Xeros

Okay so I bled my Brake master cylinder then i bled all of the slave cylinders. Intrestingly enough I go back to minutes later to bleed the slaves and they are all full of air again. So does this mean I have a bad BMC? And no there are no leaks of fluid anywhere. I took the damn thing off about a month ago to inspect it it looked fine. So bad BMC causing air to go into break system or somehtin else?

mad_7tist

1. how did you bleed the master?
2. there will be alot of air in the lines if the master had air and you pumped it with the lines closed

a quick way to bleed the master , if it was not bench bleed, is just barely crack the lines off it. have someone slowly press the pedel down. before they release the pressure close the lines and repete. sometimes it just takes a Long time to get the air out. do it in series starting at rr,rl,fr,fl

user 9348703

Xeros---did you change some parts or just?

dorifc3s

u can use an nissan S-14 240sx brake master cylinder. it fits, and everything and u just have to bend the lines... its an upgrade i think, the pedal is shorter and smoother.

Xeros

No I took it off a lont tiem ago when I was rebuilding the entire car. I got a little kit to bleed the BMC. All you have to do is attach 2 nipples to the place where the lines are on the BMC then route two hoses into the resivoure it self and than pump untill there is no more air in the system at all. One of the guys here on the forum recommended it.

mad_7tist

another test is when yo come to a stop the brake pedel should get hard and stop the car at one point. if the pedal goes down the MC is bad. but it may take alot of time to get all the air out. when you bleed the brakes is there air in the system again?

Xeros

yeah.
Instantly.
I would finish off bleeding one and then all of the sudden I would go back and just check quickly and there it was air again instantly...So its a bad BMC i take it aye?

Mahjik

iTrader: (1)

How are you bleeding the brakes?

Are you using a Power Bleeder? Do you have speedbleeders installed?

Xeros

Good ol tube to bottle with water and a 8mm wrench. I would like to get some speedbleaders though.

maxcooper

I would use brake fluid in the bottle instead of water -- you don't want to accidentally suck any water into the brake caliper.

Just to verify:
1. All bleeders are closed.
2. Person A steps on brake pedal and holds it down.
3. Person B loosens one bleeder screw, fluid (perhaps with some air) comes out, closes bleeder.
4. Person A takes foot off brake pedal.
5. Go back to step 2 until fluid comes out clean and air free in step 3.

-Max

Xeros

yeah um have done that one tooo many times now.
In all seriousness. WHAT THE HELL! Like I said I would bleed the RR,RL,Fr and just before I moved onto the FL I would go back to the RR to check it and all the sudden there was air in it again just after bleeding all of it out.....And if it is the BMC where the hell is all that god damned fluid going? There isnt a leak in sight!!! Please help.

Xeros

The pedal also feels spungier the more I drive and brake each time. Where is all this aircoming from and fluid going ?

user 9348703

slave and master can both suck air.

I would say change the slave first "ITS CHEAPEST" or overhaul it if the cylinder is good, IE no corrosion/pitting on the inside of course.

Also since it sounds like the car was sitting without fluids for a while, well the slave rubber can dry up and crack pretty easily..

Xeros

I am correct to assume when we say slave cylinders we are talking about the brakes right? Becasue I have been looking over the diagram of the braking system and it shows nothing more then master cylinder stuff but only bleeps a word or two abou tthe slaves which pretty much sounds like the brakes them selves, or am I totally off?

Mahjik

iTrader: (1)

When my MC failed, I had no brakes at all. Are you bleeding your brakes by yourself or with help?

As Max mentioned, I wouldn't use water in your bottle.

Xeros

I'm definitely getting help from a friend.. He pumps the pedal and I bleed.

poorboyracing

Mike Nola

Turn the ignition switch to Run while you are bleeding the brakes...

You are checking the fluid resevoir to ensure you are not running out of fluid and sucking air arent you?

Xeros

Yes the car is on while I bleed and yes i am making sure tha it never even gets bellow max ahahaha. Majik said when his went bad his breaks didnt work period. My gradually fill back up with air. Where coudl this be coming from?

Xeros

I wonder, is it possible for one of the calipers to leak in the air by any chance? I noticed that my FR caliper was taking for ever and ever to bleed. It doesn't leak any fluid though....

Xeros

Alright just went back to bleed the BMC out of curiosity with the car on.....And here is what happened. The BMC woudl bleed out and the pedal woudl feel a lot stiffer again. then I gave it liek 3 seconds and all the suddon it was full of air again. So...is this the BMC or is it the power break unit behind the bmc that revieves all that air from that one vacuum line?

DaleClark

iTrader: (55)

Few things -

First off, bleeding brakes is a BITCH. No way around that.

How many miles are on your car? Most brake master cylinders are good for around 120,000 miles or so before they start to fail. If your car has a lot of mileage, it might be wise to look into a replacement. I don't think they're THAT pricey, but I haven't really priced FD master cylinders - FC masters are around $60-80. Do NOT try and rebuild it - get a quality new part, trust me on this one.

That said, a bad master cylinder will either do 1 of 2 things. Either it will internally lose pressure or it will leak externally. External leaks can be from the back of the master cylinder where it meets the brake booster, and it drips down the brake booster, or a leak from the reservoir itself, as sometimes the rubber grommets around the plastic nipples of the reservoir fail and have a slow leak. Internal leaks are pressure getting by the hydraulic seals inside the cylinder - that will give you continually mushy brakes and can be hard to diagnose, as it's very similar to just having air in the lines.

If you can get a set of Speedbleeders, that makes life a million times easier. http://www.speedbleeder.com you need 2 SB8100's and 2 SB7100's. This makes bleeding brakes almost fun . Crack open the nipple, hook up the reservoir to the nipple, and pump the brakes slowly until you have no bubbles.

I've never heard of using a 240sx master cylinder, but some use the 929 master cylinder as an upgrade. This is typically only needed with large calipers that have more volume and require more pressure for a good brake feel.

Dale

Xeros

Alright I will just have to go and order a brand new one I think becasue it has absolutely no leaks anywhere out side of it. Not down the breke booster nor the reseivoir. If it really is the internals I should proabably just go ahead and get a new one right? it has about 60300 or so miles on it now. And I was just recently lookin at the speedbleeders becasue I am pretty damn tired of having to wait for a friend to be around and help me out! think I'll buy some when I order the BMC.

DaleClark

iTrader: (55)

At 60,000 miles I doubt your master cylinder is bad. Unless when you had it off the car something bad happened to the master.

I'd get Speedbleeders and bleed 'em again. Also make sure none of the lines in the system have leaks - even a slow leak can allow air to be sucked into the system.

Dale

Mahjik

iTrader: (1)

Just FYI, when I replaced mine over the summer, I was told there were no new MC's anymore. They are all rebuilt ones. You can get one from Malloy for under $100 with sending back your bad/damaged MC.