break failure HELP!!!!!!

[jarhead76]

for the last 3 days the breaks have been acting up. they work fine for a wile then at random i louse break pressure. i pump the breaks and it come back problem. then tonight i lost all pressure and almost went throw a busy intersection. scared the heck out of me. i was able to stop thanks to a working E break (if you did not read it or don't remember i had talked a bought it on another post a few weeks back). I'm not loosing flowed and the lines although old are not collapsing as far a i can tell. 

has any one had this problem if so any pointers where to start.

[bd]

Have you checked the fluid level in the master cylinder?

Visually verify there's no leakage from the lines or any of the wheel cylinders, calipers, etc.  If everything is dry, but the M/C is empty, unbolt the M/C from the booster and slide it forward enough to inspect the M/C piston and bore - if it's wet with fluid, you found your leak and will need to replace the M/C and possibly the booster.

If the M/C is just low on fluid, check the pads and lining for excessive wear.  It may be time for a brake job, adjustment and bleeding.

[jarhead76]

there is no leak in the system sorry forgot to say that.

[werewolfx13]

All three of my brake failures on my '83 were the m/c leaking from one cylinder to the other resulting in no brakes....first time, it did what you were describing (pump the brakes and they work fine), the next two were just sudden failures....I've gotten *really* good at replacing master cylinders when its below freezing..never has happened when its warm out.

[VileZambonie]

Stop breaking your brakes 

[diphthong]

This sounds like a temporary bypass in the master cylinder,  It's incorrect to think once the master develops a blow-by or other wise know as a bypass, it  can ever again build sufficient hydronic pressure to apply the brakes. 

Not only is this incorrect thinking but it's dangerous. As a brake and front end mechanic, I've seen this more then just a few times.  Two come to mind, once on a test drive for check brakes, I had good brake pressure, enough to know at least one wheel on each axle were metal to metal. But then came close to having an accident pulling on to the hoist because of a total bypass.


The second was a temporary bypass in a clutch master.  Test driving my cousin's corolla for what she called a "non-stopping problem." At a stop light the clutch master completely bypassed sending me into the intersection.

So, if the system isn't USING fluid and you lose brake pressure, what else can it be other then a by passing master?
Think about it, if the break pedal travels any in a sealed (non leaking, air free) hydraulic system, it either has to be moving  the pistons in the wheels cylinders, or there really is not pressure being created by the travel of the break pedal i.e.  the master cylinder is defective, or in other words, the bypass of fluid by the pistons in the master is essentially the leak.

Like my wife says, it's either chocolate or vanilla.


safe wrenching...


 



I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)

[roundhouse]

Replace the MC.  Its easy.  And only a few dollars
Be sure to use the special tubing wrench  for brake lines
A normal open end wrench will almost always slip off the nut

And bench bleed the new MC before you install it
Also.  For those of you that bleed the brakes on an older vehicle.  Put a wood block under the brake pedal do it can't go down any further than normal

If while you're bleeding the brakes the pedal goes all the way to the floor it allows the piston and o rings in the MC to travel across the part of the cylinder that they have never touched       That part of the cylinder is rougher and will damage the o rings.    In a few weeks your MC will be bad

I'd replace the rubber flex hoses and maybe pads too

 THe rubber flex hoses also get swollen on the inside
They look fine. But are not   And the only way to know is slice them open

Also to anyone else reading this
When the brakes first start acting weird.  Get it checked out.   They are not magically going to get better again
   They will get worse until you crash
Usually failing at the most in opportune time

[Dan75k20]

Master cylinder my k 20 has the same issues changed the master and it was fine

[thirsty]

For those of you that bleed the brakes on an older vehicle.  Put a wood block under the brake pedal do it can't go down any further than normal

If while you're bleeding the brakes the pedal goes all the way to the floor it allows the piston and o rings in the MC to travel across the part of the cylinder that they have never touched       That part of the cylinder is rougher and will damage the o rings.    In a few weeks your MC will be bad

I know this is an old thread but... roundhouse have you had this experience? If so, more than once?
I get the theory behind what you are saying but I have done hundreds of jobs that require bleeding the brakes and have never had a M/C fail because of letting the pedal go to the floor. Seems to me that the only way the cylinder could get rougher is if there is moisture in the fluid and then you are going to have other issues also.

I'm not saying you are wrong, I'm just wondering if you have had first hand experience with this because I never have.

[VileZambonie]

It's true, you will see more common MC failures after the system springs a leak.

I don't agree with putting a block of wood under the pedal when bleeding the system. If the MC can't take it then time to replace it. Better to find out when you're anticipating it.   

[roundhouse]

It won't cause the MC to fail immediately , but it can significantly shorten the life of it, causing alot of extra wear on the O rings when the O rings travel past the spot where they have always stopped at for the last several years

Not a real big deal on a squarebody since every auto parts store has a rebuilt MC and most have a brand new one available for an extra $20

Bu if you're working on a 39 Studebaker or a 48 Nash
You ain't running to the auto parts store to get a $30 replacement MC .



Every brake system has some water in it

I've just gotten to the point now where if I do major repairs on the brakes of an old car. I just replace the MC ,( with a brand new one if I can find it, the rebuilt ones are not high quality rebuilds, usually done in mehico )

Saves time because almost every time I've had to bleed the brakes on an old car and start driving it , a few months later I'm replacing the MC because the brakes get soft and no amount of bleeding will firm it back up
I knew it was an old thread but I've had to replace the flex lines on every GM truck I've ever had that was more than ~15 years old    I think it's the clamp that holds the flex line about half way down

When I had to replace em on a 82 C-10 I sliced the lines into sections.  About every inch or so.  And sure enough in the spot where the clamp prevents the line from flexing it was swollen closed inside

[Irish_Alley]

round had the same problem in my 94. the mounting bracket on the brake hose rusted on the inside causing it to squeeze the hose to the point of restricting it and causing the brakes to lock up on that side