slabsquathrust

So my brake pad warning light came on a few months ago. I don't drive too often and kept a close eye on the pads themselves. However, it is now time for a replacement. Various shops have priced it in for about $400 to replace the pads on the entire vehicle and to turn the rotors. However on closer inspection the rotors have a fairly large rim and may be to worn for resurfacing and need a replacement. I can imagine this will boost the cost significantly. At those costs I figure I can do this job myself and save some money.

I found this link that details the braking system for the c5 a6.
http://www.vaglinks.com/Docs/Audi/C5...akeSystems.pdf

I have also found a number of videos providing an overview of the project. The primary difference between all procedures was the resetting of the pistons. Some videos showed the opening of a bleed valve while others said they pulled some brake fluid off the top of the master cylinder reservoir. Which of these is the better option?

A6Gary

Probably easier to withdraw some fluid out of the reservoir. After you replace all of the pads, re–check the fluid level and add/subtract as necessary to reach the MAX line.

5v/cyl

Go for new rotors.

Audi recommends changing the brake fluid every 2 years. Brake fluid absorbs moisture over time, decreasing boiling point, and flushing also gets any contaminants out. I just do it when I do a brake job.

Using a turkey baster I suck the old fluid from the MC reservoir and pour in fresh before I start. Then as I do the brakes at each corner I bleed the line until I get fresh fluid before doing anything else. Now you can just push the piston in and let the clean new fluid go back to the MC. One final quick bleed after new brakes are installed and on to the next corner. I use a power bleeder, but a helper to push the pedal works as well.

Keep an eye on the fluid level in the res. so you don't run out and at the end of the job top it up to the correct level.

SloopJohnB@mac.com

Here's the deal....you don't need special tools to do the front, but you DO need a tool (various costs) to retract the rear brake piston in its caliper cylinder.

Basically the piston needs to be rotated while pushing it in. There is a special tool that does this mechanically as well as the pneumatic tool I have (rotate the piston with a handle and use air to push it in). Google for a tool.

Most people evacuate the master cylinder before doing anything, refill with new fluid from an unopened container. Do not use DOT5 silicone fluid...not so good for ABS. Use DOT4....you'll need about two liters to do it right.

I recommend a pressure bleeder or a mity-vac type of suction bleeder. The mity-vac will only let you pull about 8 oz before you have to fool around with dumping the little container. The pressure bleeder from bavauto.com rocks! Highly recommended, it has a quick disconnect for the cap at the master cylinder that really makes it easy to put on the car.

http://www.bavauto.com/fland.asp?part=PB03K

When you get around to pushing pistons back into calipers, I recommend loosening the bleed screw...you'll have to do it anyway to bleed the calipers and if you do it now when you push the pistons back in you will eject old fluid rather than pushing it back up the pipe and potentially into the ABS system. After you put in the new pads, bleed the system.

AS a general rule, you can just slap in new pads and they'll bed to the old rotors soon enough...some people knock off the outer edge (inside and outside of rotor) ridge with an angle grinder...you'll get about 4mm more wear (2mm/side) on the pads before metal to metal. If you don't grind off the ridge the ridge will hit the pad backing plate before the pad is worn out. If your rotors aren't scored, etc., just put in new pads. That being said, Audi's wear limit on rotors is ridiculously small...only 1mm per side!!! So for the record your rotors are automatically worn beyond Audi wear limit. Personally, I just put new pads on at least two-three sets of pads per rotor set.

Last but not least, check the guide pin lubrication on the calipers...unless you have aftermarket (RS8, Brembo, etc.) calipers with inside and outside pistons, the caliper floats on guide pins. The guide pins need to be cleaned and lubricated, often with each pad job, so that the pads don't wear unevenly. Dragging guide pins will often cause the outer pad not to wear as much as the inner pad. Braking force is also reduced and rotor temperature is uneven with the inner side heating up much more than the outer side and much more than would otherwise occur with both pads and both sides of the rotor getting equal pressure.

Just Me

1. i suspect you can keep the rotors. If you do, do not turn them, just leave them alone. Turning removes material and creates out-of-round,a nd replacemenbt is rarely necessary.

2. you'll want to change the fluid while you are in there, right? Right? So whether or nto you open the bleeder valve is not very important.

3. To avoid unpleasant surprises, i strongly urge you to use OEM type pads - not necessarily from the dealer, but a similar compound. You know there will be no incompatibilities, and you might find the engineers at Audi are not as dumb as the aftermarket thinks.

4. Really big channel locks are your friend.

5. As Sloop says, you need a special tool for the rears. Harbor freight sells a nice kit.

G

Just Me

All good advice except for the new rotors. A reason WHY they are needed would be helpful.

Will they be nice? Sure. But they will also be costly and greatly complicate the job. Measure them. If the total wear is less than 3mm - you dont need them (front). You never, ever, ever wear out the rears. Mine have 80k on them and measured 15% wear compared to the factory limit, which is stupidly tight.

G

SloopJohnB@mac.com

I have been unable in over 40 years to get a straight answer from ANY brake engineer as to how they set rotor wear limits.

Among the variables that are considered, if not tested with ANOVA matrices, are rotor mass (ability of the rotor to suck up heat energy and therefore heat up less during transient conditions, not steady state), caliper piston extension at brake pad maximum wear (piston must not come out too far, get cocked, etc.), ability of the rotor to maintain structural integrity, i.e, how thin till it cracks or breaks, etc.

I just do not see the one mm wear limit audi puts on their rotors in terms of any of the above.

Just Me

concur.

If a) was the answer, C5s wouldbe unsafe with standard brakes
if b) was the answer, thin brake pads would be "right out"
if c) was the answer, my present rotors would be in two pieces, and/or i would not be typing.

QED, its set by lawyers.

G