brakes fail while driving

[BOSXR8]

i was driving back from the airport the other day, car is running fine, i come to slow down and the brake pedal goes down all the way verry slowly and the car slows down real slow, instead of stoping dead in its tracks, luckily there was no car infront of me. i pull over see the master cylinder, fluid is fine so i jump back in ,the brake warning light lights up, so does the abs light and the traction cotnrol light, i put it into drive and drive foward, and nothing. no brakes, foot just goes down all the way to the firewall.

so i turn it off, turn it back on a few montues later and everything is fine. i manage to drive home just around the corner, the brakes would work one second then the next the warning light would come and the brakes would go.

im thinking its the brake booster, anyone had similiar problems?

i booked it in with the mechanic and im not driving it untill it gets fixed. its so dissapointing that a car with only 100 000kms on the clock can have problems like this. to be honest i actually enjoy driving my ef gli with 500 000kms on the clock instead of the au ghia. very dissapointed.

[Lukeyson]

yeah while reading that i thinking brake booster is on the fritz !

[howesy]

gotta disagree with you about the booster. Your brake pedal has a physical link to the master cylinder through the booster. the booster simply creates a negative pressure on the master cylinder side in order to reduce the effort required to effectively brake the vehicle. Even if the booster had a hole in the diaphram and was R.S. your brake pedal should still not sink to the floor as the physical connection to the master cylinder would mean that it couldn't. your choices are that you either have a cracked or split line somewhere or a caliper piston seal or wheel cylinder seal is R.S. or maybe rear master seal.
These options would have the fluid level going down and if it is not then the seal inside the master cylinder is R.S which may allow fluid to pass in between the front and rear chambers which causes your pedal to sink. Start by looking for brake fluid.

[GK]

Originally Posted by howesy

Start by looking for brake fluid.

Agreed, that is the easier and most logical place to start the diagnostic run. Start with the easier, and I guess cheaper options first.

Must have given you a scare. Thankfully you weren't on the freeway emergency braking or similar.

All the best with it.

GK

[Eu-GenixX]

yeah.. definately not brake booster...

[macca13]

Just a thought but it could be the abs playing up as it modulates brake pressure, could also explain the traction control light as it uses the same sensors as the abs.

[botch]

your brake warning light only comes on when there is low fluid in the reservoir.
all ABS systems revert to standard (non-abs) braking when the abs fails.

it may have an airlock in the system or your bads are very badly worn and all the fluid is going into moving the piston on the caliper when you brake, causing the fliud to drop .

[ratter]

Some correct and incorrect info here.

It is not your booster. If your booster failed you would have a very hard pedal and still have full braking ability, but just a lot harder pedal.
The Brake warning light can come on when 1 piston in the master cylider travels further than the other piston, normally caused by leaking seals in the master or a external fluid leak from the brake hoses or calipers.
Take your wheels off first and check for fluid leaks around bleed nipples or hose fittings. Check for fluid leaks near brake pads which caused be caused by leaking piston seals (not very common)
Check for hoses and pipes for leaks.
Check ABS unit for leaks
If no external leaks are present, it's more likely that your master cylinder has failed.

[superroo]

Originally Posted by botch

your brake warning light only comes on when there is low fluid in the reservoir.

Sorry, but wrong. The brake warning light works off pressure in the braking system. Cause when you bleed the brakes, all is fine untill you open a nipple, pedel goeas to the floor and the brake warning light comes on. This happened to me, and the resivour was full.

As everyone is saying, it more sound like you've got a leak in the system somewhere. My suggestion, put the car up on jacks, take the wheels off, pump the pedel about a dozen time, then look at the lines, bleeders, pads, to see if there's any fluid about. If theres no fluid, then the problem is in the master cylinder.

Cheers

[botch]

sorry but were all wrong - you must have fluid to have something to pressureize !!

[nitroman]

There is a sensor on the master cylinder that can leak sometimes. Disconnect the wire connection and see if it is leaking.

[BOSXR8]

thankyou all for your comments guys much appreciated, i work 7 days a week (even this time of year yes!) and have no time to even check it out, my mechanic is going to have a look at it tomorrow, the front discs are badly worn but the brakes all around are new (previous owner changed brakes but discs are hammered- dumbass). i have noticed though when i put my foot on the brake and take it off there is a clunk sound comming from the back, (the uni needs changing too so i thought it was from that) although i could be mistaken now and it might be from the rear brakes....

hmmm ill see what the mechanic says tomorrow.

this is the 2nd time i have ever had brake fail while driving, first time was in my eb and i went over the kerb onto grass, thankfully both times have been close calls only, lets hope there is not a third.

thanks again guys ill update you all with what the problem is tomorrow.

cheers.

[GK]

If the discs are worn too thin, the pistons can push out too far. That's why they have a recommended minimum thickness.

I wonder if this would result in the symptoms you have experienced?

GK