[92GTA]

So my rear axle housing code says that I should have 3.23 rear end gears.

When I am cruising down the highway about about 71mph, the engine RPM is right at 3,000. I have a TH400.

Does that sound about right? I not used to non-OD autos to know if that's about right.

Thanks!

[Steve C.]

Check for the calculator here:

http://www.wallaceracing.com/Calculators.htm


.

[b-man]

Pretty much on the money for a 3.23 gear and a 26" or 27" tire.

Had a Doug Nash 5-speed (1:1 fifth gear) and a 3.25 geared Ford 9-inch many years ago, it ran right at 3000 RPM at 70 MPH with a 235/60-15 tire.

[72projectbird]

Yup, sounds right.

I have a TH350, 3.23's, and a 255/60-15 rear tire and I'm right around 2,800 @ 70Mph.

[92GTA]

Yeah I have 245/60-14. Ok cool, good to know the factory rear end hasn't been messed with.

From what I find find tho on BOP rear ends, if I want a posi I need to swap to 3.36 gears. If that right?

[b-man]

Originally Posted by 92GTA

Yeah I have 245/60-14. Ok cool, good to know the factory rear end hasn't been messed with.

From what I find find tho on BOP rear ends, if I want a posi I need to swap to 3.36 gears. If that right?

The aftermarket 8.2' posi units (which are far superior to the factory units) are 4-series, only made to fit 3.36 and higher gears numerically. If you're wanting to keep the 3.23 hears you'll have to source a used factory 3-series unit that only accepts 2.93, 3.08 and 3.23 gears.

My advice would be to ditch the factory 8.2" 10-bolt and upgrade to a corporate 8.5" 10-bolt (from a Nova or other X-body clone) or a Chevy 12-bolt before throwing money at the weak 8.2" rear.

The benefits are huge, far better gear selection and posi unit choices not to mention probably the biggest benefit, superior strength.

[johnta1]

You need the tire diameter also.

Here's a link to a calculator:

Calc Gear

[AJD1964]

Not sure what car you have but this may be an option:

Auburn Gear 5420114
HP Differential
1964-71 Buick, Oldsmobile, Pontiac (Non "C" Lock)
10-Bolt, 28-Spline
Ratio: 2.93 to 3.23

[92GTA]

That looks like a really good option, only $413 on Summit! I can't afford to replace my rear end for a stronger one anytime soon but I wouldn't mind throwing that at it to get rid of my one legger.

Thanks!

Which of these install kits would be the minimum I need to install that Auburn posi?

http://www.ronsmachiningservice.net/gm-8-2-bop-1/

[AJD1964]

Originally Posted by 92GTA

Which of these install kits would be the minimum I need to install that Auburn posi?

The Auburn unit includes new carrier bearings and the friction modifier fluid. I would talk to your installer/tech about any extras. I do not have it in yet.

I went with the Auburn, because I wanted to stay with a real nice '69 3.23 open complete axle housing assembly I came across. I'm just gonna switch carriers, and swap the whole thing into my '71.

I also have an Auburn in my '64 GTO with 3.55's. I'ts been excellent since 2004, but I do NOT seriously race it, nor do I have sticky tires. If you are going to do any racing or using sticky tires, b-man's advice is better. I hear the Eaton units might be better, in respect to racing applications and/or rebuilding options.

[92GTA]

Gotcha, thanks.

I'll ask my transmission guy, I'm going to have him do a TransGo re-calibration kit in my TH400 and I'd love to go posi at the same time.

No serious racing or drag radials for another year and when I do I'll store the numbers matching rear and run an aftermarket unit.

[68 Firebird]

In my cruiser I went with the Auburn HP posi unit to reuse my original 3:08 gears.
Been very happy with it. Also have a mild street/strip retune on my th400 wit a 13" Continental Converter. Docile around town but get on it and she will do quite well.

Gerry

[MD79TA]

Originally Posted by 92GTA

Yeah I have 245/60-14. Ok cool, good to know the factory rear end hasn't been messed with.

From what I find find tho on BOP rear ends, if I want a posi I need to swap to 3.36 gears. If that right?

Sent you a pm . Hsve a 2.93 peg leg and you have options. No reason to upgrade if your not racing and using sticky tires. The 8.2 rear end is fine for the the stock hp and torque and average driver. Doug

[92GTA]

Yeah I found a Yukon on Summit for $105, super tempting...