Repair - Manitowoc Grove CD3340B Service Manual

STRUCTURAL
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a2210
Dual Brake System - Operation
When hoisting a load, the brake clutch, which connects the
motor shaft to the primary sun gear, allows free rotation. The
sprag cams lay over and permit the inner race to turn free of
the outer race (Figure 11-84). The friction brake remains fully
engaged. The hoist, in raising a load, is not affected by any
braking action. See Figure 11-81.
When the lifting operation is stopped, the load attempts to
turn the primary sun gear in the opposite direction. The
11-34
reverse input causes the sprag cams to instantly roll forward
and firmly lock the shaft to the fully engaged friction brake
(Figure 11-72).
When the hoist is powered in reverse, to lower the load, the
motor cannot rotate until sufficient pilot pressure is present to
open the brake valve. See Figure 11-68 and 11-69. The
friction brake within the hoist will completely release at a
pressure lower than that required to open the brake valve.
The extent to which the brake valve opens will determine the
amount of oil that can flow through it, and the speed at which
the load will be lowered. Increasing the flow of oil to the hoist
motor will cause the pressure to rise and the opening in the
brake valve to enlarge, speeding up the decent of the load.
Decreasing this flow causes the pressure to lower and the
opening in the brake valve to decrease, thus slowing the
descent of the load.
When the main control valve is shifted to neutral, the
FIGURE 11-71
pressure will drop and the brake valve will close, stopping
the load. The friction brake will engage and hold the load
after the brake valve closes.
When lowering a load very slowly for precise positioning, no
oil flow actually occurs through the hoist motor. The pressure
will build up to a point when the brake will release sufficiently
to allow the load to rotate the motor through its own internal
leakage. This feature results in a very slow speed and
extremely accurate positioning.
The friction brake receives very little wear in the lowering
position. All of the heat generated by the lowering and
stopping of the load is absorbed by the hydraulic oil where it
can be readily dissipated.

Repair

Removal
FIGURE 11-72
1.
Be sure hydraulic pressure is relieved in the hoist circuit
2.
3.
Published 04/07/2015 Control # 569-00
Remove the wire rope from the hoist drum.
IMPORTANT!
before disconnecting any hydraulic lines.
Disconnect hydraulic hoses from the hoist motor and
motor drain ports.
Securely fasten an overhead hoist to the hoist assembly.
Remove the hoist mounting hardware and then remove
the hoist.
CD3340B/YB4411