# Help locating posi/LSD rear end



## GroundHog (Oct 16, 2009)

I'm pretty good when it comes to the underhood stuff, but know absolutely jack s#@$ about rear ends. 

What I do know is that my 70 GTO has an open diff. I can always order an aftermarket LSD and put it in, but my question is what cars would have have come with posi that I potentially swap rear ends with? 

Also, what size gears would you recommend? It's mainly going to be driven around town, and I would like to have a little more low end torque as opposed to freeway cruising speed but I don't want to top out at 40 mph either.


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## Too Many Projects (Nov 15, 2008)

Any 68-72 GM A body axle will bolt in. I, personally, would shy away from any Olds axles, as they have a cone style posi and once worn out are not rebuildable. Chevs all had an Eaton rebuildable posi. I'm not familiar with what Buick used.
A 3.55 or 3.73 ratio will give a good low end boost without killing the engine on the freeway.


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## ppurfield001 (Jan 21, 2008)

Too Many Projects said:


> Any 68-72 GM A body axle will bolt in. I, personally, would shy away from any Olds axles, as they have a cone style posi and once worn out are not rebuildable. Chevs all had an Eaton rebuildable posi. I'm not familiar with what Buick used.
> A 3.55 or 3.73 ratio will give a good low end boost without killing the engine on the freeway.



:agree with Mitch. I went from 3.90:1 to 3:55:1 and its better all-around (reasonable balance between good torque and highway cruising). Good luck


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## geeteeohguy (Feb 2, 2008)

The Pontiac Safe-T-Track is also a cone unit like the Olds. They work well if not worn out or abused. The clutch type is better, though. I agree with the gears. For what you want, it sounds like a 3.55 would be about right. Easy gears to get, too. You do need to know what series carrier you have. If your rear is a 3.36, 3.55's will bolt right in. If you have a 3.23 or numerically lower, you'll need to change carriers, too.


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## GroundHog (Oct 16, 2009)

thanks for the info guys! looks like 3:55 gears sound right for me. 

another rookie question....how do i found out what series carrier i have?


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## geeteeohguy (Feb 2, 2008)

What gear ratio do you have now? 2-series carrier: 2.56-2.73; 3-series: 2.93---3.23; 4 series: 3.36--4.33.


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## GroundHog (Oct 16, 2009)

No idea what gears, but I counted the bolts as I was bleeding the brakes this weekend - 10 bolts. How can I tell what series carrier/gears I actually have in there?


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## Pontiac Tempest Cstm (Jun 18, 2008)

hey, im pretty sure you have to jack up the rear, put a chalk mark on the drive shaft then spin the wheel. howver many times the driveshaft spins while the tire makes one complete rotation is the gear set.once you know the gear you can fit what series it goes into.im sure some one else can varify if this is the correct way or not.good luck!


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## 68greengoat (Sep 15, 2005)

Close. For a non posi, you need to spin the wheel 2 times and count the rotations of the driveshaft.. 3 1/2 rotations would be a 3.55, and so on.... After reading this sticky, you will be well informed..........
http://www.gtoforum.com/f12/gto-gear-ratios-16289/


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## GroundHog (Oct 16, 2009)

awesome, thanks guys! i'll check that this weekend. 

you guys have been a great help!


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## Pontiac Tempest Cstm (Jun 18, 2008)

welcome ground hog and thans 68greengoat for correcting me


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