Mercury MerCruiser Service Manual page 537

Symptom
3. Steering is stiff and hard to turn,
even when the vessel is not moving.
4. The helm unit is bumpy and requires
too many turns from port hard‑over to
starboard hard‑over.
5. Steering is easy to turn while
stationary, but becomes hard to turn
when the vessel is underway.
6. Drive drifts to port or starboard while
vessel is underway, even when the
wheel is not being turned.
7. Turning one steering wheel causes
the second wheel to rotate.
8. Seals will sometimes leak if steering
system is not vented at uppermost
helm.
9. Vent/fill plug leaks when turning to
port.
90-8M0099748 eng DECEMBER 2015
Cause
Steering cylinder pivot
bushings are too tight or
trunnion is bent, causing
mechanical binding.
Restrictions in hoses.
Air in hydraulic fluid.
The wrong hydraulic fluid
has been used to fill steering
system.
Dirt in inlet check valve of
helm pump.
Steering wheel is too small.
Incorrect setting of trim tabs,
if equipped.
Dirt in check valves.
The helm has a field‑replaceable wheel shaft seal that can readily be replaced by
removing the steering wheel and seal cover held in place by three small screws.
Quad ring No. 210 is supplied in Seastar® Helm Seal Kit HS5151.
Cylinder rod extended during
filling.
© 2016 Mercury Marine
Compact Hydraulic Steering
Solution
To test, disconnect the clevis from the steering lever
and turn the steering wheel. If it does not turn easily,
repair trunnion or loosen pivot bushings. Note that
excessively loose connections to a steering cylinder or
steering lever can also cause mechanical binding.
Find the restrictions and correct them.
Refer to the filling and purging instructions.
Drain the system and fill with approved hydraulic fluid.
Replace the helm unit.
Fit a larger wheel, if possible. Refer to the installation
instructions. If the problem cannot be rectified by
changing the steering wheel, proceed with next cause
and solution or consult the factory.
Adjust tabs, if equipped.
Remove the check valve plugs. These are the larger
plugs on either side on rear of the helm. Clean the ball
seats and balls, and reassemble.
NOTE: Be prepared to lose a certain amount of
hydraulic fluid during this procedure. Have a small
receptacle available. Refill the system when the check
balls have been reassembled.
Ensure that the cylinder rod is retracted during filling.
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