Practical Automotive Maintenance: Brake Pad Replacement

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Brake Pad Replacement

07.06

00:00	In this module we're going to run through the process of changing brake rotors step by step.
00:04	Before we begin though, it's worth understanding when and why rotors need replacing.
00:08	Brake rotors wear out over time just like pads and with traditional iron rotors, the primary factor determining their service life is the thickness of the friction area.
00:17	Brake manufacturers will define a minimum thickness for this area, usually identified by an engraving on the rotor hat or the outer ring of the rotor.
00:25	This indicates a non-negotiable replacement thickness.
00:28	And breaching this can negatively affect braking distances as well as cause the rotor to suffer from warping thanks to the reduction in material and therefore a lesser heat threshold.
00:39	This measurement is easily carried out using a set of basic vernier calipers to gauge the thickness of the rotor on or off the car.
00:46	Another indication of worn or excessively thin rotors is easily visualised by a lip or step developing on the very outside edge of the rotor face, caused by the gradual wearing down of the contact surface by the pad.
00:59	Other situations where replacement of the rotor should be considered, or even necessary, are when the friction surface becomes warped.
01:06	Meaning the rotor has high and low spots, generally caused by heat soak, isolated to one area more than another.
01:12	This is generally going to be very easy to notice while driving as under heavy braking, the vehicle will shudder or shake.
01:18	We can further pinpoint at which end the problem rotor is, by whether it's the steering wheel that's shaking or the body of the car.
01:25	If it's the wheel, it's most likely going to be at the front end, and if it's the body, it'll likely be at the rear.
01:31	More advanced motorsport materials like carbon and carbon ceramic also have minimum weight limits, requiring careful monitoring, but for most road cars, thickness, condition and the feel under braking are the deciding factors.
01:43	Before we get started, it's important to note that if we're replacing rotors, we need to be replacing pads at the same time, as we shouldn't run used pads on fresh rotors.
01:52	We can, however, use fresh pads on used rotors, so with that in mind, you'll find the pad changing process in a separate module coming up next.
02:01	OK, let's take a look at the process of replacing rotors.
02:04	To get started, we need to make sure that we have the correct replacement rotors, brake clean, a torque wrench, breaker bar, sockets and wrenches, and a wire brush, as well as some penetrating oil and anti-seize.
02:15	If the car has an electronic parking brake, we need to ensure that it has been put in service mode before we begin, using the manufacturer's procedure or a scan tool.
02:24	Let's start by lifting the car securely, either on a hoist or with a jack and axle stand, and removing the wheels.
02:30	If we're only replacing the front or rear rotors, we can just lift that end, but it's always important to chock the wheels left on the ground, so the car can't roll.
02:38	Before the rotor can come off, the brake caliper and its bracket need to be removed.
02:42	It's always a good idea to take note of the routing of any sensor wiring at this point, so we can make sure it all goes back on the same way once we're done.
02:50	Unbolt the guide pin or caliper bolts, and then support the caliper with a cable tie, so it doesn't hang from the hose.
02:56	Next, we can remove the caliper bracket by undoing the large bracket bolts.
03:00	These are often very tight, so a breaker bar or impact tool will help.
03:04	With the caliper and the bracket out of the way, we can now remove the rotor.
03:07	Some rotors have small set screws securing them to the hub.
03:10	So, spray these with penetrating oil and loosen them carefully, ideally using an impact driver to avoid stripping.
03:17	If the rotor is rusted to the hub, use a couple of bolts in the threaded jacking holes if present, tightening them alternately to push the rotor off.
03:25	Otherwise, a few gentle taps with a plastic mallet will usually break the rust bond.
03:29	For rear rotors with a drum style parking brake built into the hat, it's always best to loosen the handbrake shoes by adjusting the star wheel to make the removal easier and avoid damage.
03:39	Once the rotor is off, wire brush the hub face to remove any sign of dirt and corrosion and wipe it with brake clean.
03:45	Be careful not to remove too much material with abrasives.
03:48	The goal is clean, flat metal, not thinning the hub surface.
03:52	It's always a good idea to apply a thin layer of anti-seize on the hub face to help prevent future rust bonding.
03:58	For two piece rotors, we can separate and replace the friction ring on the bench, checking that the centre hat is still in good condition before reassembly.
04:05	Before fitting a new rotor, always remove the protective oil coating with brake clean until the friction surfaces are completely residue free, as oil contamination will seriously compromise braking performance and can ruin pads.
04:18	Sliding the replacement rotor onto the studs, temporarily secure it with a set screw or a couple of finger tight lug nuts to hold it flush against the hub.
04:27	It's also important to check the orientation.
04:29	Some rotors, especially those with curved vanes, and must be fitted to the correct side of the vehicle.
04:35	So, look for a L or R marking or arrows showing the intended rotation.
04:40	If no direction is specified, then orientation isn't critical and the rotor can be fitted on either side of the vehicle.
04:46	With the new rotor in place, the caliper bracket can be reinstalled and its bolts torqued to specification.
04:52	Then the caliper, complete with new pads, can be fitted back over the rotor and the bolts torqued correctly, making sure the rubber boots on the pins are seated properly.
05:00	Again, we'll be tackling the pad replacement process in detail in the following module and even though it seems like a simple job, there's still plenty to learn, so it's well worth checking out.
05:10	One thing to note at this point is that if our old rotors were severely worn, there's a good chance we may have to retract the caliper pistons in order for the caliper and new pads to fit back over the new rotor as it'll be considerably thicker.
05:22	If this is the case, the procedure for correctly retracting caliper pistons is covered in the following module which covers the process of changing brake pads.
05:31	We can now repeat the process on the remaining corners of the car.
05:34	With all rotors installed, if we have a drum handbrake, we can reset the adjustment and then remove any fingerprints or residue from the friction surfaces with brake cleaner.
05:43	It's now time to refit the wheels, snug the lug nuts in a star pattern, lower the car and torque the nuts to the factory specifications.
05:50	On cars with electronic parking brakes, remember to disable service mode before finishing the job.
05:55	After a short test drive, inspect each corner for leaks, rub marks or loose hardware and always recheck the lug nut torque once the wheels have cooled.
06:04	This completes our test drive.