Checking the condition of your car's brake pipes is a job that is all too
easy to forget because the pipes are mostly hidden underneath the car. However,
these pipes can deteriorate to the point where they start to leak, causing a
dangerous loss of
and eventually partial or even complete failure
of the braking system.
If you find that you need to keep topping up the brake fluid
often than usual, then there is a leak somewhere in the brake system. You
should immediately check the whole system thoroughly to find and repair the
source of the leak.
If you find a fluid leak at one of the unions joining a rigid brake pipe to
, you may be able to stop it simply by tightening the
If this fails, or if the pipe itself seems to be the source of the leak,
then the only cure is to replace that section of pipe. But you should first
check the condition of all the brake pipes because you will probably find that,
if one pipe has become so corroded that it has started to leak, the other pipes
will also be in poor condition. The only safe course then is to replace all the
Make a systematic check of all the pipes by starting at the brake fluid
reservoir and working down towards the brakes themselves, checking each length
of pipe in turn.
Wipe the pipe clean of any oily deposits, then run your hands along the pipe
to feel for damage - in particular if the pipe feels flattened or corroded at
any point. If the surface feels rough because of corrosion, rub it with fine
wet-or-dry paper or use a wire
to see how deep the corrosion goes. Light
surface rust is acceptable but if the rust has eaten its way into the metal,
the pipe has to be renewed.
Where a pipe passes through a bulkhead, check that the grommet holding it
there is still in position. If the grommet has come out the pipe will chafe
against the side of the hole and may wear through. Make sure the pipe is not
damaged and if all is well relocate the grommet. You can glue the grommet in
place with impact adhesive if it is prone to becoming loose.
Types of union
In most modern cars, the unions between the pipes and
are metric, but
you may have an older car that is fitted with imperial thread unions. If you
are in doubt, it is important to find out before you start work which type your
car has because the
on the ends of the pipes are shaped differently
depending on whether the union is metric or imperial.
One way to find out is to ask your car dealer, who should be able to tell
which fittings your car has from its
Alternatively, you can find out yourself by examining the unions for clues.
On a union with an imperial thread, the female nut (the one which has the
thread on the inside) has a cone-shaped end that
away from the end where
it meets the male nut (which has its thread on the outside).
Metric female nuts, on the other hand, are hexagonal in cross section almost
from one end to the other, and have just a small circular section at. one end
to hold the flare of the brake pipe.
There are also visible differences between metric and imperial male nuts.
Imperial nuts are threaded all the way up to the hexagon head, whereas metric
nuts have a shorter length of thread which stops short of the head.
Types of brake pipe flares
There are two types of flare you may come across when renewing brake
pipes: single and double.
Before you start work, decide whether you need to keep the old pipes as a
guide for shaping the new ones. If your new pipes are a ready-shaped set from
your dealer, then you don't need to do this, so you can cut or bend the old
pipes if necessary when removing them.
On the other hand, if you have bought unshaped lengths of new pipe and plan
to bend them into shape yourself (see sideline overleaf for how to do this),
you should try to keep the old pipes intact.
Next, examine the pipe you intend to replace to find out if there is a hose
at its reservoir end that you can clamp to hold the fluid in the system. If
there is, clamp the hose, then take the cap off the brake fluid reservoir,
place a plastic bag over the reservoir top and replace the cap. This will keep
the loss of brake fluid to a minimum when you take out the old• pipe.
If there is no suitable hose you can clamp, and the section of pipe you plan
to replace connects directly to the brake fluid reservoir, you should first
drain the system of fluid. Take the cap off the reservoir and open the
nipple on one of the brakes (any brake if the braking system is single
but if the system is dual circuit open one of the nipples on the appropriate
half of the system). Have a container ready to catch the fluid and
brake pedal to
the fluid out.
Removing a damaged pipe
Having first drained the braking system of fluid, undo the union where
the pipe leads into the brake
Then undo the pipe where it joins its brake hose (2). Finally,
disconnect the pipe from its retaining clips (3) and remove it.
Removing old pipe
How you undo the union at each end of the pipe depends on what that end of
the pipe connects to. If it connects to the reservoir or the brake itself, you
can simply undo the union with a spanner. If the union is corroded, you may
need to use penetrating fluid on it.
If it still won't shift, cut through the pipe with a hacksaw to allow you to
get a ring spanner or slip-joint pliers round the union. Alternatively use a
special split-ring union spanner (see sideline overleaf). This will give you
If the pipe is joined to a brake hose, you will need two spanners one to
undo the union and another on the metal end of the hose to hold it steady,
otherwise the hose will simply turn with the pipe as you try to undo the
After undoing the pipe unions,
openings left in the system with a small
plastic bag tied firmly round the opening. This will prevent any dirt entering
the system and stopping the brakes from working properly.
The pipe will probably be held to the car's underside or to components by
metal tags or plastic clips. These prevent the pipe from flexing too much or
knocking against other parts and getting damaged. Pull the pipe free (bend back
a metal-tag type first), taking care not to bend it. If any of the plastic
clips break, make sure you get new ones to
with the new pipe.
Fit new pipe
If you bought an unshaped section of pipe, you need to bend it to match the
shape of the old pipe.
First work the pipe roughly into position, passing it through any bulkheads
or around obstructions. Then, starting at one end, screw the union on the end
of the pipe into the union on the hose, reservoir or
. Do the union up
finger-tight only, then attach the union at the other end in the same way. Once
both unions are engaged, tighten them up with a spanner.
Now fasten the pipe to the underside of the car, routing it into the
securing clips. You may need to bend it a little for a good fit. Make a final
check that the new pipe cannot come into contact with any moving parts such as
the prop shaft.
Finally, bleed the braking system, then get a friend to press hard on the
brake pedal while you check the unions to make sure there are no signs of leaks
in the system.
Flaring your own brake pipes
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As well as being a legal requirement, it is also an essential safety measure that your brake lights work correctly. Any faults in the brake lights are usually easily traced. The circuit itself is a simple one, controlled by a switch operated either directly by the brake pedal or hydraulically by the increase in pressure in the brake pipes.
The fluid in the car's braking system runs from the master cylinder to the
brakes themselves mainly via rigid metal pipes. But there needs to be some
flexibility in the system to allow the wheels to move in relation to the car
body, whether for the purposes of steering or suspension. This is provided by
fitting flexible brake hoses.