|  The
Model SX overdrive is designed to fit Land Rover Series
I, II and III models. It bolts on the aft side of the
transfer case in the area where there is a circular
access cover.
The unit is supplied with a change lever
which protrudes through the right hand side of the transmission
tunnel in exactly the same way as on other Series Overdrives.
 Unlike
previous designs of Land Rover overdrives the "ROVERDRIVE"
unit does not have an exclusive oil reservoir. At the
time of installation a small amount of oil is poured
into the overdrive housing. As the vehicle is driven
oil is pumped from the transfer case into the overdrive
by means of a simple Archimedes screw on the overdrive
main shaft. This incoming oil lubricates the main thrust
bearing in passing and is added to oil in the overdrive.
Surplus oil in the overdrive housing overflows down
the tubular main shaft, lubricates all coupling components
and returns to the transfer case.
This lubrication arrangement has several
advantages over previous overdrives:
-
There are no dynamic seals to leak
and no requirement for an air vent.
-
The overdrive casing can be made compact
as there is no requirement for a large sump to store
oil and dissipate heat. Any heat generated in the
overdrive is carried off in the circulating oil
and dissipates in the main body of the transfer
case.
-
There is only one place to check and
maintain oil level - the transfer case.
 The
Model SX overdrive has a far more robust spline connecting
the overdrive to the gearbox than is the case with previous
designs overdrive for Series Land Rovers. This spline
is constantly lubricated by circulating oil and can
not run dry and fret as was the case in previous designs.
The coupling spline is secured by a hexagon nut and
does not rely on the castellated nut previously employed.
The picture shows the longer more robust "ROVERDRIVE"
input spline on the left and a worn out Fairey spline
on the right.
Range shifting is fully synchromesh and
does not depend on any electric or electronic devices.
The unit is designed to be installed and
maintained using normal shop tools. There are no fragile
needle thrust bearings and three simple deep groove
ball bearings are used to resist internal loads.
All gearing is helical epicyclic using
tooth profiles identical to profiles developed for automatic
transmissions used in North American trucks. This makes
the unit exceptionally quiet in operation. The gears
are generously sized for long trouble free life in adverse
conditions.
 The
steel covers used on the bottom of the Series transfer
case are prone to warp and leak. To improve this situation,
Rocky Mountain has a cast aluminium replacement. This
cover is much stiffer than the original and has fins
to improve transfer case cooling.
The
part number for this cover plate is 839713 and it is
supplied with a new gasket and mounting screws.
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