Gimme a Brake III
by Jim Lunson
One last thing on brakes - changing the fluid. I said earlier that DOT
3 and 4 fluids need to be changed every few years because they absorb
moisture that can rust and corrode the insides of brake cylinders,
calipers, and lines. This periodic bleeding is important,
especially with a timeless car like our MGs where years of ownership
slip by very rapidly as there is little attention paid to the age or
model year and the driven mileage is usually low. And rust and
corrosion creep up very slowly and are rarely noticeable until a
disaster strikes. The way to do this fluid change is to bleed out
the system, slowing replacing all the existing fluid with new.
This process is a fairly easy step to do, but takes a
little time, patience and willingness to reach up under the car.
The process begins by bleeding out the system from the brake farthest
from the master cylinder - the right rear brake (unless your car has
right-hand drive in which case its the left rear). Start by
filling the master cylinder with new, clean fluid, and begin by bleeding
the system at this first bleed screw until the fluid comes out clear.
This is best done by using a 3/16" clear plastic hose so you can easily
see that the fluid coming out has no bubbles and can tell when it
changes from a rust colored brown to clear. This first brake
usually takes significant fluid to change as it is flushing all the old
fluid from the master cylinder, most of the pipes and the brake at hand.
These rear brake bleed screws are also the ones hard to reach as they
are inside the rear tires and getting to them involves obstacles like
the rear axle, emergency brake cable, and exhaust pipes. It takes
a little stretching to get back there.
Once, the fluid running out clear from this brake you
are well on your way to flushing out the entire system. Tighten up
this bleed screw and move to the next farthest brake and repeat the
process. This time it is amazing how little fluid needs to be
removed before clear material flows out. Then on the next farthest
brake and again, only after few bleeds, you will be done. And
finally, the fourth and closest brake is last. Once this one is
done, the job is complete and ready for another 3-5 years of safe
To assist the process, there are several brake
bleeding systems available for purchase. They are designed to
facilitate the process by being able to accomplish the job with only
person, but still involve the same operation. They work by using
air pressure to force new fluid through the system and out the open
bleed screw. I have used both a system that works off the air
pressure in the tires attached to a special cap on the master cylinder,
and a system that has a hand pump at the bleed spot to induce a vacuum
in the system, sucking out old fluid. There are several variations
on these mechanisms available. They work, but I have found them be
usually be more trouble than they are worth to set up. Plus they
also require maintenance when they are only used every 3-5 years or
greater. What they do, when they work properly, is to allow one
person to reach under the car at the brake to be bled, open the screw
and let the fluid flow out until it is clear and contains no bubbles and
shut the system when complete. You still have to hit all four
brakes to get the job done.
I personally prefer the old tried and true brake
bleeding system of using two people, in my case, my trusty mate, Ann.
A child, mother, neighbor or any assistant also works well as the
task required by this person is not real complicated, consisting of
sitting in the drivers seat, stepping on the brake pedal when requested
and then releasing it, also when requested. I do the hard part,
including the reaching up under the wheels.
works like this: attach the clear plastic hose to the brake to be bled.
Insert the end of the hose into a jar with about one inch of old fluid
in it, making sure the hose end is submerged in the fluid. Then
open the brake bleed screw about 1/2 turn. Then ask the trusty
assistant to slowly step on the brake pedal until it goes all the way to
the floor. Observe the fluid that flows out the tube into the jar.
When the pedal reaches the floor, the fluid stops flowing, then tighten
up the bleed screw as it was before starting. Then have the
assistant release the brake pedal. Repeat this
the fluid in the tube runs clear. The only change to this cycle is
that after about 5 repetitions, you need to get out from under the car
and make sure the master cylinder remains full of fluid or refill it as
necessary. If the fluid level here gets too low, air bubbles will
get sucked into the system, and additional bleeding will be required
until they are flushed out. Usually 3 to 4 pumps are sufficient to
flush even the farthest brake, and the closer ones only usually take
about two pumps to finish. Not too complicated and lasts for
The only two possible complications occur in that the
brake pedal probably has not gone all the way to the floor in a long
time. Note I say to push it in SLOWLY, especially the first time.
Often the hinges, and pivots in the pedal mechanism may be stiff from
non use to their maximum range and could break if forced too suddenly.
Also, the master cylinder piston has probably not gone its full travel
length for some time either and if forced too suddenly, can break the
seals on it. So proceed slowly with that first brake pump.
The other complication occurs if the bleed screws have not been opened
for a long time and may have frozen. Sometimes, a penetrant will
free one to turn; otherwise, it is likely to break off when a wrench is
applied. This will open the system immediately and all the fluid
will drain out. So if you have trouble turning a screw, make sure
you have another large jar ready to catch a lot of fluid coming out.
Plus then you have to remove the broken bleed screw and replace it with
a new one; a much more complicated task. A test of whether the
screws can be loosened is advisable before the process is begun.
Then you will be ready without this one surprise. One last note,
brake fluid is hard on car paint finishes, so be careful when filling
the master cylinder not to spill any, or cover the fender to protect it
I have discussed flushing the brake system as a
maintenance step, but the brakes also need bleeding if there is a
problem and air has entered the system. This can occur either due
to a leak somewhere, or if the fluid level in the master cylinder gets
too low. This bleeding step is the same as outlined above, and
should be done if the brake pedal feels spongy, or gets soft after being
applied during a prolonged stop. So check your brakes again, find
out when the last time you changed out the fluid, and spend some time
keeping the car running (and stopping) in tip top shape. Again,
this is a step that is easy to ignore, but is crucial to maintaining our
MGs. Plus it is a step that most shops charge up to $150 to
accomplish (takes two people, remember.) So this winter, find an
assistant and get busy on those brakes.