gcheddar

I wanted to clarify something here before I screw something up:

I'm replacing my rear brake pads on my 2000 A6 4.2 ART - just the pads.

What is the sequence for bleeding the brakes/calipers? And how much fluid should come out into the catch bottle?

Initially I was thinking that I would attach the bottle to the bleeder nipple, open the nipple, wind back the caliper, then close the nipple.

But when looking at the instructions that came with the caliper reset tool that I got from MetalNerd (http://www.metalnerd.com/cat08.htm), it says to avoid that and only bleed the caliper after resetting it.

Does that make any sense? I thought rewinding the caliper without bleeding first could overpressurize something of force old fluid back into the brake fluid reservoir in the engine compartment leading to a leak.

Also, is it necessary to remove any brake fluid from the main reservoir? Or is it good enough to just eyeball it and keep the fluid level between the min and the max?

Thanks for any info.

Cheers,

George

im_cecil

Nothing you're going to be doing will open up or introduce air into the lines.

Remove old pads. Use the tool (I had to go to your link to figure out what you meant by 'wind back the caliper') to push the piston back into the caliper, insert new pads, done.

The only reason you need to push the piston in is because the new pads are obviously thicker than the ones you're replacing. You might take the cap off the brake fluid reservoir, but that's it.

If you want to bleed them anyway, do so after the new pads are in. They are 2 completely separate sets of tasks.

Generally, the bleeding order is to start with the wheel that's the furthest away from the reservoir/master cylinder. Then work your way to the closest.

MP4.2+6.0

That's the Audi spec. Since I started following it many Audi's ago, I haven't lost any hydraulic brake parts.

Actually, if you have topped up the reservoir all the way, you may need to siphon a bit off or it will overflow when you wind in the caliper piston.

If you bleed it, do NOT under any circumstances let air get into it by pumping too much. If you do, it is really hard to get it out of the ABS and you risk having bad things happen. If reservoir is full, I find 15 pumps+ is no problem before refilling.

I've found bleeding Audi's usually firms up the pedal some too, a nice result.

im_cecil

it's still not part of a pad change.

Trying to keep this simple... doesn't sound like the OP has done this before. Opening up the bleed nipple and letting it sit while swapping pads is not a good idea.

BernieBenz

Hence with any pad change it is best to flush the entire brake hydraulic system, all 4 calipers. Retracting caliper pistons will force fluid back into the MC reservoir, don't allow the MC to overflow. One should replace pads first, before flushing. Prior to flushing remove as much of the old fluid from the reservoir as possible with a turkey baster before adding the new flushing fluid. Flush until clean fluid is being flushed from each caliper.

BernieBenz

works as well as does pumping, pressure or vacuum.

Just Me

2 year old brake fluid has accumulated a lot of water.

You can generally just remove the reservoir cap and screw the caliper in - just check that you dont overflow.

Then flush it all out. I'd go about 250ml first wheel and 150ml+ on subsequent ones.

If you dont track the car (therefore wanting higher dry temp racing fluid like ATE) castrol LMA doesn't pick up as much water as most.

Grant

gcheddar

Cool. Thanks guys for all of the advice.

In my case, its been less than two years since the brake system was flushed. So it sounds like all I have to do is open up the reservoir while resetting the caliper and ensure that the level remains between the min and max. No caliper bleeding necessary. Sound right?

Now if it were over two years, we'd be looking at a full flush. In which case, the flush would really be a separate procedure from the brake pad change.

Now, in a year or so, I will need to do a full flush. And it sounds like the steps there are: use pump/turkey baster to remove fluid from reservoir; add new DOT 4 fluid; bleed each caliper according to bentley repair guide order (RF, LF, RR, LR) using a pump on the reservoir to pressure the new fluid through the lines and force out the old fluid.

The only question I have hear is that the repair guide talks about using a scan tool to activate the ABS/ASR hydraulic pump for 10 seconds. What's that about?

Thanks again guys!

Press

from farthest away to closest

gcheddar

Actually, according to page 47-4 of Bentley's Audi A6 C5 platform service manual it says:

"""
The design of the ABS hydraulic unit requires that brakes be bleed [sic] in the following (non-traditional) order:

o Right front
o Left front
o Right rear
o Left rear
"""