Hewland NMT, Servicing Instructions, Page: 14 / 40

PAGE 14
© Copyright Hewland Engineering Limited
POWERFLOW DIFFERENTIAL
This powerflow differential unit is designed with versatility as it's major asset. Many factors will contribute to the settings required. A car with
good traction and low power, may require a completely different arrangement to that of a car with poor traction and high power.
There are 10 friction plates within the unit (4 (87) splined to the diff casing (57), and 6 (88) splined to the side bevel gears(84). Slip limiting is
dependant on the friction resistance between these plates, and is affected by clamping the plates together.. Four factors contribute to the total
friction torque between the plates :-
3/ The second adjustable factor is
how tightly the plate stack is
compressed on assembly (known
as static preload). Included in the
plate stack is a preload spacer
(89). The preload torque is
measured between the side bevel
gears, by holding one side bevel
gear (84) stationary, and
measuring the torque required to
turn the other using tool SK-____.
When the diff is assembled, the
preload torque must be at least 10
lbs.ft, but can be much greater if
required. New plates ‘run in’ so a
higher preload is advised than
with used plates.
4/
The final adjustment is simply to
re-order the plate stack so as to
change the number of relatively
rotating faces. The diagram shows
the stack setup with the maximum
12 working faces. Standard stack
may be shuffled to give as few as
2 working faces.
1/ The side bevel gears (84) thrust
apart to clamp the plates as they
transmit the driving power. This
is a feature of the gear geometry,
and is not adjustable.
2/
The ramp angles cut on the side
ring gears (85) have an effect on
how much of the transmitted
torque is converted into sideways
(clamping) force onto the plates.
For example, on the drive side
ramp, 45 degrees transmits less
sideways force than 30 degrees.
Likewise on the coast side ramp,
an 80 degree angle will transmit
little or no clamping force onto
the plates, whereas a 45 degree
angle will transmit a much
greater force. Side ring gears
(85) are available with many
different drive/coast ramp angle
combinations.
FIG URE 6