|
ABS Disc Brakes - Diagnosis and Disassembly
- Brake Service - Diagnosis an Disassembly
- Important:
These are the steps in this automotive procedure 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 Note that come with your kit or replacement parts.
- Note:
As a standard safety precaution, always disconnect the vehicle's negative battery cable before you begin work on any electrical or mechanical components.
- Checking the Faulty Sensor
- With the problem code indicating a faulty ABS speed sensor on the left-front wheel, the next step is to check that sensor directly using an ohm-meter set to the 20k scale. If the probes of the meter are brought into contact, a closed circuit is indicated by a zero reading.
- The speed sensor is connected to a disconnect plug underneath the hood. With the probes connected to the terminals on the plug, the circuit is checked for continuity.
- A reading of 1 on the meter reveals an open circuit, which indicates a bad sensor -- confirming what was indicated earlier by the datalink diagnosis.
- The next step is to remove the faulty speed sensor, which is held in place by a single bolt. With the bolt unfastened, the sensor can easily be taken out.
- Note: This particular sensor includes the wiring harness as an integral part, so it is removed also. On some vehicles, the harness can remain in place when a faulty sensor is removed. Check your service manual to be sure.
- Brakes Disassembly and Inspection
- It's likely that the vibration in the steering wheel is caused by a warped front rotor. In order to check, the front brake assembly must be taken apart.
- First, remove the caliper. It's held in place by pins that fit into rubber bushings to hold the caliper on tight. The pins will be checked for wear later.
- In order to prevent the removed caliper from simply dangling by the hose to which it's connected, a temporary support hanger can be fashioned out of coat-hanger wire. In that way, the caliper can safely hang suspended from the coil spring while the work proceeds.
- Next remove the caliper-mounting bracket by disconnecting the two bolts that hold it in position.
- With the caliper and bracket removed, the rotor itself can be removed and inspected. This one appeared to be in fairly good shape, but it's still best to have the rotors turned as part of this service. Turning the rotor means refinishing the surface by machining off 1/10,000th of an inch of metal to eliminate any irregularities.
- Next, inspect the rear disc pads for wear. A cut-out in the caliper allows visual inspection of the inboard pads for wear. In our case, there was significant wear to the pads. Therefore, the pads will be replaced and the rear rotors will be resurfaced as well.
- The rear brakes are disassembled in much the same manner as the front. A major difference is that the caliper of the rear brakes is connected to the emergency brake. The lever for the emergency brake is held in place by one lock-nut. Remove the nut and position the lever out of the way.
- As on the front brakes, now you can loosen and remove the two pins holding the caliper in place.
- With the pins removed, the caliper can be disconnected and moved over to the side. In this case, the caliper can safely hang by the emergency-brake cable as work proceeds.
- Tip: When servicing the rear brakes, it's a good time to check your emergency brake for signs of wear. Also check all of your brake-fluid lines.
- With the caliper out of the way, loosen and remove the caliper-mounting bracket -- just as it was done on the front brakes.
- Now, the rear rotor can be removed and inspected. Note the difference between the front and rear disc brakes. The front rotors consist of two plates with ventilation ribs in between. The rear rotors consist of just a single plate. In front-wheel drive vehicles, about 70 percent of the braking force is in the front of the vehicle. For this reason, the front brakes are bulkier than those on the rear.
With this phase of the job complete, the rotors are sent to the machine shop for resurfacing. A new speed sensor is purchased as well. In the segment that follows, the brake servicing continues on the front brakes.
|
