Dispelling myths and BS: How you REALLY are supposed to bleed brakes

[flatlander937]

I'm sure you have heard when bleeding brakes... you "start at the wheel furthest away and work closer to the master cylinder." This does not apply to the Mazda 3... it has a diagonally split brake hydraulic system... not a front/rear split like cars of yester-year and most trucks/SUVs.

The left rear and right front circuits are on the same port in the MC... and the right rear and left front circuits share the same port.

The benefit to this is that you will only lose 50% of your braking ability should one circuit start leaking. In a FWD car with a front/rear split, if you lost the front then you would lose about 70+% of your braking ability... not to mention locking up rear brakes would potentially spin you in a hurry, making the situation even worse.


The only reason that the old "start with the wheel furthest from the MC" BS was started was because back in the day cars only had ONE type of brake hydraulic circuit... the fronts were on their own circuit, and the rears were on their own circuit. So of course the rears are the furthest away... so going by that logic you bleed the rear circuit before the fronts... which is exactly how you're supposed to do it on a front/rear split system.


When you bleed the brakes in the "old" and wrong method(on a diagonally split system)... you bleed the right rear just fine... but when you go to the left rear next, you are starting a new circuit entirely... so every time you pump the pedal to bleed the left rear, you are sloshing brake fluid in the RR-LF circuit back and forth, adding a zillion bubbles of air because the new fluid you JUST put in there is getting aerated because it's not going out in one direction.


Also I constantly see people struggle with bleeding brakes and nearly EVERYBODY completely screws it up and ends up with only an "acceptable" pedal when done... but when done properly it is so much better.


The proper way to bleed brakes is to do this(for each wheel... in the correct order... discussed below) if you have a helper available:

1) Have helper stand on brake pedal

2) Crack bleeder screw. (Your helper will/should feel the pedal go to the floor... make sure they do not let up until step 4!) Use a clear hose to watch bubbles leave the system and pay attention to the color of the fluid.

3) Close bleeder screw when flow stops

4) Have helper SLOWLY let pedal up

HERE IS WHERE EVERYBODY COMPLETELY SCREWS IT UP!!! IMPORTANT: DO NOT under ANY circumstances let your helper "pump up the brake pedal." All they are doing is aerating the fluid and introducing more air into the system that you just started bleeding. It is a LOT easier to get out one large air bubble than it is to get 10,000 little micro-bubbles out of the system. The smaller the air bubbles, the more likely they are to stick to the walls of the inside of the tubing... letting fluid go around the air defeating the purpose of bleeding.

5) Have helper step on pedal again... note that it will feel soft and feel like crap, etc etc. Again... do NOT pump the pedal until the VERY VERY end! Fluid WILL come out when the bleeder is cracked! Just the pedal will not feel very responsive until the END.

6) Crack bleeder screw again and watch fluid leave the hose again. You can even listen for air bubbles and know if you're in a not too loud environment

7) Close bleeder when flow stops

8) Have helper slowly let pedal up again

Then you repeat this until the wheel you're bleeding is good, then go to the next wheel. BE SURE TO CHECK THE MASTER CYLINDER RESERVOIR CONSTANTLY TO ENSURE YOU DO NOT RUN IT DRY! GETTING AIR OUT OF THE SYSTEM WHEN THE M/C INGESTS AIR IS CONSIDERABLY MORE TIME CONSUMING. I generally top off the M/C at the start of each wheel, and check/top off about every 4-5 "pumps" with the bleeder open. Start out checking a bit more often to get a grasp on how quickly the fluid is displaced to minimize the risk of putting air into your system!!!

AGAIN... DO NOT "PUMP PUMP PUMP PUMP PUMP" to make the pedal "feel" hard until all 4 wheels are bled and you are done. It doesn't matter what the pedal feels like while bleeding, the idea is to only make the fluid move in ONE direction... that is towards the calipers and out of the bleeder. By pumping it, you slosh it back and forth and intermix good fluid with bad, and more importantly(and stupidly) fluid with air.

I guarantee you will not get a better feeling pedal by doing it any other way manually.

I bled the brakes on my 09 Mazda3i today and verified it is indeed diagonally-split hydraulically.

(Sorry for the super crappy quality pic... my phone's camera is terrible)

I figured it out by having my friend hold the brake pedal, I cracked the right rear bleeder, and with him still standing on the pedal to hold it at the floor, I walked around to see which rotors I could spin by hand. Surprise-surprise... with the right rear bleeder cracked, the right front and the left rear rotors were clamped solid... the right rear and left front were free to spin since there is no hydraulic pressure acting on the pistons(since I had the bleeder cracked).

Mystery solved. If you don't believe me then try it for yourself next time you bleed your brakes.

I bled the brakes out with some Prestone DOT 4 in the following order:

(2)LF - RF(4)
...|xxxxxxx|
...|xxxxxxx|
...|xxxxxxx|
...|xxxxxxx|
(3)LR---RR(1)


Or spelled out plainly: Right rear, then left front, then the left rear, then the right front.

The pedal feels amazing now by the way... I really didn't expect to feel a super noticeable difference since it's only an 09 model year with only 36k miles.


I will add that in all reality, the order that you bleed the brakes in does not really matter... as long as you bleed one circuit entirely before starting on the other. I think the "start at the line furthest away" think is mainly so you fill the longest line with fresh fluid first.





One more thing to add: If you think you have air bubbles remaining in the system, one -slight- modification to the bleeding procedure above can be done to aid in forcing the air bubbles past high spots.

Tell your helper to let the pedal up, then you open the bleeder... instruct them to STOMP on the pedal as hard/fast as they can, and hold it to the floor(do NOT allow it to come back up)... then you close the bleeder. I tend to do this once or twice after the fluid "appears" good at each wheel to make sure there isn't anything trapped that I don't know about... then finish up with one last "pump" with the typical method above. Neither method will introduce air into the system, it's just what I happen to do.

 

[molex7]

did this method on my mazda2 as you suggested, AMAZING brake pedal feel. Thank you so much for the write up

 

[xxxmonoxidechil]

Yup, Most Mazda's since the 80's or 90's have been this way. All 4 of my current Mazda's have to be bled this way. Ive actually had arguments with 626 guys over it.

 

[flatlander937]

did this method on my mazda2 as you suggested, AMAZING brake pedal feel. Thank you so much for the write up

No problem! Glad it helped!

Yup, Most Mazda's since the 80's or 90's have been this way. All 4 of my current Mazda's have to be bled this way. Ive actually had arguments with 626 guys over it.

Yeah, a guy I work with was PISSED when he couldn't get some car to bleed out right and had a crappy pedal after like 4 bottles of brake fluid. I got his comeback and had it sorted after 30 minutes.

 

[L3vzoomzooom]

Nice write up. I use a vacuum bleeder myself, since I don't have a helper most of the time.

 

[concept]

NEVER, EVER PUMP THE BRAKE PEDAL TO THE FLOOR! You can easily damage the master cylinder piston seal by doing so. This warning was included in a Popular mechanics article, a while back. They recommended that before you manually pump the brake pedal, you place a block of something under the pedal to limit the MC piston travel. Over time, the piston and seal wear a very slight step in the MC bore. By pushing the brake pedal to the floor, you can damage the piston seal by forcing it to travel past the step.
Newer vehicles and MCs may not be adversely affected, but as the miles pile up, so does the bore step height. I've seen this happen, so to be safe, use a positive pressure MC attachment bleeder or apply vacuum pressure to the bleed screws. Avoid the manual pump method unless you are prepared to replace your Master cylinder.

 

[flatlander937]

NEVER, EVER PUMP THE BRAKE PEDAL TO THE FLOOR! You can easily damage the master cylinder piston seal by doing so. This warning was included in a Popular mechanics article, a while back. They recommended that before you manually pump the brake pedal, you place a block of something under the pedal to limit the MC piston travel. Over time, the piston and seal wear a very slight step in the MC bore. By pushing the brake pedal to the floor, you can damage the piston seal by forcing it to travel past the step.
Newer vehicles and MCs may not be adversely affected, but as the miles pile up, so does the bore step height. I've seen this happen, so to be safe, use a positive pressure MC attachment bleeder or apply vacuum pressure to the bleed screws. Avoid the manual pump method unless you are prepared to replace your Master cylinder.

Eh I've heard this before but frankly in the 9 years I've been doing this(guessing 250-300+ times bleeding brakes at least?) I've yet to see it happen.

It won't hurt to put a block of wood under the pedal to limit travel though when bleeding.

Vacuum bleeders suck. Positive pressure bleeders(like Motive) are awesome though(thumb)


Honestly if you think about it: most drivers will not ever stop that hard aside from some panic stops... If a step built up enough to cause problems, then if someone took a REALLY hard stop they would accomplish the same thing and damage the MC/experience a failure. Frankly I'd rather find out while bleeding brakes at 0mph.

I'd be more worried about using a MC if the fluid had been 5+yrs old or 60k+ miles having never been flushed... Pitting of seal surfaces from moisture in old fluid will cause problems and could certainly cause this to happen.

When I'm on a laptop I'll add the bit about the wood under the pedal to the original post as its at least worth knowing about the possible risk.


One more thing to add while I'm thinking about it: most cars with ABS require an ABS bleed if air gets to the ABS pump(and technically is recommended after manually bleeding the brakes), you use a scan tool to activate the pump and it tells you to stand on the pedal... And it goes to the floor and pumps back up several times. FYI.

 

[concept]

Gravity bleeding is another (time consuming, but effective for older vehicle brake systems) method that has also been used by many, including myself, but I agree, pressure bleeding via attachment of feeder and pressure connection to the MC is the best way to bleed brakes. I wish I still had that Popular Mechanics issue, but I remember it, very well.
Even when you panic-stop, your brake pedal should not go to the floor unless there is air or a leak in the system. Especially with a vehicle that sees lots of stop & go miles on it, you are playing Russian Roulette by pumping the pedal to the floor when manually bleeding the brake fluid.
I've seen quick and gradual degradation of the MC piston seal, over the years. This is why when I do have the fluid flushed, I make sure the mechanic does not use the manual method.

 

[flatlander937]

My point was just that in a real panic stop it will ride beyond the normal travel(true not all the way to the floor) but still over the step/lip that is formed.


I think it's a bit silly to say its playing Russian roulette by bleeding the brakes like... Everybody basically.

If running beyond this step you're suggesting that any time a wheel cylinder(super common) or caliper fails, you have ruined the master cylinder which is crazy.

Again I've yet to see this happen.. Its not even a remotely common problem. If you want to limit pedal travel while bleeding then have at it. I personally feel its silly, and if the master fails when bleeding(which in 9yrs of actually working on cars I've NEVER seen), it should probably have been replaced anyway.

I think I will ask for a Motive bleeder for Christmas though, my wife hates helping me bleed brakes and my son is too short

 

[concept]

Here's an abbreviated version of the Popular Mechanics article:

http://www.popularmechanics.com/cars/how-to/maintenance/4213448

In the original article, they explain more about the "block" in detail. I asked a couple of mechanics about the reasoning and they both agreed that is always good practice to limit the pedal's travel when bleeding brakes. Both shop owner's use the pressure bleeder for that and time efficiency reasons.

As I mentioned, it is less of a worry when your MC is newer and more of a worry when the MC has many actuations under its belt.

 

[L3vzoomzooom]

Eh I've heard this before but frankly in the 9 years I've been doing this(guessing 250-300+ times bleeding brakes at least?) I've yet to see it happen.

It won't hurt to put a block of wood under the pedal to limit travel though when bleeding.

Vacuum bleeders suck. Positive pressure bleeders(like Motive) are awesome though(thumb)


Honestly if you think about it: most drivers will not ever stop that hard aside from some panic stops... If a step built up enough to cause problems, then if someone took a REALLY hard stop they would accomplish the same thing and damage the MC/experience a failure. Frankly I'd rather find out while bleeding brakes at 0mph.

I'd be more worried about using a MC if the fluid had been 5+yrs old or 60k+ miles having never been flushed... Pitting of seal surfaces from moisture in old fluid will cause problems and could certainly cause this to happen.

When I'm on a laptop I'll add the bit about the wood under the pedal to the original post as its at least worth knowing about the possible risk.


One more thing to add while I'm thinking about it: most cars with ABS require an ABS bleed if air gets to the ABS pump(and technically is recommended after manually bleeding the brakes), you use a scan tool to activate the pump and it tells you to stand on the pedal... And it goes to the floor and pumps back up several times. FYI.

I know Vacuum bleeders suck (insert pun here) but it's what I have, I would like to get the motive one.

 

[Goshawk]

Good writeup, been following your method so far - though I started the bleeding process with the opposite circuit (left rear, right front, right rear, left front).

Finished bleeding the first circuit (left rear/right front) without any hitches. Began working on the right rear, and there seems to be an inordinate amount of air in the system. I've probably pumped the pedal close to ~50 times, and there is still barely any brake fluid moving from the bleeder valve into the collection tube. There doesn't seem to be any drainage of brake fluid in the master cylinder reservoir either.

How would I go about trying to remove all the air from the system? Pumping the pedal doesn't seem to do anything, no fluid is being drained, and obviously the brake pedal has virtually zero feel to it with almost no resistance.

 

[Bloodstorm]

Eh I've heard this before but frankly in the 9 years I've been doing this(guessing 250-300+ times bleeding brakes at least?) I've yet to see it happen.

It won't hurt to put a block of wood under the pedal to limit travel though when bleeding.

Vacuum bleeders suck. Positive pressure bleeders(like Motive) are awesome though(thumb)


Honestly if you think about it: most drivers will not ever stop that hard aside from some panic stops... If a step built up enough to cause problems, then if someone took a REALLY hard stop they would accomplish the same thing and damage the MC/experience a failure. Frankly I'd rather find out while bleeding brakes at 0mph.

I'd be more worried about using a MC if the fluid had been 5+yrs old or 60k+ miles having never been flushed... Pitting of seal surfaces from moisture in old fluid will cause problems and could certainly cause this to happen.

When I'm on a laptop I'll add the bit about the wood under the pedal to the original post as its at least worth knowing about the possible risk.


One more thing to add while I'm thinking about it: most cars with ABS require an ABS bleed if air gets to the ABS pump(and technically is recommended after manually bleeding the brakes), you use a scan tool to activate the pump and it tells you to stand on the pedal... And it goes to the floor and pumps back up several times. FYI.

@flatlander937 What scan tool works with the mazda3i? I've got a 2008 and I believe it has air in the abs pump.

 

[damaster]

Does this method and order of bleeding the calipers also apply to a 2011 CX-9?