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