This post gets into the charge pump, which supplies
hyd fluid to the suction
side of the
HST pump, and the implement pump.
The charge pump (first pic) is mounted to the front of the
HST and is always
driven at engine speed by the drive shaft, even when the
HST has no demand
(foot off the go pedal). This takes up a few
hp, further sapping some of the
engine power seen by the
PTO, even when the tractor is not moving. Looking
at the pump, I saw scoring of the aluminum case, and the steel rotary gears.
This can be attributed to the fact that this pump draws oil from the reservoir thru
a steel mesh screen, which did not completely exclude the metal particles that
got into the oil from the disintegrated main gearbox. The charge pump only
operates at a couple hundred psi, and this one may suffice, but I was not
comfortable re-using it. Another $300 for a new pump.
The second pic is a little blurry, but it shows the implement pump, which I
opened up to check. It is in fine condition, thanks to good filtration. The
diverter valve sends oil to the power steering valve, and excess oil (when not
steering) supplements the flow from the charge pump to the
HST. The
HST's
oil from the charge pump is filtered again, explaining the lack of damage to the
HST. In the past with older cars, I liked to open up the engine oil pumps to
check for scoring, which gave me some indication of how well the previous
owner(s) cared for the car.
Next: look, Ma, no gears!