2014 Mazda 3, 101k
When compressing a brake caliper piston, is cracking the bleeder screw absolutely required? Or is it better to open the master cylinder and remove a bit of fluid before compressing the caliper? Or is it okay to compress while everything is closed?
Honestly I think it depends on the car. All these new ones want you to use a computer to disconnect the parking brake and all that before doing the job and pushing the fluid back to reservoir is like a big no-no for the new systems as the computer gets confused and then you would have to "resetting the system" unless you unplug the dang car first from my experience lol. For any older car I just use a cloth and channel locks and that does it easy lol. For your Mazda is has that rotation compressing caliper right? For that reason I would just crack the bleeder, makes it a little easier and not really much cleanup tbh. But if you just wanted to compress it just remove the excess from the tank and you should be fine. After that it's all up to preference.
Side note: if for whatever reason when you compressing the piston of the caliper and back peddle a little it could introduce air into the system if the bleeder be cracked. So that's another reason to not crack the bleeder unless you were trying to do a full bleed of the system after the job anyway.
I don't understand the bleeder screw thing. With brake pedal released, the master cylinder just passes fluid straight through to the reservoir.
I probably should of added "when installing new brake pads."
I know
Concern about ABS module, I reckon.
what about it?
There are definitely two schools of thought on cracking the bleeder. I never have and so far have had no problems. Others say that compressing the pistons without opening the bleeder forces contaminants into the ABS, which can damage the valves. Some also say that excess pressure going back toward the ABS can be harmful. Scotty used to be in the no bleeder camp but now he says open them. Could be that some ABS modules are more sensitive than others. Damned if I know.
> forces contaminants into the ABS
explain how there is contamination everywhere except in the ABS, and somehow it gets in there when I compress the caliper, but not the brake pedal. How does contamination "damage" the metal valves.
> Some also say that excess pressure going back toward the ABS can be harmful
What excess pressure? Nobody has thus explained to me where this pressure comes from.
Squeezing a piston in faster than it would retract?
The ABS system pulses the brake a many times per second. I don't think I can do it by hand faster than that.
See below:
https://carkiller.com/scottykilmer/qa/2010-ford-taurus/
And at 2:45 below:
https://m.youtube.com/watch?v=qjVRk8abvOc
That makes absolutely no sense to me. The video doesn't explain anything.
The fluid will go back into the open reservoir. There's no way for pressure to build up.
Besides, there's massive pressure every time you step on the brake! There's probably more pressure in the system when you're braking, then pressing in the caliper piston!. Think about putting all your leg muscle into a 1ft long lever, which drives a long stroke piston. It's nonsense.
A brake master cylinder for those who aren't familiar:
Show me where pressure can build up.
Definitely a good discussion and I am trying to understand Scotty’s recommendation. As usual, you make excellent points. The best that I can gather is it’s not the pressure we are worried about but rather the possibility of sending debris back the other way to the ABS module and causing issues - and perhaps some units are more delicate/sensitive to others? This is what I found:
https://www.brakebleeder.com/preventing-damage-abs-modulators-brake-pad-replacement/
I still don't buy it. If the system was that sensitive to debris, then it would fail every time the ABS activated, because the pulsation would kick up a maelstrom debris.
I always just pop the hood and take the cap off of the fluid reservoir. I've never had a problem doing it this way.
me too