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Laymen's Term discussion on posi.

This is a discussion on Laymen's Term discussion on posi. within the Firebird / WS6 forums, part of the Vehicle Specific category; Hey, I guess I don't really mean for this to be a discussion as opposed to a really simple question ...

  1. #1
    Member Ant71130's Avatar
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    Laymen's Term discussion on posi.

    Hey, I guess I don't really mean for this to be a discussion as opposed to a really simple question or series of such. I understand a lot but I just want a few scenarios played out; I googled, searched and found a lot of good info on differentials and the torsen that I evidently have, but I do have a few questions I'd like someone to explain simply with straight up answers.

    All 4th gen V8's came with a LSD right? And 99+ had the torsen 2:1 posi I think? First, how exactly does the car measure the ratio on adhesion to traction loss, or I guess I could just say friction in general? Does that mean if one tire has more than twice the torque of the other going to it that it will keep spinning regardless or is that backwards?

    Also, it's my understanding that a posi unit, if hypotetically were placed halfway on ice and the other on pavement, would still move because regardless of the lack of friction on the ice, the other tire would still spin correct? And if both tires were on pavement, it does a two wheel burnout and not a one like an open differential would do because they essentially demand that both wheels spin equally right? Or rather require it to have friction qually in order to spin both. So what happens if neither tire has traction or say, both are on slush or ice. Do both tires just spin freely? I only ask this because I had my car in snow, parked, once and I could have swore that when I tried to roll out of it, only one of my tires spun (the driverside I think). I may have been mistaken but I think friends told me that too. Or does that have something to do with the 2:1 ratio? I just want basic answers because I'll understand it a lot better if I know the answer, I can create the reasoning and process on my own lol. Maybe lay out some stuations in which things would be different.

    I was scared when I remembered the ice moment that my posi was broken because usually if I get on it hard, I tend to go sideways a little bit. I literally 10 minutes ago drove to an empty strip, layed on it and checked for rubber. Two strips . So I guess I'm good there, it may seem to go a little sideways because it is lowered withOUT a new PHB and has 4.10's in it so, perhaps it's a torque+weird weight distribution thing. Around a corner I can kick the ass out no matter what, be it on snow or glue for all intensive purpouses lol. So I'm assuming my posi is ok.

    Sorry this turned out to be a huge read, I didnt intend that but please, anyone can chime in
    Last edited by Ant71130; 10-05-2011 at 06:32 AM.
    2002 Black/Ebony M6 WS6: Lid, Filter, Smooth Bellow, P&P TB (!Bump Stop), Magnaflow Cat-Back (dumped after the axle), 4.10s, Hypertech ME Tune, eibach springs 4/4, LCA relocating brackets, PHB, free mods, 17" TTMs.

  2. #2
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    Unfortunately, alot of marketing hype has made more confusion out of what is really a simple concept. I'll take a stab.

    All differentials (non-posi) split the torque equally between the driven wheels. If both wheels have equal traction, they will "absorb" the same amount of torque from the driveshaft before spinning (losing traction). However, if one of the wheels has less traction than the other, that wheel will spin first once the torque delivered to it overcomes the available traction. By default, the torque going to the opposite wheel will be the same. The result is the wheel with less traction begins spinning, and the other is "starved" of torque is not spinning. This is a good thing for inexperienced drivers who don't know how to handle a fishtail (one non-spinning wheel maintains lateral traction), but sucks if one of the wheels is on ice (very little torque going to the other wheel with the traction). But if traction on both wheels is exactly the same, it is possible for a non-posi differential to lay down 2 stripes from a burnout. However, it is rare that traction on both wheels are exactly the same.

    ALL posi / limited slip / LSD differentials operate basically the same way with one very important difference. A friction component (be it clutch packs, cones, meshing gears , what ever) RESISTS the differential MOTION between the two wheels, UP TO A CERTAIN POINT. All that means is that the torque provided by the driveshaft is no longer EQUALLY split between the 2 wheels. When one wheel gets less traction than the other and begins to slip, the friction component resists the differential MOTION between the wheels and prevents the opposite wheel from being "starved" of torque. The result is usually the wheel with more traction continues getting more torque until it too loses traction, then both wheels spin. However, there is a point at which the friction component cannot overcome the difference in torque being absorbed by the two wheels and then it can no longer resist differential motion. When this happens, one wheel will begin spinning faster than the other. Short of a LOCKING differential, a limited slip friction component can only transfer just so much torque to one or the other wheel. So in cases where traction at the 2 wheels are extremely different (dry pavement vs ice), if too much torque is applied by the driveshaft, the wheel on ice will spin, even w/ limited slip.
    Last edited by JohnnyBs98WS6Rag; 10-05-2011 at 11:27 AM.

    Johnny B - '98 "Triple Black" WS6 Convert, M6, All Options, ASC #3030 (1 of 50)
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    Member Ant71130's Avatar
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    Ok, really appreciate what you typed that did explain quite a lot. Only thing I don't really know is what those friction components are, or how exactly they work. Not sure mechanically how it resists but at least now I understand the result of it.

    Now what scared me was I didn't put the 4.10s in my car, I would have waited for a 12 bolt/9" to do that, so (knowing little about diffs obviously) I got spooked that whoever did didn't put a posi system in or that mine was broken. However, changing the gears only doesn't actually change the differential right? So I should be okay? The ring and pinion aren't involved in the posi unit? Or are they... idk lol.

    AND, what about when BOTH tires can't get traction, what happens to an open or LSD then? Because as I stated, I thought only one of my tires spun.

  4. #4
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    I can't imagine anyone installing 4.10s and swapping out the diff for a non-posi unit. And yes, changing the ring & pinion changes the just gear ratio, but not the differential. But that's no guarantee that a new diff was not installed when they put in different ring/pinion. The ring gear bolts to the flange of the differential. The differential contains the friction components (clutch pack, cones, whatever) that limits the slip.

    If both tires are on ice and have very little traction, a LSD will definately cause them both to spin, a non-LSD diff might or might not. Again, odds that both tires have exactly the same amount of (even miniscule) traction is very low, so w/ a non-LSD diff, the tire with the least traction will spin, or might just spin faster. It would not be unusal for a non-LSD car to spin one wheel at first, then as the car moves a little and the tables are flipped so that the opposite tire gets more traction, it will stop spinning and the other tire will start spinning.

    The best way to test your posi, is to raise both rear wheels in the air, put the car in park (or gear if an M6) w/ the engine off. Release the e-brake, and then try to spin one of the rear tires. If you have a non-posi (or a posi that is really worn-out), the tire will spin easliy and the opposite tire will spin in the opposite direction. If your posi is good, it should take ~100 ft-lbs of torque or more to get the tires to turn.
    Last edited by JohnnyBs98WS6Rag; 10-06-2011 at 10:39 AM.

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