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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 09-22-2013, 10:17 PM   #1
patriot_man
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No resistance in brake pedal - Air in brake master cylinder?

So I've bled the brake lines 3 times but the brakes still just go to the floor with any force. There is no resistance, no pressure. I've read around and it seems to be air in the brake master cylinder.

I didn't have the proper fittings for the bleeding so I just submerged the whole master cylinder + brake reservoir in a small container filled with brake fluid and pumped until air stopped coming out. Was this the right thing to do? Was I supposed to install it back into the car with the reservoir full? I didn't think so since the whole thing was dripping out brake fluid out of the master cylinder holes (cap tightened).

So now I installed the cylinder + reservoir and found out that the brakes were still the same. I bled the brakes again with the motive and used INPA to cycle the ABS on both sides. No bubbles coming out.


Current situation: The master cylinder + reservoir are in the car. I'm loosening the lines that lead to brakes and I'm having a helper press the brakes to hopefully release some air out of the cylinder. I re-tighten and tell my helper to let go of the brakes. So far I've had fluid come out and what I think is air. Will this work or am I just kicking rocks?

Edit: I've done it about 6 times on each line. I'm going to do it 20 more times on each line and see what happens. If nothing happens I'm going to call it quits for now...

Last edited by patriot_man; 09-22-2013 at 10:21 PM.
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Old 09-22-2013, 10:49 PM   #2
lszlszx
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The helper is supposed to pump 3 times, then hold while you open the line.

I think your submerge method didn't work, the piston needs to move in order to get filled up with brake fluid.
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Old 09-22-2013, 10:59 PM   #3
patriot_man
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Quote:
Originally Posted by lszlszx View Post
The helper is supposed to pump 3 times, then hold while you open the line.

I think your submerge method didn't work, the piston needs to move in order to get filled up with brake fluid.
Ohhhh. I thought releasing before closing off the line would suck air back in?

Yea I pushed the piston back and forth until the air stopped coming out.
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Old 09-22-2013, 11:15 PM   #4
patriot_man
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I'd also like to add that on ignition without the car on the pedal is super, super firm. I'm not sure if that means anything but thought it'd be good to add.


So when I do a bench bleed and transfer the master cylinder to the car (cap closed) is the fluid not supposed to come out? I don't see how else you would install it with the fluid pouring out.

Last edited by patriot_man; 09-23-2013 at 12:44 AM.
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Old 09-23-2013, 05:15 AM   #5
paraklas
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Quote:
Originally Posted by patriot_man View Post
So I've bled the brake lines 3 times but the brakes still just go to the floor with any force. There is no resistance, no pressure. I've read around and it seems to be air in the brake master cylinder.

I didn't have the proper fittings for the bleeding so I just submerged the whole master cylinder + brake reservoir in a small container filled with brake fluid and pumped until air stopped coming out. Was this the right thing to do? Was I supposed to install it back into the car with the reservoir full? I didn't think so since the whole thing was dripping out brake fluid out of the master cylinder holes (cap tightened).

So now I installed the cylinder + reservoir and found out that the brakes were still the same. I bled the brakes again with the motive and used INPA to cycle the ABS on both sides. No bubbles coming out.


Current situation: The master cylinder + reservoir are in the car. I'm loosening the lines that lead to brakes and I'm having a helper press the brakes to hopefully release some air out of the cylinder. I re-tighten and tell my helper to let go of the brakes. So far I've had fluid come out and what I think is air. Will this work or am I just kicking rocks?

Edit: I've done it about 6 times on each line. I'm going to do it 20 more times on each line and see what happens. If nothing happens I'm going to call it quits for now...
When I changed my brake booster, I emptied both fluid reservoir and brake cylinder. Here's my bleeding process which resulted in super firm brake pedal:

1. Re-install everything, empty
2. Pour DOT4 brake fluid on the brake reservoir until full
3. Check for leaks, you don't want brake fluid on the paint
4. Remove farthest wheel from the brake reservoir
5. Person 1, pump brake pedal until hard and keep pressing it
6. Person 2 Attach a drain tube to avoid a mess on the caliper bleed screw
7. Person 2 While pedal is still pressed, loosen bleed screw, bubles/fluid will squirt and pedal will start traveling now
8. Person 2 Right before the pedal reaches the end, tighten bleed screw and THEN Person 1 release pedal.
9. Repeat steps 4-8 at least 20 times per wheel.
10. Every 3-4 pumps check brake fluid level. Never let it empty

I found that after I did the repair, all air had been trapped to the front left wheel caliper/line. Initially it was squirting brake fluid but after 4-5 repeats, it started blowing air as well.
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Last edited by paraklas; 09-23-2013 at 05:16 AM.
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Old 09-23-2013, 09:09 AM   #6
patriot_man
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Thanks. I'm just hoping that it isn't something wrong with the master cylinder.

So should I do the pumping with the brake resivoir cap on or off? Thanks.
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Old 09-23-2013, 09:20 AM   #7
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Also I'm still curious if the resivoir with the cap closed is supposed to prevent fluid from coming coming out?

Sort of like having a straw filled with water and holding your thumb over one end. I'm trying to determine if there is a leak or something on the resivoir/MC assembly.
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Old 09-23-2013, 01:11 PM   #8
paraklas
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pumping should be with the cap off. The cap closes firmly but I not enough to build negative pressure, it should allow some "breathing" as brake pads wear out and the fluid level gradually becomes lower.

A faulty brake cylinder can leak inside the brake booster (bad)
The 2 rubber seals between the brake cylinder and the reservoir may leak - I had to push the reservoir quite hard to snap it in place
Leaky clutch cylinder will also drain some of the fluid
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Old 09-23-2013, 03:27 PM   #9
patriot_man
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When you "some breathing" is it just drips because mine just pours out of the holes.

Last edited by patriot_man; 09-23-2013 at 03:29 PM.
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Old 09-23-2013, 03:28 PM   #10
patriot_man
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Also I'm assuming the clutch cylinder is only in manuals right? Thanks
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Old 09-24-2013, 12:20 AM   #11
paraklas
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Quote:
Originally Posted by patriot_man View Post
When you "some breathing" is it just drips because mine just pours out of the holes.
What holes? brake fluid should only come out from the bleeder screw on the brake caliper.

Can you explain a bit where the fluid comes from?
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Old 09-24-2013, 01:28 AM   #12
patriot_man
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Ok so I did just as you said paraklas and the brakes finally work . That being said they are not super firm.

What I meant was after I did the bleeding of the master cylinder I would take it out of the brake fluid and the brake fluid would just pour out of these two holes. I thought there would be some negative pressure with the cap on to prevent the fluid from coming out in order to install it back onto the car. I found it odd and thought perhaps there is a leak somewhere between the reservoir and Master Cylinder.

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Old 09-24-2013, 02:17 AM   #13
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oh, I see what you mean now.. It is perfectly fine and correct for brake fluid to pour from the brake cylinder hoses even with the reservoir cap closed.

I think if you repeat the bleeding process eventually the brakes will become super firm, perhaps repeat the ABS open/close process as well. sometimes there's just a bubble in the middle of the brake line which f*** everything
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