[big matt]

Morning all. My 70 has factory 3.73 gears in the 12 bolt but it also is a open diff. I am looking to see if i can retain my gear set, unbolt my ring gear and just install a lsd. Any opinions offered on what i can do here would be great. If someone even has a oem unit i can buy, pm me. Thanks

[Jack Ferris]

Easily done. Check backlash with a dial indicator before hand. Adjust side shims if needed with the new carrier to get the backlash the same as it was. Check lash in 3 places, like in a triangle to make sure ring gear is flat on new carrier.

[skunkwerks]

Yes you can retain your gear set. Try to get an original Eaton 12 bolt carrier and rebuild it if needed with new posi-clutch kit and bearings. Doing this will help keep your pinion depth shim adjustments to a minimum ( or no adjustment) and your side loading shims for back lash should stay the same. Open carriers are the same dimensions as a limited slip carrier. Aftermarket carriers are made close to the same dimensions as factory but are not close to the original GM tolerances. I have found you will have to adjust pinion shims and side load to re-setup the gears correctly.

[big matt]

Thanks. Any suggestions on an aftermarket unit or the best place to find a used oem unit?

[Formulabruce]

A "offshore" brand "posi" or Limited slip ( under $300 bucks) will probably have carbon fiber "clutches", the Real Deal Eaton ( $ 500-650) will have Steel, and will need Less shims and fit better I have found, as I have used Both.
However, you can do this WITHOUT removing your carrier. A Powertrax Locking ( and unlocking) unit will FIT right in your carrier while its in the car. There are instructions for installation right on the site.
https://www.powertrax.com/traction-s...nesize%3A_ANY_
Link to one on Ebay , its the correct 30 spline unit http://www.ebay.com/itm/PowerTrax-19...BXPM8g&vxp=mtr

[big matt]

Thank you Bruce. That looks like the ticket. I will do some more reading on it.

[Butcher]

Big Matt,
If you look on the Cleveland Craig's list for 12 bolt, you will see jdrace is selling a reconditioned 12 bolt posi for $325. He's the best diff. man in northeast Ohio and is a member of the py family. I forgot his handle. He also has a site at www.jdrace.com.
Butch

[big matt]

Thanks for the tip. I actually have his number wrote down. Been meaning to call him. Have a great day.

[Scarebird]

Lock-Rites, while easy to install, are not the best ticket for a street car. The unit in my 71 had a nasty habit of locking in corners - a scary habit. Supposedly they have smoothed down the ramps in the engagement since I had mine.

A Detroit TrueTrac uses helical gears, much smoother engagement and is what modern cars use. No nasty surprises here.