| Re: [GMCnet] limited slip differential [message #87909] |
Thu, 10 June 2010 04:47 |
Gary Casey
Messages: 448
Registered: September 2009
Karma:
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Senior Member |
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I agree with Carl's conclusion below, but I think some of the explanation is possibly misleading. The whole purpose of a limited slip differential is to apply different torque to each wheel, not the same. An "open" differential will, except for internal friction, apply equal torque to the wheels. If one wheel loses traction it will spin, but the other won't. Resistance to side loading (steering, etc) exists only if the wheel is not spinning. Therefore, an vehicle with an open differential will be have more "normally" since when one wheel spins only half the side traction capability is lost. With a limited slip differential both wheels will usually spin at the same time and therefore loss of steering/side traction will be lost all at once. As far as forward traction one way to look at it is that with an open differential the forward traction is twice the traction of the LEAST tractive wheel and with an LSD the traction is the sum of the lessor and
the greater traction. Therefore the tractive benefit of LSD is greatest when the traction is most different (like one wheel on ice, one on dry paving) and is zero when both wheels have the same traction(example: if one wheel is on ice and has a tractive capability of 100 pounds and the other, on dry paving has 900 pounds and open differential will give you 200 pounds of traction. An LSD will give you 1,000 pounds. On the other hand when on wet grass one wheel might have 300 pounds and the other 400. The total traction would then be 600 vs. 700 pounds, not much difference).
Don't know if that is any clearer than Carl's description, but there it is.
Gary
Jay,
Limited slip differentials theoretically apply power to both wheels evenly. they operate under load and will sense a loss of traction on one wheel and 'transfer' power to the wheel that is getting the most traction. The affect of this transfer depends on the strength of the springs and the condition of the clutch packs in the LSD.
The situation you describe of a tire slipping on a wet road, especially when accelerating while on a painted stripe or a steel grate, will be improved if the other tire has better traction. My experience with limited slip diffs, on rear wheel drive cars, is that you will get much better traction under MOST conditions. The exception being a really slick condition like snow, mud, or ice. If you apply too much power under these conditions, you will break BOTH tires loose and loose directional control. That said, it will be harder to break the two tires loose than one as with an open diff. You just need to be aware of this and step on the gas accordingly.
My other main automotive hobby is Jeeps, and traction is always an issue in off road situations. One of my jeeps has a Detroit Locker in the rear diff and a Spicer Power lock (clutch type LSD) in the front. I don't get into snow or even mud all that often, but I understand that it would be a problem to have all four wheels spinning in those kinds of conditions, especially in an off camber situation. The result would be to slide toward the downhill side, as you have described with the GMC. People who operate their 4-WDs in that type of situation usually use selectable lockers, at least in front, so they can have one tire that is not spinning.
Here is some info on Wikipedia on limited slip differentials;
http://en.wikipedia.org/wiki/Limited_slip_differential
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Carl S.
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