Tracy
and Neil,
In
order to prove to myself that the RPM is
divided between the stacked thrust
bearings, I installed a Hall effect
sensor in the mounting plate and silver
brazed triggers to the middle thrust
washer. An inductive pickup was
installed to monitor the rotation of the
flexplate (input shaft). This allowed
the determination of the input shaft RPM
as well as the middle washer RPM under
various conditions. The load on the
drive was from a 3 blade 72" dia Warp
drive prop with the tip angle set to 20
degrees.
All
new bearing components as used in the -C
drive were tested along with a used
cupped middle thrust washer from a C6
transmission. The cupped thrust washer
was tested because it was possible that
the cup overlapping the 3.5mm shaft side
thrust washer would prevent the middle
washer from contacting and causing wear
of the input shaft. After seeing the
results from the used cupped washer, new
cupped washers were obtained and tested
also.
In
the course of testing the thrust bearing
configurations, it was found that the
reduction drive always operates
completely filled with oil. The added
triggers may have affected the behavior
of the bearing stack due to drag between
them and the surrounding oil. To see if
this was the case, the drive was
modified such that the drive contained
about 5 to 6 oz of oil during operation
rather than the about 20 oz of oil when
completely filled.
The
results are shown in the attached plots.
These
results indicate that, with all new
components including a new flat middle
washer, the RPM was reasonably well
divided between the two thrust bearings
and affected little by the amount of oil
in the gearbox. With the used cupped
middle thrust washer, essentially all
the RPM was seen by the mounting plate
side bearing. With the new cupped
middle thrust washer, the RPM
distribution between the thrust bearings
was affected by engine RPM when the
gearbox was completely oil filled but
little affected by RPM when the gearbox
was drained.
All
the results were obtained with an input
shaft that didn't have a groove worn in
it by the middle thrust washer.
My
conclusion is that with all new bearing
components and unworn shaft the system
behaves as desired. With used
components, the behavior is unknown.
The cupped thrust washer is not a
solution to the shaft wear issue because
of the uneven RPM distribution when
submerged in oil and since shaft wear
has resulted from the bearing cages as
well as the middle washer.
The
internal gearbox pressure with -6 drain
lines was about 4 psi when cold and
about 2 psi when warm which may have
implications in terms of input seal
leakage and the seal coming out of its
bore. The completely oil filled gearbox
consumes extra power which is converted
to heat but apparently not so much as to
cause serious problems.
All
the above are simply results of my
curiosity. You are most welcome to draw
your own conclusions.
Steve
Boese