YOU ARE IN CONTROL WITH OUR TECHNICAL TIPS
Light vehicles
Find out the different types of judder, its causes and solutions. Here's your complete checklist.
Brake judder is the vibration felt through the steering wheel and suspension when the brakes are applied at certain speeds and pressures. It can vary from a barely noticeable vibration to a violent judder – experienced either through the brake pedal or steering wheel.
CAUSES AND SOLUTIONS
CAUSE 1: HUB AND/OR DISC RUN-OUT
Brake judder can be caused by a badly fitted brake disc pulling out of alignment with the hub or caliper. To help you identify if this is the case, here are some symptoms and solutions:
Check for rust or dirt on the wheel hub
surface
WHY? Rust
or dirt causes poor contact between the disc
and hub.
THE
SOLUTION: Dismantle
the disc and clean both surfaces to remove
rust and other pollutants.
Check whether the hub contact surface has
been distorted by excessive tightening
torque
WHY? Using
overly severe tightening torque on the
positioning screw leads to vibrations
throughout brake application.
THE
SOLUTION: Replace
the discs, avoiding excessive tightening
torque.
Check for distortion of the hub itself
WHY? Although
rare, it's possible for hubs to warp.
Bolting a disc to a warped hub will always
result in brake vibration. The same will
happen if any rust from the hub surface is
not removed before fitting the disc.
THE
SOLUTION: After
fitting a disc, always check for disc
run-out using a dial gauge. If the run-out
is out of tolerance, re-fit the disc in an
alternative position until the run-out is
within tolerance. If run-out still remains
out of tolerance, hub maintenance is
required.
Check whether the alloy wheels have been
fitted correctly
WHY? A
common cause of disc run-out in recent years
is the incorrect fitment of
‘one-size-fits-all' alloy wheels. As the
same wheel is used for multiple hub types
and sizes, installers are using location
spacers on the wheel spigots. If the spacer
is lost or damaged, the wheel cannot be
correctly centred.
THE
SOLUTION: Place
the run-out gauge on the back of the disc
while fitting the wheel, and measure the
run-out. The gauge will only show run-out
once the wheel is fitted and tightened, and
it may be necessary to change the wheel.
CAUSE 2: SEVERE DISC OVERHEATING & DISTORTION
Any severe temperature increase can cause the disc metal to distort in different areas of the disc. These ‘hot spots' cause intermittent contact between the pad and disc. And that results in judder. To help you identify if this is the case, here are some symptoms and solutions:
Check for any signs of brake abuse
WHY? Brake
abuse is the most common reason for
overheating. Discs are designed to cool
rapidly between brake applications. But when
the brakes are applied intensely in quick
succession – e.g. during alpine driving –
the discs don't get enough time to dissipate
the heat.
THE
SOLUTION: Blue
spots on the disc surface are a good
indication of overheating. Discs that show
blue spots and/or a darker colour in some
areas cannot recover and should ALWAYS be
replaced, together with the brake pads.
Check the quality of the brake pads
WHY? Poor
quality brake pads can overheat very easily,
especially during heavy braking. The
excessive heat from the pads can cause the
discs to overheat, resulting in disc
warping.
THE
SOLUTION: Again,
look for blue spots on the disc surface.
When you can't find any, inform the driver
of the risks of poor quality pads. ALWAYS
replace the brake pads and discs when you do
see blue spots on the disc.
CAUSE 3: DISC THICKNESS VARIATION (DTV)
DTV is the variation in thickness around the disc surface. For effective braking, the disc should have the same thickness throughout. If there is an uneven friction surface, the brake pad loses and regains contact with the disc(s) as it turns. And that's what causes brake judder. To help you identify if this is the case, here are some symptoms and solutions:
Check with the driver to see if the
brakes have been properly bedded in
WHY? To
get the best performance from your
brakes, it's essential to follow the
bedding-in procedure. By applying only
moderate pressure on the brake pedal
during the first few applications, an
even layer of friction material is
transferred from the pads to the disc.
Mating the surfaces this way improves
safety and prevents DTV-related judder..
THE
SOLUTION: Prevention
is better than cure. Each time you fit
new brake pads, inform drivers that they
should avoid hard braking for the first
200 km. When poor bedding-in has
resulted in slight DTV, it may be
sufficient to bed in the brakes once
again. If this does not re-align the
disc surfaces, the only solution is to
replace both the brake pads and discs.
For your convenience, OEFILIS has
published a useful Driver Tips leaflet
for you to hand to your customers. It
includes a few tips and tricks to
optimise their brake systems. Ask
your OEFILIS representative for more
information.
Check for caliper seizure
WHY? A
seized caliper piston, or a seized
caliper sliding pin leads to uneven
forces being applied to each side of the
brake disc, creating uneven wear – or
DTV.
THE
SOLUTION: This
problem is usually caused by corrosion
or dirt. Therefore, run the proper
maintenance of the seized caliper to
prevent the problem from recurring, and
replace both the brake pads and discs.
Check for dirt or corrosion on the disc
surface
WHY? During
braking, some of the brake pad's
friction material transfers to the disc.
But with poorer quality brake pads, the
deposits of friction material can stick
to the disc unevenly, changing the
disc's thickness and parallelism.
THE
SOLUTION: If
there's only minimal DTV, it may be
sufficient to remove the deposits using
a brush or sandpaper and road test the
brakes. If this has not re-aligned the
surfaces, the only solution is to
replace the pads and discs.
Check for pad imprints on the discs
WHY? Holding
the brake pedal depressed when the
brakes are overheated may imprint or
weld pad material on to the discs. The
DTV will often be visible as the outline
of a brake pad on the disc surface.
THE
SOLUTION: It
should normally be sufficient to remove
the pad imprint using a brush or sanding
paper.
© Copyright 2015 OEFILIS Brake System.