We bled the brakes after replacing the 4 brake hoses that run to the calipers since a hose burst the other day. We bled them, and the brakes still feel spongy and the fluid is decreasing ever so slightly, making me think the master cylinder has gone(we rebuilt the calipers).

Can someone tell me;

  1. How do I bleed the master cylinder for the first time without screwing the new master cylinder up?
  2. How can I check the brake booster to see if fluid has gone into it without removing the old m/c (because I need to drive it like 2 times before the new one comes)?

My assumption is that if that nasty fluid gets into the booster the rubber seals or whatever in there a goners, and that’s fine because I can get a new one at a wreckers but I just want to know before I remove the old one if any leaked inside so I know what to expect when I pull it apart.

  • Did you bleed the existing master cylinder? Check all the metal lines for leaks? Also, I edited your question to be easier to read and removed the question about purchasing a certain brand (that is off topic). If you disagree with my edits, you are welcome to revert the edit.
    – CharlieRB
    Commented Nov 3, 2017 at 11:54
  • Well I included the brand because it was the cheapest on rock auto and wanted to know how reliable it is Commented Nov 3, 2017 at 12:05
  • Doesn't matter. Asking for purchasing advice made it off-topic. Sorry.
    – CharlieRB
    Commented Nov 3, 2017 at 12:34
  • What car is this? Does it have ABS because that needs to be bled separately, normally with a computer.
    – JPhi1618
    Commented Nov 3, 2017 at 19:25
  • Yeah it has abs but it’s disabled because one of the sensors went, im replacing that later. 1995 Acura legend Commented Nov 3, 2017 at 19:30

1 Answer 1


As another user mentioned, you will need to be absolutely sure that fluid isnt leaking from any other location at all. If the hose burst caused the current cylinder to empty out, you will want to try a bench bleed, also as suggested, followed by rechecking all of the calipers for air. To check for fluid in the booster, you could try a wire hanger, or perhaps even your oil dipstick after wiping it off well, pull the vacuum hose off, and carefully stick that in to the bottom. If you pull it out and see any fluid, there's your answer, in which case I would replace it. You may be able to remove the retaining bolts to the booster and carefully pull in away a little bit to confirm a leak there, but if there's too much resistance, don't force it. If that's the case here, and a new master cylinder is needed, a bench bleed is necessary before installation. It may come with a bleeder kit and, if not, you may purchase one. Finally, rebleed the rest of the brake system to be thorough. If you haven't already flushed out the old fluid, now's your chance. You may as well do it. API is obviously aftermarket, which always runs a bit more of a risk of receiving a defect out of the box, but compared to other aftermarket brands, it's just as competent (in my humble opinion), though I would be careful bot to damage it during the bench bleed. A bench bleed is basically just connecting transparent tubes to where the two lines will connect and running them down into a container filled with some fluid. The whole process is A LOT easier with a vice. You'd fill the reservoir with fluid, depress the piston on the cylinder and watch the air bubbles work their way out. Pinch the lines tightly as the piston retracts and repeat this process until you see no more air. There are plenty of videos, online tutorials, etc. to assist you with this if you're more of a visual type of person. Lastly, if the new master cylinder doesn't come with the reservoir, obviously you'd move the old one to the new one. Good luck.

  • Perfect answer!!!!!!!!!! Commented Nov 3, 2017 at 12:50
  • And thanks for the info on API, I was wondering if it was less competent than other brands because of its price, and I couldn’t find their website Commented Nov 3, 2017 at 13:31
  • Thank you. Hope it helps and I wish you the best of luck. Let us know if you have any more questions. Commented Nov 3, 2017 at 14:07
  • Try to break your answer into paragraphs to make it easier to read. The "wall of text" is hard to look at.
    – JPhi1618
    Commented Nov 3, 2017 at 19:27

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