Anonymous asked in Cars & TransportationMaintenance & Repairs · 9 years ago

When to bleed a master cylinder?

I need to bleed my brake system. Do I need to bleed or bench bleed the master cylinder as well. Every article I have found on the topic begins with some variation of "If you install a new master cylinder..." I am just bleeding the brake system, not replacing the master cylinder. I have found no information on whether bleeding the master cylinder is a necessary step for this process.

4 Answers

  • Stu
    Lv 7
    9 years ago
    Favorite Answer

    If you have a "spongy" pedal, replaced a line, wheel cylinder or "opened the system ANYWHERE, it is important to "bleed" the entire system. If the air (you are trying to purge is at a remote wheel and NOT at the master cylinder, it may STILL be necessary to "bleed "the master cylinder anyway.

    Actually, it is a good idea anyway, AND remember that you could have drawn AIR into the cylinder if your pedal ever went to the floor (pushing all the fluid out of it and you pulled the pedal back up without the resevoir "topped up with fluid". It is good to "flush th system" with NEW fluid, and pump the pedal till you get some pressure, and have someond hold the pedal down as someone briefly opens and closes each wheel cylinder valve. It is CRITICAL that you KEEP this Cylinder Topped with fluid at all times, and keep pressure on the pedal everytime you open any valve or you'll be sucking MORE air into the system.Essentually, you will be "bleeding the master cylinder" as you pump and HOLD the pedal (provided you MAKE sure there is plenty of fluid in it. The idea is to get the air out of the system wherever it travels, and it will go wherever it can find a way out?or IN!

    Once you can't get ANY air out from the wheel cylinders, or AT the master cylinder, and you have a consistent "HARD PedaL", you are done. Yes way or another,you should purge all air from the system, and the master cylinder is part of it.AS you should de ADDING new fluid anyway, you SHOULD include the Master Cylinder in the process. I hope this answer gave you a "BRAKE". Peace.

  • Anonymous
    9 years ago

    If your just bleeding the brake system, you shouldn't have to bleed the master cylinder. It's all one big happy system. Just bleed the brakes as you normally would by pumping the brakes till it's hard to push, then open the bleed port till straight fluid comes out. Be careful to not run the system dry otherwise you will have to bleed the master

    Source(s): Mechanic for 20 + years
  • The only time you need to bleed the system is when one of its components such as a caliper, wheel cylinder, brake line or master is replaced, other than that trying to bleed the system just leads to more questions on YA as to why don't my brakes work and how do you bleed them,

  • rieves
    Lv 4
    4 years ago

    Is fluid coming from the thread of the bleed nipples or only from the hollow on the top? in spite of if it somewhat is you have them loosened too plenty, it is likewise properly worth putting a dab of petroleum jelly on the thread earlier you insert new ones to maintain a good seal. it might purely be loosened via some million/2 a turn – to make the job much less complicated use a one guy bleed kit with a sparkling pipe and a one-way valve – good up the fluid reservoir, pump the lever, fluid ought to come from the bleed nipple into the sparkling pipe and out right into a jar, as quickly as there are no longer any air bubbles showing in the sparkling tube, tighten the bleed nipple (no longer too tight) and seal the reservoir. in the time of this technique you're able to desire to maintain an eye fixed on the reservoir, do no longer enable it get extra suitable than a million/2 empty, as quickly as you have tightened up the bleed nipple and adjusted the reservoir cap you ought to get some stress – in case you do no longer, faucet the joints and bends of the brake hose with a spanner (no longer something too no longer elementary) it might reason any ultimate air bubbles to commute as much as the reservoir. If that fails, placed the motorbike someplace thoroughly dry, do away with the reservoir cap, tie decrease back the brake lever with a rubber band and pass away it in one day – it must be dry and airborne dirt and mud unfastened, brake fluid will entice moisture and which will smash its overall performance. And, bear in mind constantly use a clean bottle of brake fluid, if it somewhat is been opened for any length of time it somewhat is going to be ineffective.

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