There are two different plans for "limited-slip" differentials, that I am aware of:...
they are still limited slip differentials (LSDs). there is no such product as "posi-traction" - it is the brand name given to a limited slip.
... The first limited-slip differential is what you get on the smaller, cheaper pickup trucks and vans, the second is what shows up on the bigger Ford 10.25 inch, and Dana 60 and 70 rears on pickup trucks...
you ever taken one apart? because what your describing doesn't exist in my Ford Dana 80 rear diff with OEM LSD.
you are right, though - there are many many different methods in achieving "torque biasing", which is the technical method for 'limiting torque transfer' which is a fancy way of saying "limiting slip".
the basic style of spring loaded clutch pack type LSD (which you described first) is very simple, very straight-forward, and is what comes in OEM vehicles because it is cheap. also, they don't regulate or control torque transfer very well, which is why they hardly do anything at all.
the more complex LSDs (which, one style, you described second) does a much better job at "torque biasing". there are many different methods (spring actuation, wedges, balls, cones, etc) for applying more torque per revolution, but they all are doing essentially the same thing.
but let's get back to 'torque bias'. this concept transmits a
ratio of torque, not necessarily a force. you see, the simpler style of LSD only creates a certain amount of resistance. for example, say it takes 150ft-lbs of torqe to overcome the clutch pack on the simple LSD [and for the remainder of this post, i'm just using BS #'s for example sake]. that means that when a wheel loses traction, it will take 150ft-lbs of torque from the input torque and effectively transfer it (by
resistance) to the wheel that has more traction. sometimes this is enough. often, it ain't jack and just gets you into further stuckness.
the more complex LSDs have a designed 'torque bias' - this means they transmit a ratio of torque to thru the diff relative to the input torque and rotational speeds. example, say you have an Auburn LSD and it has a maximum bias of 4:1 - that means it will transfer approximately 75% of the torque and retain about 25% at full gain. so if you input 500ft-lbs to your diff while trying to get thru the mud, then it will send (again, by resistance) about 125ft-lbs to the wheel w/ traction. but send 1000ft-lbs down the pike and it should send about 250ft-lbs to the traction wheel. this is also the style of LSD that should help by using the P-brake or by applying the brakes. that is a method to help increase the amount of torque at the traction wheel. so increase the input to 2000ft-lbs and you are now sending almost 500ft-lbs to the traction wheel.
now, this is all best case and there are definite limits on design ranges - send 6000ft-lbs down the pike and you're not going to get 1500ft-lbs of torque transfer. it will likely just sit and spin and burn up clutches. but the principle is the same. different LSDs have differing torque biases, anywhere from 5:1 - 3:1. and as clutches wear, they lose torque holding ability.
now the only other animal that could be described as somewhere between an LSD and a locker is the Torsen LSD. this is the design basis of the TruTrac diff, originating from the design by [then] Zexel-Torsen. there are no spider gears; they use an arrangement of helical gear to both transmit and control torque thru the diff. there were a couple different biases based on the gear cuts used, but some (given enough input torque) would actually lock-up and trasmit 100%. we had one in our mini-forumula car out of an old subaru: while turning, the RPM difference between shafts was not enough to bind the gears, but lose all traction on one and it would lock up solid. these aren't made anymore (except for the TruTrac, which has a max bias of around 2.5:1 IIRC) and they were very expensive. but, the all-gear design made them very rugid, maintenance free, and extremely reliable.
so if i had to desire an LSD, i'd go w/ a TruTrac based on design and service life (infinite). but, i don't think i would given the selection and performance of lockers available today; especially the "lunchbox lockers" like the Soft Locker and the Gearless Locker - these two supposedly have great street maners and don't cost much, either. but for something like the deuce, the UltraLocker (an improved Detroit / No-Spin) is the no-brainer for reliability and performance. i drive mine [bob'd] on the street and rarely hear a peep out of it once i adapted my driving style. just for curiosity sake, i left the front hubs locked to see if i'd notice any binding while turning (with
out the front axle locked in) - never noticed anything. quite frankly, that surprised me the most. maybe because i have power steering?
diffs and traction aids are cool, and in some there's a lot of tech in them. ironically though, few have any "new" technology...
