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Old 11-14-2010, 06:51 PM
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Chevy 12 bolt posi working properly?

Hey guys I was wondering if you could tell me if I set up my 1968 Camaro 12 bolt posi properly? I changed the ring and pinion and added a posi unit to my car 15 years ago. When I do a burn out both tires spin. My question to you is when I have the car jacked up why does the rear wheels spin in opposite directions. I spin the right wheel forward and the left wheel spins backward. My buddy's olds 442 has posi and his wheels spin the same direction. If you hold one wheel the other won't spin. Mine if you hold one wheel the other will spin. We put a new clutch pack in when it was installed. Does the clutch plates need adjusted? Thanks

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Old 11-14-2010, 08:32 PM
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Probably didn't get the clutches shimmed tight enough. Too much oil additive can also make it slip easier. Which clutch set did you use?
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Old 11-17-2010, 10:30 PM
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i dont see the issue here, if you got both wheels spinning then its probably fine, if its truly a posi unit and not just a limited slip unit(in which then would only give power to the tire thats not slipping more, than the other wheel)
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Old 11-17-2010, 11:03 PM
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Limited slip and posi are the same thing. Posi and Positraction are Eaton's brand names for their clutch type limited slip differential. A standard differential will spin one wheel.
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Old 11-23-2010, 06:48 PM
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Big Gear Head, thanks for the help. Here is what we figured out. We tore apart the differential and the clutches are OK. My buddy drag raced most of his life and when he set up the rear end he did not use the shims and preload springs. This causes the rear tires not to be locked together when up in the air. This setup is supposedly the better way to go. We put the car in gear and held one tire and tried to spin the other and it would not turn. Posi unit is actually working the way it should hence the double wheel burnout. Thanks for taking the time to answer my question. The knowledge on this site is invaluable.
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Old 11-23-2010, 08:53 PM
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spool or not to spool

maybe your buddy had a spool rear end and not a clutch type rear end ,plus to the posi still has spider gears and when unloaded the wheels will spin seperate until the weight come down ,try air locker
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Old 11-23-2010, 11:26 PM
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Leaving the springs out is all right as long as the clutches have the correct preload. Leaving the shims out is not all right. The shims are how you set the preload on the clutches. If the preload is not correct you will not get the grip that you need from the clutches, but even more important is that it can cause the gears to break. If the clutches don't have the correct preload then the gears are running closer to the ends of the teeth, which is the weakest part. Shimming the clutches moves the teeth deeper, which makes them stronger. Incorrect preload also increases axle end play.
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Old 11-24-2010, 06:42 PM
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He added an extra clutch in place of the shim to get the proper pressure back when it was setup. We checked the backlash and it is .09 which is in limit. We also looked at the gear mesh and there isn't any wear at all. The setup is good. It is working the way it should. I am relieved.
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