Figure 23-4. Brake Band.
transmission case so that the element can act as a
seal around it to prevent leakage of hydraulic pressure
and is spring loaded to allow quick release of the band.
Some servos use hydraulic pressure on both sides of
b. Construction (Fig. 23-5). The brake band is
their pistons so that they use hydraulic pressure for both
the release and the application of the band.
comprised of the following elements:
c. Operation (Fig. 23-5).
(1) Band. The brake band is a circular
(1) Released. When the brake band is
piece of spring steel that is rectangular in cross section.
released, there is no hydraulic pressure applied to the
its inside circumference is lined with a friction material.
servo and the drum is free to rotate within the band.
The brake band has bosses on each end so that it can
be held and compressed.
(2) Applied. When the brake band is
(2) Drum. The drum fits inside of the band
applied, hydraulic pressure is applied to the servo which,
in turn, tightens the band around the drum. The result is
and attaches to the planetary gearset element that is to
that the drum is locked in a stationary position, causing
be locked by the band. Its outer circumference is
an output change from the planetary gearset.
machined smoothly to interact with the friction surface of
the band. By pulling the open ends of the band together,
the rotation of the drum stops.
23-7. Overrunning (One-Way) Clutch (Fig. 23-8).
The overrunning clutch is used in certain automatic
(3) Anchor. The anchor firmly attaches
transmissions to lock a planetary gearset element to the
one end of the brake band to the transmission case. A
transmission case so that it can act as a reactionary
provision for adjusting the clearance between the band
member. The operation of the overrunning clutch is the
and the drum usually is provided on the anchor.
same as that of the one used in the torque converter
(para 21-7), and it can be of the sprag or roller type.
(4) Servo. The servo uses hydraulic
There is no control system necessary for this
pressure to squeeze the band around the drum. The
servo piston is acted on by hydraulic pressure from the
valve body that is fed through an internal passage
through the case. The servo piston has a