[dborg]

Hi All,

I’m planning to do some brake work next weekend on my E93 and had some questions about the process. I've looked through plenty of old posts trying to get the answers but have had no luck. I will be replacing the rotors and pads and while everything is off I was planning on painting the calipers as the rears are starting to rust. I am going to use one of those brush-on paints for the time being, in the future I may get them powder coated when I have more time to make the arrangements and depending on how the brush-on stuff holds up. I understand that using the brush-on paint can be done without removing the calipers, however, I really wanted to take them completely off so I can clean and paint them much easier.

I've read the Bentley manual and it says that if you introduce air bubbles into the lines, just bleed the brakes and you’re good (paraphrasing). Then it goes on to describe that if air gets into the master cylinder you need to hook up to the system and use software to flush everything out. Sooo…. What’s the best process for disconnecting the caliper and preventing air from entering the system?

My plan was to disconnect and plug the line with something, some air may get in but then bleeding the lines should remove this air pocket, correct? Would the air travel back to the master cylinder at all?
From what I've read throughout the forums, the only way air will get to the master is if the reservoir goes dry, is this correct?

[LMB335IS]

You are correct in that no air will get into the master cylinder as long as it doesn't go dry. I just did a total brake job this past week. (Powder coated front calipers, Z4 35is aluminum rotors, Hawk 5.0 pads all the way around, stainless steel brake lines, and removed and painted rear calipers) I went to a parts store and got some small rubber vacuum caps and plugged the brake lines as I worked around the car to keep fluid loss to a minimum. Never got remotely close to running it dry. Tried my new Schwaben pressure bleeder which worked beautifully and found a very small amount of air in the system. I would expect the same for you. Loosen the fill cap on master cylinder before you start to release any pressure and you'll be fine.

[dborg]

Good stuff. Would you happen to remember what size vacuum caps you picked up?

What was your process when you reconnected everything? Did you keep the bleeder valve open and reconnect the brake fluid line so that the air got pushed out right away?

[LMB335IS]

I just bought a bag of various sized ones. I used the smaller sized ones, 1/8-1/4 inch should work. Keep the bleeder closed until you actually bleed the caliper. You wont build any pressure and force the air out with it left open. Are you using a pressurized bleeder or going old skool and having someone pump the pedal?

[dborg]

I'll be using a pressurized bleeder, although I will have a buddy giving me a hand.

[TheBigYahi]

Press the brake pedal down a bit (halfway?) with a bar wedged into the front of the driver's seat. This closes a check valve (isolates the master cylinder from the reservoir) and creates a closed system like having your thumb over the end of a straw. I was working on stainless brake lines this weekend (what a disaster, story for another time) and I only lost a few drops per corner. Same deal when I replaced my rear calipers a couple months ago.

[mweisdorfer]

Get a mitivac brake bleeder.

Hook it up to your air compressor and then hook up the vac line to the bleed screw.

I think You will need an 8mm wrench to open the bleed screw.

Don't open the bleed screw until the vac is on and sucking, then open the bleed screw about 1/2 to 3/4 of a turn.

Prior to hooking up to the bleed screw....

At the other end, you will position a 40oz Gravity Feed, full bottle of Dot 4 brake fluid over the master cylinder, which comes with the kit.

You suck out the old fluid until you have clear fluid, which will probably end up being 5 to 10oz. Per caliper. You start with the passenger rear left, then go drivers rear right and then go to the passenger front and lastly drivers front.

It's a one man job, but it's much easier with two people.

Once your compressor gets below 50# psi, shut the bleed screw, then turn off the mitivac and let it recharge to around 150# psi.

If you do this correctly, you should not have to bleed the brakes, for you basically just did that and you get new fluid to boot, which your supposed to change it out anyhow every 2 years. Biggest key is to shut the bleed screw before you shut off the mitivac and allow the air compressor to recharge to 150# psi. Otherwise, you WILL introduce air into the lines.

Preparing the calipers for paint?

Probably the best thing to do is use a wire wheel in your drill. Dewalt makes a nice one. Put the caliper in a vice and brush away. While your add it, you may as well wire brush and paint the caliper holder as well.

I bought new clips that go on the front and painted them. They tend to rust if you live in a cold weather state that uses salt on the roads.

Brake Caliper Paint?

G2 is the best, but you have to let it dry a good 2 days before you put them back on the car, and your window of time is about 12 hours to paint and then add a second coat. Yes, you should add a second coat. After that, the paint hardens up and is no good. One small can does all 4 calipers and the caliper holders no problem.

http://www.g2usa.com

You can buy it on amazon or eBay.