for a two series carrier, The carrier lip that the ring gear mounts up to is thicker on a three series carrier.

Thanks Guys. That is what I need to know. Is there any problem with a 2 series on a mild street car?

The series depends on which rear end you have. The 8.2 10 bolt and 12 bolt use a 3 series for 3.08-3.73 gears, the 8.5 10 bolt uses a 3 series for 2.73-5.56 gears, the 8.2 BP and 8.5 "O" uses a 3 series for 3.23-4.XX gears and so on. Some rear ends only have one differential for all gear ratios.

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'69 RS/SS396 Pro Street
427 4 speed 9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead (http://www.lubedealer.com/biggearhead)

big gear head - How do you tell the difference between the different 10 bolts? Mine is an original 10 bolt in a 79 Z-28 with 3.73 gearing. It is a non-posi and I am looking to buy a used posi unit.

2 series posi carrier casting# ends in 409; 3 series ends in 408.

If you have a '79 with the original rear end then it is a 8.5 10 bolt. The 8.5 has a 1 1/4 pinion nut and 7/16 ring gear bolts with 3/4 heads and left hand threads. The 8.2 10 bolt has a 1 1/8 pinion nut and 3/8 ring gear bolts with 9/16 heads.

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'69 RS/SS396 Pro Street
427 4 speed 9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead (http://www.lubedealer.com/biggearhead)

So my 79 would have a 8.5, (3.73) 3 series and to use a 2 series carrier I would have to use the spacer ring. Are there any company's that make a thicker ring gear to compensate for the spacer ring? Also is a 2 series carrier considered to be weaker than a 3 series?

Also, if you might know, what would be the axle spline count on a non-posi 3 series out of my 79 Z-28 Camaro?

<font face="Arial,Verdana" size="2">Originally posted by MPH:
Are there any company's that make a thicker ring gear to compensate for the spacer ring? </font>

I have heard of 4th gen (7.5") guys doing so, so I would assume that they are out there for the 8.5" as well.

<font face="Arial,Verdana" size="2">Originally posted by WildBillyT:
I have heard of 4th gen (7.5") guys doing so, so I would assume that they are out there for the 8.5" as well.</font>

You'd think so, but I've never seen them. They are available for the 12 bolts, but not for much greater #'s of 8.5's in the field. http://www.nastyz28.com/ubb/frown.gif

There are no thick gears for the 8.5 10 bolt. The 2 series and 3 series are the same as far as strength. You make the 2 series weaker when you use a spacer. All 8.5 F body rear ends have 28 spline axles unless someone has upgraded to 30 spline axles.

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'69 RS/SS396 Pro Street
427 4 speed 9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead (http://www.lubedealer.com/biggearhead)