Brake repair bleeding tips

I visited a friend to scrounge an old style plain (no level sensor) ATE master cylinder cap for my homebrew pressure bleeding project. We started trading stories, shortcuts and tips and I picked up a couple of clever tips; new to me at least. It wasn't all business though, a brewski or three were involved as well.

Avoid draining the master cylinder reservoir while bleeding
With a narrow neck bottle of your favourite brake fluid, turn the bottle upside down in the reservoir. Contrary to "common sense" the bottle will not empty. Rather the brake fluid will stay in the bottle until the reservoir level falls below the bottle's mouth. Then only enough will flow to submerge the mouth of the bottle again. So, you can bleed away with a one quart reserve automatically refilling the reservoir as required.
It would be good practive to wrap the master cylinder opening around the bottle of brake fluid with a clean, lint free rag or plastic wrap to minimize access of moist air to the brake fluid. Also surround the reservoir with catch rags to absorb any spills as you invert the bottle - unless you are very fast and very good.

You can verify the physics behind this effect with a bowl or sink and say a plastic bottle of drinking water. Fill the sink, fill the plastic water bottle. Quickly invert the bottle and stick the neck underwater in the sink; perhaps hold a finger over the bottle mouth until it is submerged. You will see a bubble of air in the bottom (now top) of the bottle. But the bottle will not empty itself until you lift the bottle clear of the water level in the sink. And flow will stop if you re-submerge the mouth.

Prevent loss of fluid while changing calipers, etc.
I've always cringed at the common habit of pinching rubber flex brake hoses to prevent draining the reservoir and "airing" the master cylinder. My friend had a solution. Before opening the brake circuit, depress the brake pedal and prop a stick against the seat to hold the pedal down. The master cylinder seals are now past the ports from the reservoir and there is no flow path from the reservoir through the master cylinder to the caliper. You will get a few initial drips from the open line, but not a steady dribble or stream.

BTW, I don't mean to insult anyone's intelligence, but this trick does NOT eliminate the need for bleeding after the repair. But you won't have to worry about bleeding air out of the master cylinder and ABS/DSC block. And your brake hoses won't be crushed, possibly damaged.

Avoid setting DTCs when pressure bleeding with EasyDIS
DIS has a service function to run the ABS pump and cycle the ABS block valves to flush any micro-bubbles off the fine ports and passages out into the brake lines to be expelled in further bleeding. However, it also wants the reservoir pressurized for this cycle. Pressurizing the reservoir, means the car's master cylinder cap must be removed for the pressure cap. And the ignition must be turned on for EasyDIS to communicate with the DSC/ABS module.
Don't do as I did and simply lay the car's cap aside. The level sensing float will fall to the bottom and set a couple of DTCs. Instead, place the cap upside down so the float falls toward the cap, i.e. the high/full position. No DTCs will be set.

great info

When I did my bleeding i ended up with EasyDIS bleeding as i left my master cylinder reservoir open
as result got air into brake system and re-bleed my brakes 3 times ( last with EasyDIS )
I learned the hard way

http://forums.bimmerforums.com/forum....php?t=1859183

hhmmm I did a 10-15psi power flush using Motive Bleeder tool. I'll have to see about the module bleed procede.

rdl, a great suggestion! Ambient air pressure on the surface of the brake fluid in the reservoir is greater than the weight of the brake fluid in the bottle. This is what keeps the brake fluid in the bottle from exiting. Once the surface drops below the tip of the bottle neck, the brake fluid can drain until air pressure against the surface area stops the flow again. Super simple and a GREAT IDEA! Who said 9th grade physics was a waste of time!!!

Originally Posted by FLE39

hhmmm I did a 10-15psi power flush using Motive Bleeder tool. I'll have to see about the module bleed procede.

After having done a pressure bleed with using the DIS procedure, which includes the ABS module cycling, I wouldn't pay to have the DIS process unless I had a soft pedal that I couldn't solve and therefore suspected air in the ABS valve block. Or if I had replaced a master cylinder, ABS block or the precharge pump. Using the DIS procedure I found no improvement in the pedal.

However since I have EasyDIS on my laptop I will probably do my next flush in 2 years with DIS, but only because it's free. It can't hurt, might just help.

The bigger benefit was the pressure bleed with my home made version of the Motive pushing new fluid automatically into the reservoir as old fluid was bled at the calipers. It was nice to bleed without worry of a dry reservoir.

Better yet, I was able to bleed single handed with pressure on the reservoir. I attached an upside down U of tubing from the bleeder screw to a catch bottle. The tube filled with brake fluid on the bleeder leg of the U and that stopped any back draw of air into the caliper. I was then able to pump the pedal with bleeder open ~1/8 turn and pump fluid through the system to flush. None of the old open bleeder - down pedal - close bleeder - up pedal business.

Originally Posted by Fudman

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Super simple and a GREAT IDEA!

Aren't most good ideas simple ... once someone thinks of it!
I wish I could claim credit for it, but I'm just passing it on.

I posted RDL's hints to the canonical brake bleeding threads so that the information is best leveraged to future owners.

- How to bleed E39 brakes (1) (2) (3) (4) (5)