Replacing Disc Brakes — Five Pro Tips

Unlike working on drum brakes, replacing disc brakes isn’t very complicated. There are fewer parts, but it’s also worth noting that each part is more important, especially when front disc brakes account for upward of 70 percent of vehicle braking and stability. In talking with technicians over the years, after hundreds of disc brake jobs, we’ve collected five pro tips to make replacing disc brakes easier. Here’s what the professionals have to say.

1. Bleed the Calipers

One of the first steps to replace brake pads is to compress the brake caliper piston, and the easiest way is with a small pry bar or caliper piston tool. Note that if you are working on rear disc brakes you may need a special tool that both compresses and rotates the caliper piston at the same time. Before compressing the piston though, pinch off the flexible brake line with the proper tool (do NOT use generic locking pliers as damage to the brake hose is possible) and open the brake bleeder screw. Now compressing the caliper piston will force the most-abused brake fluid out of the system instead of pushing it back to the master cylinder. Just remember to top off the master cylinder with new brake fluid later.

2. Ensure Everything Moves Freely

Depending on the disc brake design, the brake caliper may move, and the brake pads need to move with it. On assembly, if the brake pads don’t slide freely on the pins, carrier or caliper, they’ll drag on the brake rotor causing premature wear or cause braking pressure to be applied unevenly. If necessary, use a wire brush, powered wire wheel or if necessary hammer and chisel to remove rust scale. Paint over any bare metal to prevent corrosion from building up again, allow it to dry and then reassemble.

3. Hold the Rotor

Some brake rotors are held onto the wheel hub or axle by screws, but not all. In the absence of screws to hold it you can use a wheel lug nut to keep the rotor from flopping around. This will make assembly easier. Make sure to check the kind of lug nuts first. If you have plain open ended acorn lug nuts just thread it on as usual. If you have closed end lug nuts double check that the wheel stud does not bottom out in the lug nut, as damage to the lug nut itself could occur. You can always slide on the brake rotor and stack a few washer on the wheel stud to take up the slack. Regardless just remember this is temporary so the lug nuts only needs to be finger tight.

4. Use the Right Lube

The right lubricant can save several headaches, either yours or the mechanic’s. Use the right lube in the right place to keep things moving without causing future problems. Lubricant should be used sparingly, so don’t glob it on. Here’s a brief guide on what to use (or not use) and where:

• Anti Seize: The only place to sparingly use anti seize lubricant is on the brake rotor center hole, where it rides on the wheel hub. On caliper slides, it will dry out and seize up, but not before destroying the rubber boots.
• Heavy silicone grease: Caliper slides and pins should be lubricated with heavy silicone grease or rubber-compatible brake lubricant. Just make sure the caliper slides are nice and clean before lubing them up. Same goes for the pins.
• No lubricant: Brake pads are installed dry, with no lubricant on the areas where the pad retaining pins or slides contact. Still, a small amount of anti seize on the threads only (not the shaft) will prevent the pins from seizing in the caliper body.

After assembly, put on safety glasses then use brake cleaner and a rag to prevent contamination of the brake pad linings and the brake rotor.

5. Check the Rotor Runout!

When replacing brake rotors, check and adjust for rotor runout. Excessive brake rotor runout can cause vibration during braking and accelerate wear on steering and suspension components. Brake rotor runout should ideally be 0″, but 0.002″ or 0.003″ (2 or 3 thousandths of an inch) is the maximum acceptable amount. Major runout may be caused by defective rotors or wheel hub damage, but rotor “clocking” can usually minimize minor runout. But first make sure the wheel hub is absolutely clean of any rust or dirt. A crusty wheel hub can prevent the rotor from seating fully. Take the time to grab a wire brush to clean not just the flat hub surface but also the wheel studs and the center hub. Once everything is clean you can remount the rotor and check for runout.

A dial indicator can save time and frustration chasing problems after replacing disc brakes. With the dial gauge contacting the rotor 1/4″ from the edge, turn the rotor slowly through 360°. Use a marker to mark the highest spot on the rotor and the closest wheel stud. Remove the rotor and replace it approximately 180° from the marked wheel stud. If this doesn’t minimize runout, you may have a defective rotor.

It’s true that the professionals replace disc brakes all the time, multiple times per day, even, but that doesn’t mean that you can’t benefit from their experience when doing the job at home. If you get stuck, it’s best to stop and call your local NAPA AutoCare locations for expert help.

Check out all the brake system products available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on replacing disc brakes, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Wikimedia Commons.