If the surface is corroded or if the blades are damaged, replace the impeller

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblySteering Stem Warp Inspection
Whenever the steering stem is removed, or if the steering
can not be adjusted for smooth action, check the steering
stem for straightness.
If the steering stem [A] is bent, replace the steering stem.
Stem Cap Deterioration, Damage Inspection
Replace the stem cap if its oil seal [A] s ...
Hub Bearing Inspection
Since the hub bearings are made to extremely close tolerances,
the clearance can not normally be measured.
NOTE
Do not remove any bearings for inspection. If any bearings
are removed, they will need to be replaced with
new ones.
Turn each bearing in the hub back and forth [A] while
checki ...
Check 3-3: High Beam Indicator Light (LED) Inspection
Connect the leads in the same circuit as Check 3-2.
Connect the terminal [7] to the battery (+) terminal.
Check that the high beam indicator light (LED) [A] goes
on.
If the indicator light does not go on, replace the meter unit.
...