17
Section 2
Hydraulic Brakes
Wheel Cylinder Diagnostics
There are two types of wheel cylinder problems:
1. Leaks
Cylinder leaks can be caused by:
a. using the incorrect type of brake fluid
causing the seals to leak,
b. corrosion or damage on the surface of
the cylinder bore,
c. worn or oversize cylinder bore, and
d. damaged seal cups.
To find leaks that are not immediately
visible, pull back the cylinder boot. A small
amount of fluid on the inside of the boot is
normal. Unless other conditions causing
poor brake performance are known, the
wheel cylinder must be checked.
2. Poor Cylinder Action
Cylinder binding can be caused by:
a. Corrosion or deposits in the cylinder
bore.
b. Swollen cups caused by contaminated or
wrong type of brake fluid.
c. Cups wedged into excessive clearance
between the piston and the cylinder
bore.
d. Wrong type of pistons for push rods or
brake shoe ends. Figure 2.19.
Figure 2.19
BOOT
ASSEMBLES ON
FLAT PISTON
FACE
PISTON
PUSH
ROD
ASSEMBLES IN
PISTON SOCKET
BOOT
BRAKE SHOE END
PISTON
CYLINDER
CUP
CYLINDER
CUP