Scary, intermittent brake failure

[dave255]

95, 5sfe, 225000k, 4 wheel disk

So the other night I'm driving down a hill towards an intersection in a 50MPH zone when I attempt to brake for the upcoming red light. The pedal goes straight to the floor when I press on it and I receive no stopping power. My heart rate instantly triples as I figure my brakes are out. After pumping the pedal a few times, my brakes come back to life and I am able to stop before the intersection. At this point my house is about a half mile away, so I cautiously drive the rest of the way with no problems whatsoever. My brakes resume normal function, as if nothing had ever happened. It's late at night, so I go to bed and figure I'll tackle the problem in the morning.

The next day I do a complete visual inspection and see nothing out of the ordinary. The brake fluid level is fine. Nothing is leaking under the car or around the calipers. Brake lines look good. I've never installed a master cylinder or booster in my life but I have a pretty good understanding of how they work and saw no leaks from them nor anything outwardly suspicious. I also tested the brake booster with the operation and airtightness diagnostic checks described in the Haynes manual, which it passed. I take the car out for a cautious test drive and the brakes function 100% normally, as if nothing had ever happened. There were no symptoms prior, and no symptoms after. Just one isolated incident. The car has worked perfectly since.

As you can imagine, I am kind of freaked out that this could happen again. Has anyone experienced something like this before? Is this an early sign of something starting to fail, maybe the booster or master cylinder? I'm assuming air in the lines can't be the culprit because that would cause consistent squishy brakes, not intermittent, correct? Are there any other diagnostic checks I should perform? Any advice you can offer would be greatly appreciated.

[chronoti]

i would say bleed your brake fluid water in the the fluid can boil and cause failure kinda like what you said also look at the one way vacuum valve and change it could be starting to foul, it's like 2 dollars and give you a little more peace of mind

[fenixus]

Originally Posted by chronoti

i would say bleed your brake fluid water in the the fluid can boil and cause failure kinda like what you said also look at the one way vacuum valve and change it could be starting to foul, it's like 2 dollars and give you a little more peace of mind

+1

I would even go further and flush the brake system with 1L of fresh Valvoline DOT3&4 fluid. Mittyvac vacuum pump is very handy in 1-person bleeding/flushing.

OP must have a serious air pocket in brake lines if something like that happens.

[dave255]

Thanks for the replies. If I had an air in the brake lines somewhere, wouldn't that cause a constant squishy brake, not an intermittent one?

[fenixus]

well, there is a few more possible reasons. it might be old fluid and it tends to gain 1% of moisture/water with each year, so a few years old fluid will have a few percent of water in it which tends to turn into steam (which can compress easily unlike the fluid) under high temperatures occurring when you hit brakes.
lastly it might be also a sign of failing master cylinder.

first do either bleeding or flush the fluid to be sure it's not the cause then go from there.

I know how you felt, because i have lost brakes twice so far in my old ride ('92 buick lesabre v6). first time a rubber brake line burst in driver rear and was pissing fluid whenever i was trying to hit brakes (pedal was going to floor too, but there was no chance to "pump" it up as there was a leak).
second time a steel line for rear passenger side (connecting to a rubber line) burst under car due to rust. again pedal was going to floor and car was pissing fluid when i was depressing brakes and there was no way to pump it up (leak).

DIY Brake flushing:
DIY: 1996 Camry Brake Fluid Flush Procedure (GEN3)
I suggest all reading this thread here, go and read the DIY first before making false assumptions on some statements i posted below.

you can use a hand vacuum pump attached to bleeder valve and pull old fluid out instead of running back and forth to driver seat and kicking the brake pedal to push the fluid out.

[73sport]

** DUDE; replace your MASTER CYLINDER BEFORE YOU DIE! **

For what ever reason the cups in the master cylinder that are supposed to capture fluid and force it into the slave cylinders let fluid PAST them and their sealing ability has been compromised!

Usually this kind of thing happens AFTER an old M/C which was working fine is manually bled. By working fine I mean the brake pedal has never seen the floor board, but during bleeding operations it is pushed to the floor whereby it scrapes up a bunch of crap at the end of the MC that hasn't been moved in years cuz the pedal works and never goes that low (THE BOTTOM)! Make sense?

Then you bleed them and crap gets stuck under the rubber pistons and/or cuts the lip you have a failure. That crap puts tiny cuts and groves in the piston which allow fluid past the seal and failure is the result!

** The master cylinder has safety feature>> The FRONT AND REAR systems in hopes that BOTH PISTONS don't fail at once. YOURS DID!!!

The safety system to keep you alive failed! Did it trigger a brake light warning lamp? Prolly not because the light is normally only triggered when it detects an imbalance. i.e. front pressure <not equal> back pressure which triggers brake system light.

Bleed the system with the OLD M/C and get it running clean fluid. Install new MC and bleed system again! This keep the crap out of the new MC!


EDIT:

Sometimes you only get "one second chance" don't waste it!

[73sport]

Originally Posted by fenixus

. . . . .instead of running back and forth to driver seat and kicking the brake pedal to push the fluid out.

i can't imagine getting all the air out using a one man bleed method as the pedal must remain at the floor when you crack the bleeder and then continue moving if it has travel to actually expell the fluid W/Out risk of letting air back into the system!

Have someone help if you choose this path. Your brakes will have way less bubbles. . .

-> They push, they tell you its down.
- you crack it, it bleeds.
-> They keep constant pressure and depress if it allows them too.
- you shut it, and tell them they can let up now.
- you instruct them to press again and hold it until you tighten the bleeder and tell them to let up.

[fenixus]

Originally Posted by 73sport

i can't imagine getting all the air out using a one man bleed method as the pedal must remain at the floor when you crack the bleeder and then continue moving if it has travel to actually expell the fluid W/Out risk of letting air back into the system!

hey not really that hard. you apply vacuum (e.g. 20-30inHg) BEFORE you open the bleeder screw then while still pumping up with one hand you open the bleeder screw with second hand and keep quickly pumping until pressure falls e.g. below 10inHg, then you close it before it reaches 0. where is the risk ? i've done it multiple times on all 4 corners and now have nice and hard brake pedal and brakes that can stop the car on dime

of course if you have a helper then go this way (i don't), will be faster way I guess.

[dave255]

Thanks for the replies everyone. 73sport, there was no brake warning light when this incident occurred. And I think you might be onto something because I bled the brake system for the first time in many years about 1-2 months ago(I should've mentioned this in original post) . I thought all was well though because after bleeding I had a firm solid brake pedal and could stop on a dime.

So you think when I bled the system I kicked up some crap from the back of the MC? Anyone else have any thoughts on this? Thanks again.

[71Corolla]

Originally Posted by dave255

Anyone else have any thoughts on this?

Yes.

** DUDE; replace your MASTER CYLINDER BEFORE YOU DIE! **

It might not be your master cylinder, but it sure sounds like it. To be safe, just replace it and go from there. It will give you the opportunity to replace/bleed the system as well.

[BamZipPow]

+1 on the master cylinder. Seen too many of them do the same thing. Do not drive that car until you git it fixed. It's not worth the bent metal or lives you would be putting at risk.

[dave255]

Ok, I'll replace the MC asap. Thanks everyone.

[73sport]

Quote:
Originally Posted by 73sport
i can't imagine getting all the air out using a one man bleed method as the pedal must remain at the floor when you crack the bleeder and then continue moving if it has travel to actually expell the fluid W/Out risk of letting air back into the system!

Originally Posted by fenixus

hey not really that hard. you apply vacuum (e.g. 20-30inHg) BEFORE you open the bleeder screw then while still pumping up with one hand you open the bleeder screw with second hand and keep quickly pumping until pressure falls e.g. below 10inHg, then you close it before it reaches 0. where is the risk ? i've done it multiple times on all 4 corners and now have nice and hard brake pedal and brakes that can stop the car on dime

of course if you have a helper then go this way (i don't), will be faster way I guess.

ALL - in this conversation it is Mixing TWO different methods of DYI bleeding.
1) = Manual with someone pumping the brakes & someone else releasing the pressure at the bleeder.
2) = Vacuum from a hand held pump, pulling fluid from the resovoir.

Try not to let it confuse you. #1 takes two people. #2 can be done solo.

[73sport]

ALL, this quote is being taken "out of context"

Originally Posted by fenixus

*
. . . instead of running back and forth to driver seat and kicking the brake pedal to push the fluid out.
*

OK - here's the truth - people read and see what they want to see and could interpret this as something they should do! My fear is someone will see this and think they can press the brake pedal down, run to bleeder, crack it loose, and then run back to the drivers seat and do it again and it will work. THIS WON'T Work!

Nothing personal, OK! Just don't want someone to make a costly mistake. Obviously most of us will push on the pedal before we drive away. . . but if the internet said you could do it it must be true..... {me being sacastic}

[fenixus]

yeah it is out of context (VERY!). it should be read together with the "DIY: brake flush" ONLY which i linked above. i hope everybody reading this has checked the link ... if not go and do it now, otherwise this sentence makes no sense and could possibly cause a fatal accident!

73sport, good you noticed it and imagined how it could be understood. my bad wording, i should have stated it related purely to the DIY I linked above.