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