From: wesf@boi.hp.com (Wes Fujii)
Subject: Re: Limited-Slip differentials??
Date: Thu, 31 Dec 1992 16:29:05 GMT
Distribution: rec
Organization: Hewlett-Packard / Boise, Idaho
X-Newsreader: TIN [version 1.1.4 PL6]

Stefanos Manganaris (smangan@src.honeywell.com) wrote:
: 
: Hello---Could someone please elaborate on the advantages of a limited-slip
: differential?  What about its internals?  How does it differ from a
: usual differential?  

Advantage:

  1) Both rear wheels (rwd) will try to drive the vehicle, so in low 
     traction or high-performance situations, your acceleration will 
     be much improved.  The "limited slip" portion of it allows for 
     some slip of one wheel relative to the other so when you corner, 
     you won't rip your tires up nor have cornering problems.

Disadvantages:

  1) Higher maintenance - You are supposed to change differential lube
     every 20K miles.  There is a component in the lube that wears out
     rather rapidly that should be replaced.  Most people don't do this
     but it is recommended.

  2) Sometimes the differential will get "locked up solid" so there isn't
     any "limited" slipping.  This can cause either "clicking" noises
     or "jumping" of the front end of the car (on rwd vehicles) while
     turning.  (this is the result of not changing the lube frequently
     enough)  It is not damaging or detrimental to the rear end, just
     annoying.  To remedy the situation, you turn the steering wheel
     all the way to one stop and drive in circles several times.  Then
     turn the wheel the other way to the stop and drive in circles the
     other way.  This should be enough to free the clutches.

  3) Higher cost should repairs ever become necessary.  The reliability
     of the limited slip rear ends is very good so I wouldn't really 
     worry about this.

  4) Sometimes will cause the back end to come around on corners (rwd) - 
     Since both wheels are driven, it is easier to break traction to both 
     wheels simultaneously, especially under marginal road conditions. 
     In that respect, more care should be taken on corners when driving
     in rain/ice/snow. 

  5) Sometimes will cause the vehicle (rwd) to go straight on corners
     during low speed or low traction maneuvers.  This is because both
     axles will be driving the vehicle forward evenly and cornering does
     require that the clutch resistance must be broken.  This will be 
     more apparent on sand/ice/snow.  To minimize this, always have the 
     same tires on the front as you do on the rear.

Internals:

  The limited slip differentials have a set of clutches, gears or cones 
  that connect one driving axle to the other.  Under normal conditions 
  there is no relative motion between axles and the clutches don't do 
  anything.  When one wheel slips, then the clutches will try to transfer 
  driving power to the wheel that is not slipping (about 70% I believe, 
  unless it's a Torsen rear end).  The clutches are there so relative 
  motion can be obtained while cornering.

  A normal diffenential will freewheel from one axle to the other so if
  one wheel slips, all the power is transmitted out (the path of least
  resistance) to the wheel that is spinning.  End result, the vehicle
  just sits there, spinning the wheel (2wd vehicle) that is slipping. 


Opinion:

  The advantage(s) (other people may write in with more advantages)
  definitely outweigh the disadvantages!  I have had vehicles with the
  limited slip option and the performance is MUCH better in ALL
  conditions (keeping in mind the driving characteristics).  For winter
  driving I recommend 4 studded snow tires.  My Trans Am was DY-NO-MITE 
  in the snow and on ice with the tires and limited slip.

  I have another car with limited slip (that I do not drive in the
  winter time).  That performance is very much improved over a non-
  limited slip application.

  I recommend to always get limited slip if it is available.

Wes Fujii
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