When to replace your brake rotors

Your vehicles brake
system

The brake system consists of three main parts: the brake
pads, rotors and calipers.  The pads are
generally made from a friction material like composite to ceramic, to metallic
with a steel backing plate.  Rotors can
be made of ceramic matrix composites, reinforced carbon on carbon or just cast
iron, and are attached to the wheel or axle. 

When you push your brakes, brake fluid rushes in to engage a
piston that clamps each brake pad on to the rotor. 

What is a rotor?

Brake rotors are also called discs, and are an important
component of your braking system.  It’s
what your brake pads apply pressure on to stop your wheels from spinning.  They are just as important as brake pads, and
though they last longer than brake pads, they should be inspected
regularly.  Rotors are regularly subject
to heat that wears them out and causes deforming. 

What are rotors made
of?

Rotors are usually made of cast iron, but some are made of
composite metals like carbon or ceramic matrix composite metals. There are many
kinds available.  Higher quality zinc
coated rotors that fight off surface rust.

How does a car rotor
work? 

There are three types of brake rotors: smooth, drilled and
slotted.  A drilled rotor is full of holes,
and though this may not make much intuitive sense at first, since there is less
surface area available for the brake pads to grab a hold of, however, there are
three reasons why holes in a rotor makes sense: heat, gas buildup and water.

When a brake pad grabs a rotor, it creates friction, which
in turn creates heat.  The heat causes
brake fade, which decreases stopping performance. Have you ever ridden your
bike down a long hill? You probably notice after awhile your brakes not feel as
touchy as before. This is because heat builds up and can’t escape fast enough.
Gas buildup isn’t as big of a problem as it used to be with older materials.
This happened when older types of brake pads caused a gas buildup between
rotors and pads, and this gas limited stopping power. 

A wet rotor is slippery and difficult for the brake pad to
grab.  If the rotors get wet, such as if
you drive through a puddle or are driving through rain, your brakes won’t be as
effective. So when you drill holes into the rotor, it allows all these
elements: heat, gas and water to escape and improving brake performance.

Types of Rotors

There are three main
types of rotors, and variations on those in between. They are smooth,
slotted and drilled brake rotors.

There are three main
types of brake rotors.  Image from
3sx.com

1.  Smooth Brake Rotors

A good quality set of smooth rotors gives plenty of great
stopping power on most vehicles. In fact, it’s still used on over 99% of new
cars today.  The smooth surface provides
more surface area for stopping power and are effective as acting as a heat
sink. Trapping heat is in fact, what rotors were designed to do in the first
place.  They are much less prone to
cracking than drilled rotors and can handle extreme braking conditions better.

The absence of surface anomalies allows them to maintain stronger
structural integrity than the other types of rotors.  This makes them good for moderate track use
when used with high performance brake pads and high boiling point brake
fluid.  Brake fluid is subject to very
high temperatures, especially in the cylinders of brake calipers, and it needs
to be able to withstand these temperatures so it doesn’t vaporize in the lines.
Track driving means a lot of braking and a lot of heat generated by the brakes.

2. Slotted brake
rotors

 Slotted brake rotors don’t have holes, but have slots that
are carved at and angle on the rotor, which directs heat, water and gas away
from the rotor surface.  These types of
rotors are popular with performance cars because they subject their rotors to a
lot of stress, and drilled rotors are more prone to developing cracks with
heavy and repeated use.  In general,
since they are more durable than slotted brake rotors, they are a better choice
for some performance drivers.

 Slotted rotors are great for
high performance driving.  Image from
auto.howstuffworks.com

The disadvantage of these is they wear out brake pads
quickly due to their irregular surface. 
Because they wear out so fast, most rotors on every day performance cars
tend to be drilled instead of slotted. 
While drilled is too weak for racing, performance vehicles can use them
on street cars for general driving and save the slotted rotors for the race
track.

These grooves are cut where the pad makes contact with the
rotor.  The venting provided by slotted
rotors is one of the best ways to fight brake fade and have consistent stopping
power.  Slotted rotors have better brake
‘bite’ because the gases generated during friction are allowed to dissipate and
actually allow the brake pad to have more contact with the rotor as a result.

Most of the time, the slots are grooved with a smooth edge,
but some dedicated ‘racing’ rotors will have sharp grooves, which give better
braking, but can speed up brake pad wear.

Slotted have become the main choice for performance driving.

3. Drilled Rotors 

As mentioned above, drilled rotors are great at keeping the
rotor cooled under heavy braking. They also look pretty great behind a set of
flashy wheels.  When they were invented,
they were mainly used by race cars as they were great at venting the layer of
gas and dust that built up under heavy braking.  But brakes have come a long way, and brake
pads are much better, and gassing is less of an issue.  You won’t see drilled rotors anymore on any
modern race car.

 Drilled slotted brake rotors. Image
from: RyebreadPics on Flickr.

For regular street driving, your brakes don’t come close to those that
you would see on the race track, and so the venting properties of drilled
rotors coupled with improved wet weather performance work well for keeping the
temperature of the brake system down and extending the life of your brake
pads.  For drilled rotors, cross drilled
are the best choice due to the pattered grooves that direct moisture and heat
to the outside of the wheel.

Drill slotted Rotors

You can also get drill slotted rotors, which have the
advantages and disadvantages of both types. As you can see, the holes are
directed in a pattern that encourages moisture and heat to dissipate to the
outside of the wheel, and has slots to channel it.

These are not ideal for heavy racetrack braking, they are
great for heavy vehicles towing heavy loads. 
Heavy vehicles need more energy to slow them, and their brake systems
are subject to high heat.  These rotors,
because they run cooler can provide better security.  These rotors will keep the rotor temperature
down and the rotor surface clean.    

Drilled and slotted brake
rotors on a high performance vehicle. Image from Blake Ramick via Flickr.

It’s important to note that slotted or cross drilled rotors
won’t decrease your vehicles stopping distance. 
For regular, every day driving, any of the rotor choices will work well.

Servicing your brakes

Brake pads can be replaced when your rotor is replaced.  To get new pads and rotors, you can expect to
pay:

Rotors: $30-75 per rotor

Pads: $35-150

Labour: $150-200

Total $250-500 per axle 

Generally, brake pads should be replaced between
50,000-150,000 kilometers for semi metallic pads. 

Factors that affect
the cost 

·     
The year, make and model of your vehicle

·     
Whether you do it yourself, take it to an
independent mechanic or dealership

·     
Brand and quality of the brake pads and rotors
used

·     
The shops hourly labour charge, where cities
will be more expensive than smaller towns

DIY or Mechanic?

The primary cost will come from whether you purchase the parts
and do it yourself or have a
professional mechanic do the work for you. 
Having brakes replaced by a mechanic will cost more than doing it
yourself, but it’s not a simple or quick job unless you know what you are doing.
 Replacing brake pads is a simple process
but replacing the rotors is much more challenging and requires some special
tools, and you should leave it to the professionals unless you are confident of
your automotive mechanic skills.  You
will have to buy specialized tools and won’t save you money in the long
run. 

Quality of parts

Brake pads come in a wide range of quality levels and
materials and the quality is reflected in the price.  Premium ceramic pads will cost more than
those standard semi metallic pads.  Do
some research to find out what pads you should get for your specific driving
needs.  Do you spend a lot of time on the
highway or is most of your driving in the city in inclement weather? 

How do you know when
you need to replace the rotor or disc? 

You know it’s time to replace your rotors when you feel
vibration or pulsing when you apply the brakes and a blue discoloration of the
rotor surface.  Grooves or hot spots form
on rotors and cause this pulsation. Don’t even bother getting them machined at
this point, simply get them replaced.

Brake rotor
resurfacing or machining

Brake rotors are among the most replaced parts on your
vehicle.  Sometimes, you’ll be able to get
your rotors machined, or resurfaced, instead of replaced, saving you a little
money.  To machine a rotor, a mechanic
uses a lathe to grind down the rotors to make them smooth to get you some more
mileage before replacing them. 

Most mechanics recommend an on wheel lathe for resurfacing.
These are quicker and more accurate.

Considering the difference between machining the rotor and replacing
it is only around $50 thanks to the price of rotors going down, machining your
rotors doesn’t always make sense. If you feel heavy pulsation through the gas
pedal, your rotors are not effective and should be replaced. 

How to replace brake
rotors 

Is this something that you can do yourself? You need to be confident
of your automotive skills to do this. 
It’s not as simple as changing
spark plugs or your car
battery.  You’ll need special tools
which not may be worth the investment if you are only performing this job once
in awhile.  Here is a general overview of
what the process looks like.

Brake rotors are replaced by jacking the car or truck up on
a lift.  The wheel is removed to provide
access to the rotors. To do this, the lug nuts, the nuts that hold the wheel to
the vehicle, are removed. Then the calipers are removed. These are usually held
in place by one or two bolts that screw in from each side.  

The caliper is usually not disconnected from the brake line,
 if they are, the brakes will begin to
bled out brake fluid, and will need to be bled after the repairs.  Mechanics will also not let it dangle freely
as this can damage the brake hose and instead hook it in some fashion to the
undercarriage to keep it in place.

He caliper mounting bracket bolts are removed and finally
the rotor itself.  Sometimes it will
slide off the wheel hub easily but if it hasn’t been replaced in awhile, it may
be rusted and be difficult to remove.  

After the new rotors are put on, a C-clamp is used to
compress the caliper pistons.  The
caliper should fit over the rotor when the pistons are completely
compressed.  After the wheels are
installed, the rotor is tested before driving. This is done to ensure
everything works before driving away. 
The brake pedal is depressed, and when the job is well done, will come
up slowly.  The brakes are pumped a few
times and there should be no squeaking or vibrations.  

If you have any concerns about rotors you should always ask
with your service
advisor.

Further Reading

GMPartsNow.com  ‘Brake
rotor resurfacing’  howto.gmpartsnow.com/brake-rotor-resurfacing-vs-replacing-what-exactly-can-i-get-away-with/

How Stuff Works – Auto ‘How brake rotors work’ auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-rotors3.htm 

Brake pads cost guide www.brakepadscostguide.com

Auto Anything.com Drilled or Slotted Rotors www.autoanything.com/brakes/drilled-or-slotted-rotors-what-are-the-best-brake-rotors.aspx

Brake pads cost guide www.brakepadscostguide.com