REFLECTOR: Low Hydraulic Pressure or Pump Check Valve Leaking?

[Bob Jackson]

I’m stuck in Vernal UT after flying from Orlando, heading for Oregon.  After
take-off from Vernal on the third and last leg to Portland, I got an unsafe
gear up light.  After returning and investigating (no problem getting the
gear back down), I noticed the hydraulic reservoir was down more than a
third of the way from the top (we normally keep our fluid level (with the
gear down) about ½” from the top of the reservoir.  I refilled the reservoir
and tried again.  This time I noticed the pump (light) was cycling even on
the ground, and got the same ‘Unsafe UP’ light indication after take-off.

 

Does anyone have an ideas or suggestions?  I assume that the pump can’t
create enough UP pressure because the up-side pressure relief valve won’t
let it.

 

Attached is a PDF copy of the Mercruiser Outdrive Maintenance manual – pg 20
has a good diagram of the internal design of (our) gear pump, including
shuttle valve, pressure relief valves, etc.  Can anyone explain:

1.	why the pump’s tank level is different for the Gear UP and Gear DOWN
directions (isn’t there the same amount of fluid on both sides of the
pistons?)
2.	if you’ve ever seen a situation where the both the UP and the DOWN
sides get pressurized so that neither pressure switch will any longer allow
you to change the gear’s position (different problem from mine in Vernal,
but just asking since I heard of it once)?
3.	What could cause my hydraulic reservoir to go down by 1/3 during
just the first two legs from Orlando, when it’s never gone down rapidly like
that before.  We don’t seem to have any big leaks in the overall hydraulic
plumbing that I’ve been able to find yet.
4.	Is there any way for the hydraulic pump or reservoir to ‘vent’
fluid, other than from bad hydraulic connections that are external to it?

 

Thanks for the help,

Bob Jackson

N2XF

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