因為我的車的parking brake(緊急煞車)不是一般手拉或是腳踩, 而是電力控制,
2007 Audi A6 Quattro rear brake pad replacement.
This "how to" is mainly on how to retract the caliper piston on rear calipers equipped with a electric parking brake actuator. If you require more information on this job then you should probably get help from some of your more experienced friends.
First the safety stuff: make sure the key is out of the ignition and make sure that none of the doors get open to the car while you are working with any of the calipers. This vehicle will occasionally pressurize the brake system when the driver's door is open and can cause some serious injury if you got your fingers in the caliper.
There are many methods of doing this:
1. you can use a brake retract tool from Matco or Snapon that cost about $200.
2. you can use the Vag-com aftermarket tool which costs $350
3. you can use a C-clamp and some medium size channel locks. <--- Yes, its redneck, but it works fine.
4. you can manually apply 12v to the electric actuator to back it off. <--- For the more tech savvy.
I will be talking about method 3 and 4 as I feel that spending the money for 1 and 2 is not worth just for a brake job. If you have the tools for method 1 and 2 and you plan on using those, then this page will not work for you.
Firs off, the rear calipers work just like any other calipers that have a parking break feature. These only look complicated because they have a electric motor bolted to them and not a steel parking brake cable.
(Method 3) You can retract the piston by twisting to the right, just as you were tightening a screw and pushing in on it. I have proven this method with a C clamp and used channel locks to rotate the piston. There is enough room on the piston to grab it on the outer diameter, but make sure not to grab the rubber. (Put some WD-40 on the rubber around the piston to allow it to slip on the piston as you turn it). The Audi piston face has a 3 hole triangular pattern on it so a standard 4 or 2 prong retractor will not work. This method took about 5 min. to retract and I ended up with a sore hand. (Note, I removed the electric actuator so I would not press on it with the c-clamp, just remove the 2 small torx screws and pull it off, its just sitting on a rubber O-ring) Also, you can install the caliper upside down using the upper mounting bolt on the caliper bracket and this will face the caliper away from the rotor and make it much easier to work on then just having it dangle by the brake hose. Sorry, I forgot to take a picture of this setup. Total time for 1 wheel pad replacement was 20 min.
(Method 4) Operating the electric actuator manually. The actuator is not a servo, its just a 12v electric motor with a little gearbox that is used for high torque. The car's computer uses current detection to know if the brake is applied. This motor can be turned in either direction depending on the polarity of the voltage. Using this method, total time replacing the pads on 1 wheel was 5 min. (It took as long to make the test wires as it took for the pads)
1. First disconnect the cable going to the actuator.
2. Make wires to be installed on the actuator. See picture.
3. Install the wires on the actuator
4. Apply 12v to the actuator. In one direction it will apply the brakes. You want to go the other way to release the piston. You can use any 12v source that will supply more than 5A of current.
5. If you feel the electric motor straining up against a stop then remove the power. In the reverse direction the motor will run freely for about 5 to 10 sec.
6. After that you can push the piston back with ease, like with a small screw driver. If your using a big screw driver or a prybar with allot of force, then you did not retract the parking brake mechanism far enough. Stop forcing it. It should go super EZ.
7. You only need to undo the lower mounting bolt and then pivot the caliper upwards to remove and reinstall the pads. The wrench sizes are 15mm on the inner nut and 13mm on the outer. The 15mm will need to be a narrow wrench.
8. Once you have installed the new pads and reinstalled the caliper, drive the motor manually with voltage to where it just starts to clamp on the pads. You should still be able to spin the brake rotor by hand. If you went too tight then you can reverse
polarity and back it off some. (Note: this step may not even be necessary, I think the computer will take up the slack on its own once the parking brake is actuated. I'm not sure what the algorithm is for the circuit but if it takes too long for the circuit to achieve increased current the circuit may time out and flag the parking brake service light. But that should be able to be reset by working the parking brake a few times.)
9. Remove the wires
10. Connect the car's parking brake connector to the actuator. (Check both wheels)
11. Get in the car and step on the brake to take up any hydraulic/mechanical clearance in the caliper pistons and pads.
12. Insert key and turn the ignition on.
13. Apply the electric parking brake. This will self adjust the actuator. The car's computer will drive the actuator until a certain amount of current in the circuit is achieved. That's how it knows the brake is applied. You may need to apply and release a few times, maybe like 3. You may see a service parking brake alarm on you dash. This alarm will clear on its own after you have successfully cycled the parking brake a few times.
14. Test drive the car, especially if its your wife's car.
And you're done.
...as always, this information is free and I'm not responsible if you screw up your car.