Back to basics with brake service

March 6, 2024
Though a brake job isn't anything new for most technicians, it's those everyday tasks that you run the risk of forming bad habits.

There's not much I can tell you guys about performing a basic brake job that you don't already know. We've all done it a thousand times. The thing is, a thousand brake jobs create a thousand opportunities to develop some bad habits. So what do you say we review elemental disc brake job etiquette? 
                           

Road test and visual inspection

It's crucial to know if there are any brake-related symptoms before putting the vehicle up on the lift. Look for brake noise, pulsation, and a low brake pedal during your road test. A brake pulsation that causes the steering wheel to shimmy originates from the front brakes. If you feel the pulsation in the seat, it's coming from the rear. This way, you know what to look for during the visual inspection. 
If you feel a front brake pulsation, before pulling the wheels, shake the front suspension. Loose steering and suspension components can cause the steering wheel to shimmy when braking, causing a misdiagnosis. 

The first step of the brake system visual inspection is to pull the wheels. I use a Matco Tools 1/2" High Torque 20V Impact Wrench to remove the lug nuts; lots of torque, no air hose. When removing lug nuts on custom wheels, I use Sunex Tools Custom Wheel Sockets to protect the finish (Figure 1). 

There are plenty of types of gauges to measure brake pad lining thickness. I like using the OTC 6596 Brake Pad Gauge because it gives an accurate measurement and, in some cases, allows the technician to measure the outboard brake pad without removing the wheel (Figure 2). 

A careful inspection of the rotor is essential. Choppy lines that extend from the hub to the edge of the rotor indicate a pulsation, as does an uneven wear pattern around the face of the rotor. High ridges along the inside and outside edges are noise makers. The rotor thickness should be measured and referenced against specs to verify there is enough room to remove the ridges. I use my Central Tools micrometer to determine rotor thickness (Figure 3). Figure 4 shows a rotor that we measured to determine runout before machining. As you can see, this one is within specs.

Disassembly

Most brake calipers are attached to the knuckle or axle with a bracket. As you know, removing both components as an assembly is possible. If you plan to replace the brake pads, this is a bad idea because you need to access the slide pins. I use a Milwaukee Tool 3/8" drive 12V battery-powered ratchet to remove the caliper to bracket hardware. You can see how old and beat up my Milwaukee ratchet is by looking at Figure 5. Sometimes, the caliper slides are integral to the hardware, but others are separate. I use my 1/2" impact to remove the bracket bolts and the bracket. This is a good time to check the caliper piston for leakage. Any dampness around the piston dust boot is bad.

We've all had to deal with rotors that are frozen to the face of the hub. Do not hit the rotor with a hammer. Even hitting the hub portion of the rotor, between the wheel studs, can cause rotor warpage. The best way to remove stuck-on rotors is with an air hammer. I use a Chicago Pneumatic Air Hammer that delivers 1,800 blows per minute. Using a smoothing hammer bit, go around the rotor, hammering between the wheel studs. This breaks the rust seal and loosens the rotor without causing damage. 
                               

Resurfacing brake rotors

I am a big fan of the on-car brake lathe. The on-car brake lathe resurfaces the rotor on the hub, eliminating the need to remove the rotor, and producing a more accurate rotor surface. We use a Pro-Cut PFM 9.2 on-car brake lathe. You can see in Figure 6 that the on-car setup is quick and straightforward. The industry standard states that up to a 0.015" cut is acceptable per pass, per side, whether you choose to use an on-car or a standard brake lathe. I think 0.015" per cut is too much. You'll find that you'll get a much cleaner cut if you keep it under 0.010" per cut. Remove the ridges before making the first pass, and measure the rotor thickness when finished.
                                 

Retracting the caliper piston

Retracting the caliper piston is not as simple as pushing the caliper back with a large pair of pliers. The fluid behind the caliper forces fluid back into the master cylinder reservoir. This creates a problem if there isn't room in the reservoir for the backflow of fluid and a spill of corrosive brake fluid if the reservoir cap is removed. This is why it's advised to open the bleeder screw before retracting the piston. There's also another reason to open the bleeder screw. I'm sure you've noticed the color of the initial fluid that comes out when bleeding a brake caliper. The brake fluid that resides in the caliper can easily reach temperatures of over 200 degrees F. Pushing that fluid out of the system when performing a brake service is advisable.
 

Using pliers in place of the proper tool can cause the piston to slant when retracting, damaging the caliper piston seal. The Orion Motor Tech Tools caliper retraction tool is an excellent, inexpensive tool for front and rear calipers. Figure 7 shows how the tool fits into the grooves on the rear caliper piston, allowing for easy piston retraction. A screw-type retracting tool allows the technician to feel the resistance as the piston slides back into the caliper. There should be minimal resistance with the bleeder screw open. 

Rear calipers with integral parking brakes retract by turning the piston onto the actuator screw. Most turn clockwise, but be careful; some models retract counter-clockwise, and turning the piston in the wrong direction can damage the caliper. Rear calipers with integral electric parking brakes must enter service mode before disassembly. Reference the service manual.
                                                   

Assembly 

After the pistons are retracted and the rotors are resurfaced, it is time to assemble the brakes. Compare the brake pads to the originals. Look for any discrepancies in the design. Some brake pads have small alignment pins on the back. Ensure the pads you are installing have the pins in the same location. Sometimes, inboard and outboard pads are determined by the location of these pins. Rear calipers with an integral parking brake use these pins to align the pad to the machined opening on the caliper piston. Be sure to align these pins with the caliper. Depending on the manufacturer, there are many differences between inboard and outboard brake pads. Scrutinize the pads before installation.

Improper installation can cause a brake squeak. Customers hate to hear noises coming from their newly purchased brake job. Proper lubrication is the first step to prevent brake noise. I use Motorcraft Caliper Slide Grease. This is a silicone-based lubricant that works great to lube the friction points on the caliper. Apply lube where the caliper and the caliper bracket meet. Also, lube the pads where they contact the caliper. If the caliper uses removable pins, lube the pins before installation. Don't over-apply the grease. Too much lube attracts road debris that can lead to brake noise.

Brake noise can also emanate from the friction between the back of the brake pad and the caliper piston. Some new brake pads come with a tacky substance already applied to the brake pad. When that's not the case, I apply CRC Disc Brake Quiet to the back of the pads to prevent brake squeaks. 

Be sure to torque all brake hardware and lug nuts. Too tight can cause just as many problems as too loose. My Mac Tools 1/2" drive torque wrench has a flexible head that makes it easy to get at the caliper bolts behind the steering knuckle. 

After assembly, road test the vehicle as the customer would on their way to Walmart. No need to "ride the brakes to break them in." No noise, with a good solid pedal, means a good solid brake job. 

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