All About Limited Slip Differentials

Some very interesting info from an old Mitsi manual. Might seem heavy going but stick with it and it will help your off-road driving. Wink

LIMITED SLIP DIFFERENTIAL
A limited slip differential is an anit-slipping device which functions as a differential during cornering to allow
the outer wheel to turn at a faster speed than the inner wheel. In the event that one wheel begins spinning
(driving on slippery road surfaces, one wheel leaves the road surface, etc.), it automatically functions to
prevent such spinning.

CONSTRUCTION AND FUNCTION
With a conventional differential, in the event that one wheel of the vehicle is on ice, mud, or some other
slippery surface, the wheel will spin and the drive force of the vehicle will be greatly reduced. If this
happens, the speeds of the differential case and of the side gear (axle shaft) are different because of
differential operation. The limited slip function acts to limit this differential operation. The construction is
shown in the illustration. The multi-plate clutches engage with the differential case and with each of the side
gears. If spinning causes a differenece in component speeds, the frictional force between the clutch plates
will cause the speed of the side gear to become closer to that of the differential case, and thus the limited
slip function will control the spinning. In addition, the purpose of the pressure rings inside the differential :’
case is to transmit the driving force to the pinion gear, and the reason for the separation is to provide an
increase in the clutch plate pressing force through the leverage of the pinion shaft.

OPERATION (TORQUE TRANSMISSION) DURING STRAIGHT DRIVING
When the differential case is turned the drive pinion via the drive gear, the pressure rings which are
interlocked with the differential case will also turn at the same speed. (The projections located on the
outside of the pressure rings engage (with some platy) the grooves located on the inside of the differential
case). When the pressure rings move in the direction of rotation, they contact the tapered portion of the
pinion shaft, and thereby receive reaction force in both the lateral direction and the direction of rotation. The
reaction force in the lateral direction presses the c:lutch plates together, and maintains straight driving.
During such driving, because the road surface gives equal resistance to both the left and right wheels, equal
resistance is applied to the left and right side gears. Therefore, the pinion gear does not revolve, and the
drive gear, the differential case, the pinion shaft, the pinion gear, and the left and right side gears all turn as
one unit.

OPERATION (TORQUE TRANSMISSION) WHEN THE SPEEDS OF LEFT AND RIGHT WHEELS ARE
DIFFERENT
When one wheel is in contact with a concrete road surface (which has high coefficient of friction) and the
other wheel is in contact with a muddy or other slippery road surface (which has low coefficient of friction),
the differential operation will cause the speed of the wheel in contact with the slippery surface to be faster
than the speed of the drive gear, lowering the maximum drive force. If this occurs, the limited slip function
will control the differential operation and increase the driving force. The transmission of torque through the
limited slip device in this event is as follows:
When the differential case is turned by the drive gear and the drive pinion, the pressure rings which are
interlocked with the differential case will turn at the same speed. Also, the difference in the road surface
resistances will cause differential operation and the left and right side gears will revolve at speeds different
from that of the differential case. Because of the friction produced between the clutch plates in mesh with
both the side gear and differential case, one of the pressure rings increases its rotating speed, whereas the
other reduces its rotating speed. The pressure rings press the tapered portion of the pinion shaft with which
they are in contact, and thereby receive reaction force in both the lateral direction and the direction of
rotation. The reaction force in the lateral direction causes the clutch plates to mesh, increasing the frictional
and the drive force.

FEATURES OF LIMITED SLIP DIFFERENTIAL
(1) When one wheel of the vehicle is in contact with ;3 road surface which has poor traction, the limited slip
differential, in comparison to a conventional differential, supplies additional torque to the wheel which
has the better traction conditions by utilizing clutch plates, thus improving the traction capacity.
Moreover, the effect of the limited slip differential is to prevent the vehicle from becoming stuck, even if
the traction of one of the wheels becomes radically reduced.
(2) When one wheel moves from a road surface which has poor traction onto one which has good traction,
or when the wheels are constantly leaving the road surface while driving on a rough, bumpy road, the
clutch plates of the limited slip differential allow the torque to absorb the differences between the
revolution speeds of the right and left wheels. In addition, the sudden changes (jolting) in the drive force
are also absorbed, thus preventing skidding.
(3) Because in the limited slip differential, the differential operation is slightly restricted during normal
cornering, the understeer tendency (the tendency for the cornering of the vehicle to exceed the turning
1 of the steering wheel) becomes greater; however, this does not have any detrimental effect on the
driving of the vehicle. Moreover, in the event that the inside wheel lifts up (the tire leaves the road
surface) during high speed cornering, the clutch plates function to limit differential operation which
would simultaneously decrease the drive force, = of the outside wheel; therefore, the limited slip
differential moderates sudden speed reductions during vehicle cornering, and thereby provides greater
cornering capability than a conventional differential.

MAKING EFFECTIVE USE OF LIMITED SLIP DIFFERENTIAL
Effective Use in Combination with Brakes
If a wheel is in contact with a slippery road surface and has begun to spin, using the brakes in combination
with the limited slip differential will provide even greater traction capability. The resistance caused by the
brakes will further increase the drive torque of the engine, and this increased torque will increase the clutch
plate pressing force of the pressure ring, thus increasing the traction. Also, the drive force transmitted to the
brakes will not function as real drive force. This is shown in the illustration below.
In the illustration, the application rate is Rt = 2, and, supposing the torque from the brake operation is 1. a
drive torque of 1 + 1 = 2 will be applied to the spinning wheel (the right wheel), and a drive torque of twice
that which is applied to the spinning wheel, or (1 + 1) x 2 = 4, will be applied to the wheel which is not
spinning (the left wheel). However, because the brake force of 1 is a negative value with regard to the
propulsion torque of each wheel, the propulsion torque actually obtained by the right wheel is (I + 1) - 1
= 1, and that obtained by the left wheel is [(I + 1) x 2 - I] = 3.
Therefore, the total drive torque is 1 + 3 = 4. In the same circumstances, the total drive torque of a
conventional differential is 1 + 1 = 2, and that of a limited slip differential when the brakes are not used in *.,
combination is 1 + 2 = 3. This represents an increase in the traction by a factor of 2 over that of a.?
conventional differential, and by a factor of 1.3 over that of a limited slip differential when the brakes are not,
used.

NOTES REGARDING SERVICE PROCEDURES FOR LlMlTED SLIP DIFFERENTIAL

(1) The engine must never be operated while only a single wheel is jacked up. Doing so is extremely
dangerous; if the differential functions while the engine is operated at high speed, the oil film between
the clutch plates will decrease, thus causing the friction coefficient to increase, the prescribed torque
ratio will be exceeded, an excessive amount of torque will be applied to the stationary wheel, and the
vehicle will move forward. Also, resistance must never be applied to the spinning wheel.

(2) In the event that one of the wheels comes in contact with a slippery road surface and begins to spin, if
the engine continues to be operated at high speed for too long, the clutch plates might become
abnormally worn; such action must be avoided.

(3) As gear oil, use MITSUBISHI Genuine Gear Oil (part number 8149630 EX) or equivalent. MITSUBISHI
Genuine Gear Oil was especially developed for limited-slip differential use, and is different from ordinary
gear oil. When changing the oil, the oil which is removed will appear considerably blacker than ordinary
oil. This, however, is not a change in color due to the deterioration of the oil, but rather the oil has
become mixed with worn particles of the special treatment on the clutch plates.