question about posi differentials - Pontiac GTO Forum
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post #1 of 12 (permalink) Old 12-20-2009, 08:15 PM Thread Starter
 
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question about posi differentials

My understanding of positrac rear diffs is that when the right wheel slips you get traction to the left. with a standard diff you get power only to the right. since i'm not sure what i've got, and i noticed something yesterday, i'm hoping for a bit of an explanation.

I threw the car into reverse while parked on some damp grass. Wheels slipped and when i pulled away i noticed two bare spots. will a standard differential send power to both wheels in reverse, or do i have a posi differential?

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post #2 of 12 (permalink) Old 12-20-2009, 08:47 PM
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It is possable to get both spinning with an open rear end, but it's rare and conditions would need to be just right. To be sure if you have an open or a posi, put one tire in the gravel/ice and one tire on the pavement, gun the throttle, if just the one tire spins it's an open, if both spin, it's a posi.
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post #3 of 12 (permalink) Old 12-20-2009, 09:03 PM
 
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with the standard open diff the wheel that spins is the one with the least resistance. the right tire spins most often because the rotation of the engine is trying to lift it up while pressing the left one down. if traction is equal either one or both can spin.
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post #4 of 12 (permalink) Old 12-20-2009, 09:55 PM Thread Starter
 
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gravel and pavement, got it... will report back

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post #5 of 12 (permalink) Old 12-21-2009, 08:53 AM
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Since the gravel/blacktop scenario gives you an excuse to spin the tires, you could just do a power brake too....
Of course that is harder on driveline components and if it is an open diff and only 1 wheel spins, you don't want to do that for long. The spider gears inside the carrier have no bearings to carry the load and with only 1 axle/side bearing spinning, it can over heat and cause damage to the gears and carrier. It's the Newtonian effect of a non-compressible fluid being forced out of the contact stress area due to non-forced circulatory lubrication.....

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post #6 of 12 (permalink) Old 12-21-2009, 09:04 AM
 
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Just jack up the rear end and spin the tires by hand.

non-posi should turn the opposite from each other.





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post #7 of 12 (permalink) Old 12-21-2009, 09:13 AM
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Quote:
Originally Posted by Bobbyg View Post
Just jack up the rear end and spin the tires by hand.
Phffffttttt........that's no fun, Bobby. He wants to mash the throttle, hopefully hear a tire howl and see smoke......

Mitch
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post #8 of 12 (permalink) Old 12-21-2009, 09:24 AM Thread Starter
 
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Quote:
Originally Posted by Too Many Projects View Post
Since the gravel/blacktop scenario gives you an excuse to spin the tires, you could just do a power brake too....
Of course that is harder on driveline components and if it is an open diff and only 1 wheel spins, you don't want to do that for long. The spider gears inside the carrier have no bearings to carry the load and with only 1 axle/side bearing spinning, it can over heat and cause damage to the gears and carrier. It's the Newtonian effect of a non-compressible fluid being forced out of the contact stress area due to non-forced circulatory lubrication.....

now THAT'S an answer I can understand

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post #9 of 12 (permalink) Old 12-21-2009, 11:29 AM
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Originally Posted by xcmac26 View Post
now THAT'S an answer I can understand
Thank you............
Thank you............
Thank you very muuuuuuuuuuuch.......

Mitch
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post #10 of 12 (permalink) Old 12-21-2009, 12:12 PM
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Still waiting to hear about what diff you have. O'yeah, you're probably at work. Say, who's that looking over your shoulder??!!



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