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Old 10-25-2015, 06:46 PM   #1
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Default Bleeding brakes - Pedal bottoming out

Lately I have noticed that while sitting with motor running I will push the brake pedal all the way to the "floor". There is resistance, but instead of a slight spongy feeling at the end there is a firm stop when I believe I am bottoming the master brake cylinder.

With car off I can pump pressure and pedal is firm and feels right, but then when starting motor I am back to pedal to the floor.

I do have decent brake performance when driving, but can`t help thinking that it should be better and that I should not be "bottoming" out like it does now. I have bled the brakes twice with a vacuum bleeder and put about 500ml of fluid through the lines and still no change.

Rear pads were recently changed and were adjusted tight and a quarter turn back. I will tighten a bit more tomorrow. Handbrake engages nicely.

I`ve seen several threads with similar issues, but none resolved. I have considered a brake master rebuild but found Hustlers thread where he changed like 70 of them and still had issues...

FSM has a description of how to adjust brake pedal height, but not sure if more pedal height will provide more travel in the brake master since there is what seems to be adequate free play now.

Any ideas?
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Old 10-25-2015, 10:43 PM   #2
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ABS car or not?

How is the stock proportioning valve shielded from the exhaust?

How about the left front brake line?

Pictures?
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Old 10-26-2015, 01:56 AM   #3
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Quote:
Originally Posted by lassi View Post
With car off I can pump pressure and pedal is firm and feels right, but then when starting motor I am back to pedal to the floor.
Air in the system.
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Old 10-26-2015, 03:54 AM   #4
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Originally Posted by sixshooter View Post
ABS car or not?

How is the stock proportioning valve shielded from the exhaust?

How about the left front brake line?

Pictures?
Everything is stock oem Mazdaspeed. ABS.

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Originally Posted by aidandj View Post
Air in the system.
I agree, but I`ve bled the *** out of this car now... Handbrake up and down, pumping the pedal, vacuum from each caliper etc... I`ll get a pressure bleeder and another liter of fluid and start over I guess...
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Old 10-26-2015, 09:26 AM   #5
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i had this problem once. i messed up reinstalling the prop valve bracket. i installed it behind the master. sandwiched in between the master and the booster. the pedal felt like crap and went to the floor. once i fixed it my world changed for the better.
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Old 10-26-2015, 04:15 PM   #6
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Isn't ABS bleeding procedure different?
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Old 10-26-2015, 05:07 PM   #7
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Isn't ABS bleeding procedure different?
Bleeding the ABS unit itself needs a data connection, but eveything else is as normal. Air in the ABS unit would only be noticed when it is active.

Could not find a local store with a pressure bleeder and a cap that would fit our reservoirs. Will order one. To be continued...
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Old 10-26-2015, 05:21 PM   #8
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You just need to ground a wire on the abs pump. or something like that. No data connection needed.
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Old 11-17-2015, 02:30 PM   #9
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FML... Still bottoming out. Nice stiff pedal until I start the engine, then goes to the floor. Kinda slowly, but I can still feel it bottoming out.

I bought a Motive pressure bleeder and bled all corners approx two fillings of the reservoir per corner, some tiny bubbles exited when I wiggled the brake hoses. Still no change in pedal feel.

Thinking I should try bleeding the ABS pump, I wired TBS and GND to put the ABS into self test. (hold brake+ignition on) while I had pressure on the reservoir and opened a bleeder. This should flush any air in the pump out. Ran 4 cycles per corner. Result - Worse pedal...
Directly after this I did some test driving with hard braking activating the ABS several times and then went straight in and started bleeding with the pressure bleeder. Did get a single big bubble on the right rear and some small on the left. Nothing on the fronts. Still not a firm pedal when the engine is running.

Could the problem be the master cylinder? I have no visible leaks, not loosing fluid or any other signs of failure I can think of. How would it feel if the internal seals in the MC are leaking? If its still just air somewhere I really cant think of how one is supposed to bleed this car properly.
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Old 11-18-2015, 08:48 PM   #10
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Disconnect the brake booster and run engine. Does it feel the same as before with engine running or engine off?

If it feels like engine running I'd guess it's the ABS.
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Old 11-19-2015, 12:57 AM   #11
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I think the whole engine off-engine on situation is a red herring. With the engine on, the booster is just providing much more force than you can with your leg alone, and is exposing any mushiness in the system. It's normal for the pedal to drop much lower when you have the booster augmenting your manliness.

Is this a new or existing condition? If new, and you haven't messed with anything in the brakes, I'd worry about a leak. A frequent mode of failure of master cylinders is that they leak internally and don't lose any fluid.

If you did mess with it, or it's been this way for as long as you've had the car, you might want to play with brake pedal height. For as long as I've owned my car I felt like I was bottoming out my pedal in hard braking, too. Through 2 sets of different brake pads and rotors, at least 3 thorough bleedings, 20k miles, and about 10-15 hours of mild-moderate track time, it never got better or worse. One day I adjusted the master cylinder shaft inwards, and my life got better. Then I insalled an MSM 15/16" master and booster (which you obviously already have), and now the pedal doesn't come anywhere near bottoming.

In conclusion, Libya is a land of contrast.*


*Actually, I think my conclusion is that once you're certain you have no leaks and no air in the system, first spend a few minutes playing with the pedal adjustments. Apart from having to bend yourself into the footwell, it's dead simple; just make sure you don't preload it so much that the brakes wind up binding when they heat up.

If that doesn't improve life, my next step would probably be to try a different master cylinder.

Edit: Here's the thread I started in my own spiritual journey to brake pedal happiness.

Last edited by TalkingPie; 11-19-2015 at 01:13 AM.
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Old 11-19-2015, 11:47 AM   #12
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Quote:
Originally Posted by stefanst View Post
Disconnect the brake booster and run engine. Does it feel the same as before with engine running or engine off?

If it feels like engine running I'd guess it's the ABS.
This would be the same as just pumping the brakes with the engine stopped.

Quote:
Originally Posted by TalkingPie View Post
I think the whole engine off-engine on situation is a red herring. With the engine on, the booster is just providing much more force than you can with your leg alone, and is exposing any mushiness in the system. It's normal for the pedal to drop much lower when you have the booster augmenting your manliness.

Is this a new or existing condition? If new, and you haven't messed with anything in the brakes, I'd worry about a leak. A frequent mode of failure of master cylinders is that they leak internally and don't lose any fluid.

If you did mess with it, or it's been this way for as long as you've had the car, you might want to play with brake pedal height. For as long as I've owned my car I felt like I was bottoming out my pedal in hard braking, too. Through 2 sets of different brake pads and rotors, at least 3 thorough bleedings, 20k miles, and about 10-15 hours of mild-moderate track time, it never got better or worse. One day I adjusted the master cylinder shaft inwards, and my life got better. Then I insalled an MSM 15/16" master and booster (which you obviously already have), and now the pedal doesn't come anywhere near bottoming.

In conclusion, Libya is a land of contrast.*


*Actually, I think my conclusion is that once you're certain you have no leaks and no air in the system, first spend a few minutes playing with the pedal adjustments. Apart from having to bend yourself into the footwell, it's dead simple; just make sure you don't preload it so much that the brakes wind up binding when they heat up.

If that doesn't improve life, my next step would probably be to try a different master cylinder.

Edit: Here's the thread I started in my own spiritual journey to brake pedal happiness.
I`ve already ordered a new master cylinder. I did look into adjusting the pedal, but have checked it and there is only a very slight free play. As I see it I have max travel on the cylinder and any preload would as you say risk binding and not give me any more positive travel\fluid pressure.

Leaning towards and internal leak in the main cylinder... Will update when I get a chance to replace it.
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Old 12-07-2015, 03:48 PM   #13
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Replaced the master and is just like before. I bench bled it, but I must have done something wrong somewhere. Still brakes decent, but pedal still bottoming out.

When pumping the pedal with car off I get air coming up into the reservoir? Why? This is after running 2 liters brake fluid through the system with the Motive pressure bleeder. Where is this air coming from?

Video;
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Old 12-07-2015, 05:07 PM   #14
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You definitely have air in the system. I don't know why.
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Old 12-07-2015, 06:04 PM   #15
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do you have speed bleeders?
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Old 12-07-2015, 06:50 PM   #16
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No speed bleeders either.

I'll try to bleed the master again tomorrow while on the car. I watched some video and can see that I might have sucked some air in by using the bleed kit I got with the new master. Lines too thin to let the bubbles travel freely up and I probably sucked them straight back while seeing no bubbles at the end. FML...

Still don't quite get where all the air coming back into the reservoir is coming from. Feels like I can keep it bubbling forever.

Thanks for your input guys. Will update tomorrow.
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Old 12-07-2015, 08:29 PM   #17
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Bleed it at the lines coming out of the master. Crack them open while an assistant holds the pedal. Up, down, crack line, up, down, crack line. When you have bleed it several times on each line, then pump up the pedal, then hold it, then open the fitting. Do this several times.

If the car has ABS, do the same at the input/output lines.


Then go to the brake hardline into the hoses, same deal. Then the calipers. Spray down everywhere with water afterwards to get the fluid off.




In my experience, vacuum bleeders are pointless for getting air out. They're great for flushing a sealed system. Actual, manual, bleeding works best. Based on the location of the bubbles, I'd say it's the closest channel to the firewall. If you want to save your expensive fluid, get a pedal with a gallon of cheap stuff, then flush it out with the vacuum bleeder.


EDIT: Bench bleeding will rarely get all the air out. I don't even bother anymore. Vacuum bleed the calipers from the master, then carefully bleed while letting the pedal slowly get closer to the floor, to avoid blowing it up.
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Old 12-08-2015, 10:05 AM   #18
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Bench bleeding seldom gets all the air out because installation usually reintroduces some air, but it does get the unit primed, which is the real point of it. I have used vacuum bleeders and pressure bleeders of various types over the years and still find the two person pedal pumping arrangement to be preferable. With a partner who follows instructions it yields perfect results with just a few minutes of activity. But you need to have your communication and timing right between the two.
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Old 12-08-2015, 03:21 PM   #19
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The video in my post above is after running 4 full reservoirs the old fashioned way...

Bled the master while on the car and installed the lines again. Ran 6 fills on the reservoir through to the left rear and not a single bubble came out. How is that even possible? I just introduced air into the system by removing the line but nothing coming out after 1 full liter of fluid flushed through!
This is by pressurizing the the reservoir as I had no friends to push the pedal for me today...

Obviously I`m not moving the fluid fast enough for the air to travel down either to the proportioning valve or from the ABS unit.
I did start to remove the pipes from the ABS unit, but the mess became too much for me to handle.

Have to get at it again tomorrow as I`m home alone with my 3yo son tonight.
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Old 12-08-2015, 03:40 PM   #20
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go on tinder, find any girl, make her push pedal
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