Your brake booster may be fine. The seal between the master and booster is bad causing the hissing at the master. This bad seal will also allow the pedal to rise when the vacuum source is removed (engine stopped). The main reason this seal would be bad is if someone replaced the master or booster without putting a new seal in.

The pedal sinking when holding the brakes on is either a bad master cylinder or a leak in the system (possibly at the master).

Are you loosing brake fluid? If yes then it's a leak and could be at any of the calipers or the end seal on the master. If you can't find signs of leaking at any of the calipers a likely leek location is the end seal of the master letting fluid escape into the booster. If you are not loosing fluid then it's a bad master leaking from one internal chamber to another.

The surface rust stream is probably caused by this or a previous master leaking fluid out the end seal. One thing to watch for when replacing such a bad master is to see if there is any brake fluid inside the booster that would brake down the diaphragm in the booster over time.

Mike

 

Thanks for the info. I'll order a seal tonight, and maybe a master, not sold on it being externally leaky, because i've had the car for about a month now, and bled the brakes the first weekend i had it. the brake fluid was up to the max line when i got it and was dirty (brown and murky). As it sits now, the fluid is still at max level, and I've never added any.

the leak between the chambers seems likely to me, because wouldn't that make the pedal softer as well? the car has some pedal feel, but it seems like it wont be long that it wont. i can't pump the pedal to build up pressure after the pedal has fallen, i have to let it come up on its own, then it is fine.

The MC doesn't look like it has ever been replaced, judging solely on the condition of the alum. cylinder compared to the rest of the engine bay alum. and the amount of rust on the reservoir clamp. I'll disassemble the thing this weekend and check it out. Thanks a lot. b

 

replaced that seal, but not the MC or brake booster, brakes feel much better. the pedal position no longer changes at a stop, or with the engine off, and no more vacuum noise. Thanks yall
-- Edit --

Added pic,

New seal on left, Old on right

 

having problems on my brakes and since we in the topic ok so changed to the pads on my rear disk after that put it back together and the brakes didnt lock even when i bled the brakes heard that i was suppose to do it to all of them and after messing with the front ones to bleed them they didn't lock either when i hold the brake pedal u could feel it going in little by little what could it be im not leaking any brake fluid cause checked and hasn't gone down still same spot any help?????????? thanx guys

 

lock, as in...lock up? do you actually want them to do that? did you do the bleeding in the right sequence ( it defies convention, i think its RP, FD, RD, FP) also, run through the diagnostics in the manual, and tell us what ya got.

 

wish i had a manual and i thought they where suppose to lock cause had a 91 dx and they used to lock also would hold the pedal down and wouldn't be able to spin it with a crossbar on my 88 its hard but then starts getting lose and could spin it with the crossbar and not by hand and didn't do it in that sequence did it from back to front

 

abridged from the manual
functional test
1. engine off, pump pedal, hold down pedal hard for 15 seconds, if the pedal sinks, a brake line, cylinder, or MC is bad
2. start engine with pedal down, if it sinks, booster is good, if not, brake booster or check valve is bad

Leak test
1. Depress and hold brake with engine running, stop engine, pedal height shouldn't vary for 30 sec. if pedal rises, you have some vacuum leak somewhere (thats what mine was doing).
2. with engine off, pump pedal, should get harder to pump each time, with a rising pedal.

check valve test
1. disconnect brake booster vacuum line at booster, start engine, vacuum should be available, if not, check valve is likely dead.

are you saying that with the car jacked up, wheels in the air, and someone pressing the pedal, you can turn the brake rotor with your hands? if so...yeah, you got some kinda problem there?

I just checked the manual for bleed sequence, and what I recalled was correct.

punctuation...is nice sometimes.

 

yeah cause when i bled each one they bled then stopped but then little burst kept coming out just when i think it has stopped and i sat there waiting over and over and just keeps going with pedal down might try some of the test and let u know wassup

 

If you push on the pedal and it feels decent, then while you hold the pedal down, it starts sinking to the floor, you have a bad master cylinder. That is the classic symptom of a bad MC. I've had that problem on both of my CRXes at one point or another.

Note that I'm talking about with the system all buttoned up, not with any bleeders open or anything like that. For me, it happened while I was driving and then stopped at a light.

--DD

 

good info thanks for the help gotta check rex tommorow morning dam rain