TRUCK SERVICE MANUAL
MASTER CYLINDER AND WHEEL CYLINDERS
It is possible to rehone most cylinders and place
them in good working condition; however, this requires the
use of up-to-date honing equipment. A cylinder hone kit is
available urlder number SE-1679.
Cylinder castings may be degreased or cleaned with
most commercial parts cleaners, provided they are thoroughly
rinsed with denatured alcohol or clean brake fluid to remove
all traces of solvent. Use compressed air or a lint-free cloth to
dry parts after removing them from the cleaning solvent. All
hydraulic parts must be thoroughly cleaned and protected
(after cleaning) from dust or other air-borne foreign material
until reassembly. Do not use cotton waste for cleaning or
drying parts, as particles of lint or thread fibers may block the
compensating ports when cylinder is placed in service.
Clean rubber parts by washing them in clean
denatured alcohol or hydraulic brake fluid.
Do not use minter-base cleaning solvents
such as gasoline, kerosene, distillant, carbon
tetrachloride, acetone, paint thinner, etc. to
clean rubber parts. These solvents attack
rubber parts, causing them to become soft,
tacky and swollen in an extremely short time.
After cleaning, hold the cylinder casting toward a
strong light and sight through the cylinder bore. Blemishes
such as pitting, scratches and visible wear patterns
necessitate unit replacement.
Accumulations of dirt or gummy substances, not
removed during the cleaning process, may be removed with
crocus cloth or jewelers rouge. A hone (SE-1679) may be
used to "clean-up" the cylinder provided its use does not
materially increase the diameter of the cylinder bore.
If master or wheel cylinders must be honed,
remember that the cylinder diameter must not
be materially increased. In other words, scratches and pits in
cylinder walls render the unit useless, as honing the bore
sufficiently to remove them would increase the bore diameter
to the point that new piston cups will not seal properly. The
possibility that the cylinder may have been honed during a
previous overhaul should not be overlooked.
After honing a cylinder and obtaining a
blemish free bore, check the maximum piston
clearance using a 6.35 mm (1/4") wide feeler
gauge with a thickness as follows:
1 1/4-1 7/16
.2038 : .
If the piston can be inserted with the feeler
gauge in the cylinder bore, the unit should be
replaced. If the piston cannot be inserted, the
cylinder may be reused.
Be certain that the honed cylinder has no burr at the
compensating or inlet ports, as it would damage the new
piston cup lip. If a burl or sharp edge is present anywhere in
the cylinder bore, it must be removed.
At final inspection, be certain that the master cylinder
compensating ports are open. A soft copper wire may be
used to probe the compensating port. Do not use a steel wire.
Wheel cylinders should be reconditioned whenever
brake lining is replaced because of the following:
As lining wears, wheel cylinder rubber cups move
back and forth over a new, widened smooth area.
Corrosion and foreign matter builds up on the part of
the cylinder walls where cups do not work.
CTS-2055S Chapter III Page 3
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