Should I rebuild or replace my brake/ clutch cylinders?
ANSWER - The answer depends
upon the condition of your cylinders and your abilities.
First remember your life and the lives of others depend upon your
brakes working correctly. Never make due with shoddy rebuilds or
poor condition parts. If your cylinder can not be brought back to
like new condition replace it.
The key to deciding whether to rebuild or replace lies in the cylinder's
piston bore and piston conditions. The bores of Lockheed/Girling/Lucas
cylinders came from the factory polished to a high mirror shine
(not honed like most American cylinders). The sides of the pistons
were also polished to a high shine.
Over use, particles can get into a hydraulic system , get lodged
between the piston and bore and scratch groves into the piston bore.
Moisture absorbed into brake fluid or getting past the cylinder's
dust covers while wading may cause corrosion inside the bore (This
is why you should drain and replace the fluids in your hydraulic
systems at least one a year).
The rubber piston seal was designed to slide back and fourth along
a mirror smooth surface. The piston can expand to seal a slightly
larger diameter opening but it can not expand to fill scratch groves
or irregular pitting holes.
When you disassemble the cylinder, wipe out the bore with a clean
dry rag and make a visible inspection. If there are deep groves
or pitting, the cylinder must be replaced. If you think the irregularities
are shallow, repolish the insides of the cylinders and see if they
A one inch muslin polishing wheel on a Dremal tool and white jeweler's
rouge works well for polishing bores (Be sure to blow any rouge
out of the cylinder passages afterwards). If you can repolish the
cylinder bore back to a mirror shine the cylinder is safe for rebuilding.
If you can not, replace the cylinder. If you rebuilt a damaged cylinder
there will be accelerated wear on the piston seal and early failure
of the hydraulic system.
Here are some hydraulic component rebuilding precautions taken
from an old manual on rebuilding Lockheed/Girling components (With
some updating for newer hydraulic fluids):
Always Exercise extreme cleanliness when dealing with any
part of the hydraulic system.
Never handle rubber seal or internal hydraulic parts with
greasy hands or greasy rags
Always use fresh brake fluid from sealed containers
Never use fluid from a can that has been cleaned with gas,
kerosene or other solvents
Never put dirty fluid into the reservoir, nor that which
as been bled from the system.
Always use clean brake fluid of the type that you will use
(DOT 4 or Silicone, DOT 5) or alcohol for cleaning internal parts
of the hydraulic system.
Never allow gas, kerosene, incompatible brake fluid or any
solvent to come into contact with these parts.
Always examine all seals carefully when overhauling cylinders
and replace any which show the least sign of wear or damage.
Always take care not to scratch the highly polished surfaces
of the cylinder bores and pistons. Replace any cylinders or pistons
that have scratches that can not be polished out.
Always use WAKEFIELD/GIRLING rubber grease No 3 (red) for
packing rubber boots, dust covers and lubricating parts likely to
contact any rubber components.
Never use Girling white brake grease or any other grease
for this purpose.
Always replace all seals, hoses and gaskets with all new
ones if it is suspected that incorrect fluids have been used or
the system contaminated with mineral oil, grease or an incompatible
brake fluid. Drain off the fluid, thoroughly wash all metal parts
and flush out all pipes, etc., with alcohol or clean correct hydraulic
Never use anything else for this purpose
Always remember that your safety and the safety of others
may depend on the observance of these precautions at all times.
To this we add:
Never mix Dot 5 (silicone) brake fluid with any other brake
Always replace all rubber components when switching between
regular DOT 3 or 4 brake fluid and Silicone (DOT5) brake fluid.
Some physical properties of the rubber change when exposed to brake
fluid. The rubber seals and hoses react differently with Silicone
than they do with conventional DOT 3 or 4 brake fluid. The combination
of reactions will cause seals to fail.
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