| ABS Disc Brakes -- Front-Brakes Servicing |
From "Weekend Mechanic"
episode WKM-202 |
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ABS Disc Brakes -- Front-Brakes Servicing With the brakes disassembled, and the rotors re-machined, work can begin putting the front brakes back together. Important: Included below are the steps in this automotive procedure as shown in the episode. These steps are general guidelines that are applicable to most vehicles. With any particular vehicle, there may be procedures, specifications, settings, tolerances, components, etc. that are specific to that vehicle. There are also variations according to the type and brand of repair kit you select. Always consult your vehicle's service manual when undertaking significant automotive repairs, and read and follow the manufacturer's directions and precautions that come with your kit or replacement parts. Safety Alert: Always wear eye protection, and follow proper safety precautions, when working with power tools. Safety Alert: As a standard safety precaution, always disconnect the vehicle's negative battery cable before you begin work on any electrical or mechanical components.
- Before installing the replacement front-wheel speed sensor, make sure that the mounting surface and hole for the sensor (figure A) are clean. Use a clean rag and a wire brush to clean the surface (figure B). This is critical since the gap between the sensor and the toothed wheel is 20/1000th of an inch, and is non-adjustable. Any debris could alter the gap, and interfere with the signal that's sent to the brake-system computer.
- Before installation, apply a small amount of anti-seize compound to the sensor (figure C). Without the application of this compound, it would be very difficult to remove the sensor later, if that's necessary.
- Position the sensor in it's hole, an install the mounting bolt to secure it ( figure D).
- Route the sensor harness and plug it into the connection, connecting it just as it was with the old sensor. Check your vehicle service manual if you are unsure of the routing procedure.
- Before mounting the caliper or disc pads, check the caliper-mounting hardware. If any of the parts are ripped or worn out, they should be replaced. In this case, a ripped bellows (figure E) was replaced with a new one.
- Remove the rubber bellows to expose the outer bushings. Use a screwdriver to carefully pry out the outer bushing (figure F).
- To remove the rubber bushings from inside the housing, you may want to fashion a small hooking tool out of wire (figure G).
- With the old inner bushing removed, replace it with a new one (figure H). Then, use a socket and a plastic hammer to tap the outer bushing into place. Don't install the bushing flush with the caliper housing. Leave a gap of about 1/32-inch for the lip of the bellow to slip onto.
- Work the lip of the bellow around the bushing.
- To help maintain the bracket, lubricate the areas where the brake pads will rest. This prevents the pad from wearing into the bracket. Specialized caliper grease is available at auto stores, and is formulated to withstand high temperatures.
- Before reinstalling the newly resurfaced rotors, clean the hub of the drive axle using a wire brush (figure I). This will help ensure proper operation when the brakes are reassembled.
- Position and install the re-surfaced rotor on the hub.
- With the rotor in place, the caliper-mount bracket can be installed. Before installing it, apply a small amount of lock-tite on the threads of the bracket's mounting bolts (figure J).
- Install the bracket, snugging down the bolts by hand (figure K), then come back and torque-tighten the bolts to the proper specs.
- Next, the caliper can be installed. As the pads wear, the piston in the caliper travels outward. Since new pads are being installed, the piston needs to be compressed back into the bore. This will be done using a C-clamp.
- Open the bleeder valve on the caliper, and attach a brake-bleeding kit (figure L) that will be used to capture any fluid and debris that's evacuated from the caliper. Bleeding kits are available from auto stores, and cost less than $10.
- Place the C-clamp on the caliper, making sure that the clamp is not pressing on any lines, but is resting against flat surfaces on the caliper. Also, make sure that the clamp is centered on the piston so that it will go in straight (figure M).
- Open the bleeder valve, and begin tightening down the C-clamp to depress the piston.
Important: On older brake systems, the old brake fluid from the piston was sometimes simply forced back into the braking system, rather than bleeding it off. It's critical that this never be done with ABS systems. Any debris forced back into the system could cause serious problems, necessitating in a very costly repair. - With the piston fully depressed, tighten the bleeder valve (figure N) to prevent any air from getting into the system when the bleeder is removed.
- With the bleeder fully shut, remove the C-clamp.
- Reinstall the cap to prevent any debris from entering through the bleeder port (figure O).
- The next phase is the installation of the disc pads. The outboard and inboard pads both have distinct left and right sides, and it's critically they be oriented correctly when installed. Each pad has a wear sensor (figure P) -- a piece of spring metal that makes an audible squealing noise when the disc is worn beyond a certain point. (This sound alerts the driver when it's time to change brake pads, to avoid mechanical wear to the metal parts.)
- The clip for the wear sensor is mounted in a different location on the inboard and outboard pad (figure Q). The pads are installed so that the wear sensor is on the trailing edge of the outboard pad. Check the instructions that come with the brake-pad kit if you are unsure of the orientation or installation procedure.
- Once you have the correct orientation, snap the pads in place in the brake caliper (figure R).
- Lubricate the caliper mount pins (figure S), and reinstall the caliper as it was mounted before.
- Snug the pins down, then come back and torque them to the proper specs (figure T).
In the segment that follows, the rear brakes are serviced, and the brake system is checked for proper operation.
RESOURCES :
Automotive Brakes and Antilock Braking Systems
Model: 0314028382
Author: Kalton C. Lahue
(1995)
To order this title from Amazon.com, click here.
Delmar Learning
Brake Handbook
Model: 0895862328
Author: Fred Puhn
(1985)
Order this book from Amazon.com.
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