Change Your Brake Fluid

[93 525 Paul]

You forgot to compress the caliper pistons as thats where the majority of the dirty brake fluid is

My expectation is that the old fluid is displaced by the new fluid. It doesn't seem that he new fluid would run clear until the caliper fluid is out. I used a clear tube on the bleeders and didn't close the bleeder until it ran clear. The volume of dark fluid is far greater than the volume of the lines, so it would suggest that the caliper fluid was indeed flushed.

[bad_manners_god]

My expectation is that the old fluid is displaced by the new fluid. It doesn't seem that he new fluid would run clear until the caliper fluid is out. I used a clear tube on the bleeders and didn't close the bleeder until it ran clear. The volume of dark fluid is far greater than the volume of the lines, so it would suggest that the caliper fluid was indeed flushed.

Doesn't work like that, the fluid that is inside the calipers is sitting at a lower level than the bleeder, since air is lighter than fluid it will rise to the top and bubble up which is why the bleeder is at the highest point, as soon as you would have compressed the piston, the rest of the black fluid would come out.

[Ross]

A lot of the crappy fluid will remain in the bores of the calipers. If you crack open a bleeder now after it had a chance to mingle with the new you'll see. The new fluid doesn't circulate through the caliper but takes the easiest path to the bleeder.
Retracting the pistons, bleeding, operate the brakes to re-extend the pistons and repeat will get pretty much all of it.
I usually don't go to the trouble unless the fluid was really crappy looking, like yours was.

[xspeedy]

A lot of the crappy fluid will remain in the bores of the calipers. If you crack open a bleeder now after it had a chance to mingle with the new you'll see. The new fluid doesn't circulate through the caliper but takes the easiest path to the bleeder.
Retracting the pistons, bleeding, operate the brakes to re-extend the pistons and repeat will get pretty much all of it.
I usually don't go to the trouble unless the fluid was really crappy looking, like yours was.

Is there an easy way to perform the retraction of the piston short of removing the caliper and pads (as done when swapping pads)? If not, I also heard it isn't a good idea to apply the brakes with the caliper out for fear of ejecting the piston completely.

I guess I'm asking for the best practice for this job. I flushed my brakes but never cycled the pistons. I'd like to go back and do this.

[Ross]

On the fronts which are floating simply prying the rotor against the caliper. Insert a large screwdriver into the vent holes of the rotor through th eopening in the caliper and pry it to push the pistons back. If you do it with the bleeder openthe fluid will be expelled rather than pushed into the lines.
The rear will require you to push each side in as the caliper is fixed. Again a screwdriver against the rotor being careful not to gouge anything.
There are expanders sold for this purpose also.

[xspeedy]

Thanks Ross. Rears are fixed? I recall mine as floating - 94 525i. I'll give the screwdriver trick a shot.

[93 525 Paul]

A lot of the crappy fluid will remain in the bores of the calipers. If you crack open a bleeder now after it had a chance to mingle with the new you'll see. The new fluid doesn't circulate through the caliper but takes the easiest path to the bleeder.

Hmmm. I'll give that a shot. Seems counterintuitive that clean fluid can be in close proximity with dirty and not intermingle.

[xspeedy]

Hmmm. I'll give that a shot. Seems counterintuitive that clean fluid can be in close proximity with dirty and not intermingle.

Well, if you are like me and don't open your bleed screw when you push the piston back in, you are pushing the fluid back into the line. Then when you are done with the pads, if you do a line flush, you are probably getting that fluid.

Not as good as a few cycles of fresh fluid into there to clean it all out, but better than nothing. Based on this thread, I'm going to change up my brake job scheme.