brake booster, or master cylinder

[shfaster]

sup everyone, i have a 94 honda civic. i'm having trouble with the brakes. after searching through the forums, i have found that it to be either my brake master cylinder or brake booster. according to one of the forums, if my car is off, and i pump pump pump the brakes, if it gets hard then my master cylinder is good(and it does get hard when my engine is off). but when i start up my engine, the brakes go down more than 1.5 inches in all the way to the floor. i have no leaks in fluid. is this test accurate in determining the problem to be the brake booster since the breaks get hard after being pumped when my car is off. thanks.

 

[deth101]

straight out of helms;

Functional test
1. with engine stopped,depress the pedal hard and hold that pressure for 15 seconds.If the pedal sinks,the master cylinder,brake line or a caliper is faulty.
2.start the engine with the pedal depressed.If the pedal sinks slightly,the vacuum booster is working.If the pedal height does not vary,the booster or check valve is faulty.

 

[TWISTEDIMAGE]

good answer

 

[shfaster]

ic. what if the pedal sinks alot (almost to the floor) after i start my car. i've already replaced the master cylinder (i made sure to bleed the master cylinder proplerly before i put it in), and i still have the same problem. i don't think there are any leaks in the brake lines because im not losing any fluid. i'll try bleeding it again a few more times, and i'll double check to make sure i have no leaks. i'll keep trying different things and update u guys, in the meantime if anyone has any advice it would really help.

 

[reckedracing]

you're pumped it up and held FIRM pressure on it and you get no drop at all?
but when you start the car it will drop?

i would just sit there with the car running and pump the brakes for a good 5 minutes on dry pavement, then inspect under the car completely...

if you already replaced the master cylinder then my guess is that you have a leak or some serious air thats being compressed when you start the car...

how about this...
how many times do you need to pump it to get a firm pedal?
it takes a long ass time to get the air out of the system when you change the master
get one of those fancy bleeders, or take the time, start from the passenger wheel and work your way from the furthest brake, to the nearest brake in respect to its position on the car to the position master...

 

[shfaster]

hey all. Thanks alot for your help. my brakes are working perfectly now. i rebled it again doing it the right way this time instead of taking the easy way out. i didn't bleed it the proper way doing all 4 sides the first time. i didn't know not bleeding it the proper way would make such a dramatic difference on the way the brakes worked. thanks alot for your help.

 

[reckedracing]

i hate to ask this but what way did you bleed them thats the wrong way??
lol

 

[shfaster]

Originally posted by reckedracing@Mar 23 2005, 06:14 PM
i hate to ask this but what way did you bleed them thats the wrong way??
lol

[post=477708]Quoted post[/post]​

i figured i only need to bleed the system from one place since one fault in it can cause the entire system to lose pressure, i figure one spot will be enough to get the air out.

 

[reckedracing]

well, congrats on having good brakes again