Hello everyone
I've a 2000 Accord 2.3 LX. My question is will a brake booster that has fail will cause a brake system to start failing.
I have bleed the brakes not able to get all the air out of the system and replaced my master cylinder (bleed all the air out before installation) Still not able to get the air out of the brake system.
There's no leaks, my brake booster has a hard pedal when the engine is off and the pedal goes down when engine is turn on. What can be my problem?

 

With the engine off the booster should be able to store 2-3 full stroke assists before losing assist. Then the pedal should become firm. With foot on brake pedal and starting the engine, the pedal should then drop down. But not by much. If the pedal is flooring then there is either a fault in the MC or air is trapped in the system still. If the system looses assist from the boost as soon as the engine shuts off, then it may be that the check valve in the vacuum line to the brake booster is faulty and not holding vacuum after engine shut down.

You stated you have air bubbles when bleeding.
How are you bleeding the brakes?
If using a vacuum pump, unless the threads of the caliper/wheel cylinder have yellow teflon tape(gas tape) on the threads, anything above 10inHg will cause air to be sucked past the bleeder nipple threads which will give you multiple bubbles. This takes up space and you lose pressure which in turn makes it take longer to bleed. I also would not go much more than 15inHg during normal bleeding. On older systems I have found this will cause the wheel cylinders or even MC to suck air.

 

Yes, when I shut the car off the pedal thus have 2-3 strokes and then it becomes firm. When I start the engine the pedal drops to the floor. So I could have a faulty brake booster, will that cause air in the brake system?

When I bleed the brakes I start from the LF, RF, RR, LR in that order. I do see a lot of bubbles in the hoses whit the vacuum pump I'm using.

If using a vacuum pump, unless the threads of the caliper/wheel cylinder have yellow teflon tape(gas tape) on the threads, anything above 10inHg will cause air to be sucked past the bleeder nipple threads which will give you multiple bubbles.
This is what actually whats happening. I think I'm going to get a helper and do a manually bleeding.

 

This is normal operation. The brake booster is functioning fine.

Just use some teflon tape or heavy grease around the threads to prevent false air leak.

I would suggest NOT using the two man, manual brake bleeding method.
On an older master cylinder, if you floor the brake pedal or overstroke the pedal(from normal throw) the seals inside the MC will ride on the unpolished bore of the MC. This can damage the seals and fail the MC. MC may not fail right away but it will. You would need to prevent the pedal from overstroking or risk damage to the MC, a 4x4 woudl help, but you would still need to make sure the pedal is not traveling further than normal. And your partner in helping would need to understand this and not remove the block while pumping.

 

Ok I'll try to keep using the vacuum pump with teflon tape around the bleeder tip.
Also, (history) the vehicle was sitting for 6 months in my driveway with a bad starter, alternator and battery, after I fixed the problems the brake pedal hit the floor as where I'm present with this problem. Could my pushrod be to short where the brake pedal is to low now?