RE: Limited slip correction

[QSHIPQ@aol.com]

Mr. Selby writes:

>>>>I have used the brake trick, the poor mans locker, on both two and four 
whel drive, limited and unlimted slip differnetials.  (Never owend a locker 
equitped vehicle until my present 86 4kcsq.)  You have to apply the brake a 
lot more on an unlocked differential as opposed to a limited slip.  On 
Hummers, which use a 2 torsens and a manually lockable center (but 
unlimited) diff.  The procedure if one starts to lose traction is to apply 
the brakes gently to redistribute the torque to all four wheels, so I guess 
it is a matter of careful application.
I believe the statement in your first paragraph is correct, if you have 
three torsens then you would be no better off than with two wheel unlimited 
slip diffs.
Basically all the limited slip or Torsen diff does is to promote stability 
in moderate slippage conditions.  When you have a 0 torque spinning wheel, 
however, they can't do nothin' for ya man.
>>>>

A couple of thoughts come to mind reading your posts George.  First, a 
spinning wheel can deliver torque, traction and acceleration.  The definition 
of "laying a patch" (remembering my old days in the 350nova open diff).  A 
quick visit to any drag strip can confirm that a spinning wheel does have 
torque.  For clarification in an open diff, any excess engine torque goes to 
the spinning wheel, and effective Trg (torque ring gear = engine torque) 
decreases.  The maximum amount of torque supported by both wheels is limited 
to twice the amount of torque supported by the spinning wheel (see:  
http://www.mindspring.com/~audidudi/Torsen.htm for more information)

The 4wheel ETS (Mercedes) does apply braking to 3 of 4 wheels to get a stuck 
vehicle out of the slick.  The torsen can send up to 3 times the amount of 
torque to the other axle.  Many off road guys (Toyota list for many stories 
here, or I suppose the hummv list) use the brakes while scrambling for 
maximum traction.  Mucho easier to accomplish with an autobox than with a 
stick, since the torque converter really is the best progressive clutch for 
this, and most offroad boys (the crawlers not the racers) use torsens with 
autoboxes.  The braking does transfer the torsen, and is very effective.  
However, in more high speed manuevers, it should be noted that the torsen has 
already shifted torque by the time you realize a spinning wheel.  I might 
also add, that a torsen center can sometimes be fooled into shifting torque 
in/appropriately do to front and rear slip angle differences as well.  See 
volumonus archives on this subject for more.

IME, in slow speeds the braking does affect the torque shift of a torsen, 
center or otherwise.  I have also found that in a classic race turn scenario, 
applying the brakes during a torsen shift scenario, is far from comforting to 
the driver instinct, and increases the chance that you will lose it all 
together.  This would apply to all center limited slip differentials with 
less than 100% locking.

HTH

Scott Justusson
'87 5ktqwRS2
'84 URQRS2
'87 4Runner turbo
'85 FJ1387cc (spins it's only tire with lots of acceleration)