need help / advice .. brakes failed on HIGHWAY

[miib14]

hi i was driving on the motorway down to bury (15 miles away),
what happened was as i pressed the pedal and it literally dropped to the flooor.. this was at about 70-80mph...
however took my foot off the pedal and pressed it again and it started to brake but still low, so did that afew times and it was ok....

drove for afew more miles and the same thing happened, pedal dropped to the floor... did what i did before and it was ok...

this carried on till i got to bury with alot of down gearing..


anyways went straight to the scrappy and he said that its most lykly Brake master cylinder or brake servo or low fluid or air leak...
there was enough fluid..
started the car up again and the brakes are fine no probs at all...

took it to a mechanic and he bled all the brakes..

they have been fine since then but im still worried about the brakes going again!!



anyway of checking if Brake master cylinder or brake servo is knackered?


also anyway of reducing brake pedal travel?

[BoyYota]

I would put my money on the brake master cylinder going bad. They always tend to start showing signs of 'sticking' or whatever they do and eventually you can barely brake at all. Put that brake master cylinder replacement at the top of your list.

[miib14]

is there anyway of checking its going?

[Kiwi-Corolla]

Originally Posted by miib14

is there anyway of checking its going?

A quick test is to drive forward a few feet, then press and hold the brake pedal. If while holding firm pressure on the brake pedal you feel the pedal, very slowly, falling downward toward the floor then replace the master cylinder ASAP. The only other way to check it that I know of would be to inspect for any fluid loss. Was the fluid level up to the 'FULL' mark? If it was lower than this mark then chances are that you have a small leak. A small leak can allow air to enter the hydraulic system, which results in the brakes feeling spongy, or not working at all, like you experienced. If a seal is worn inside the master cylinder then you can buy a rebuild kit, but it would be cheaper and easier just to replace it with one from a junkyard.

As for the servo, there's a quick test you can do on that too. With the engine off, press the brake pedal to make sure that the pedal doesn't go further than it's meant to. Now press the pedal again and start the engine (while still pressing the pedal). If the pedal goes down slightly then operation is normal.

You can check the brake pedal height by measuring from the upper face of the pedal rubber to the sound insulation sheet on the firewall nearest the floor. It should be between 135-145 millimetres on RHD models.

[miib14]

Originally Posted by Kiwi-Corolla

A quick test is to drive forward a few feet, then press and hold the brake pedal. If while holding firm pressure on the brake pedal you feel the pedal, very slowly, falling downward toward the floor then replace the master cylinder ASAP. The only other way to check it that I know of would be to inspect for any fluid loss. Was the fluid level up to the 'FULL' mark? If it was lower than this mark then chances are that you have a small leak. A small leak can allow air to enter the hydraulic system, which results in the brakes feeling spongy, or not working at all, like you experienced. If a seal is worn inside the master cylinder then you can buy a rebuild kit, but it would be cheaper and easier just to replace it with one from a junkyard.

there was no fluid loss.. the floor doesnt drop to the floor either
however when i pump the brakes really hard whilst engines on, the pedal right at its lowest bit makes a weird sound, like a spongy sound?

Originally Posted by Kiwi-Corolla

As for the servo, there's a quick test you can do on that too. With the engine off, press the brake pedal to make sure that the pedal doesn't go further than it's meant to. Now press the pedal again and start the engine (while still pressing the pedal). If the pedal goes down slightly then operation is normal.

so pump the brakes until it goes hard when engine is off, then start engine?
did this and pedal when slowly down to where it should go down to (when you brake and pedal is pressed)..

Originally Posted by Kiwi-Corolla

You can check the brake pedal height by measuring from the upper face of the pedal rubber to the sound insulation sheet on the firewall nearest the floor. It should be between 135-145 millimetres on RHD models.

i want the brakes to engage quicker thats why i want travel distance shortened.

[Kiwi-Corolla]

Originally Posted by miib14

there was no fluid loss.. the floor doesnt drop to the floor either
however when i pump the brakes really hard whilst engines on, the pedal right at its lowest bit makes a weird sound, like a spongy sound?

That could possibly be related to a fault with the brake master cylinder.

Originally Posted by miib14

so pump the brakes until it goes hard when engine is off, then start engine?
did this and pedal when slowly down to where it should go down to (when you brake and pedal is pressed)..

Yep, pump it once or twice then take your foot off it. Then press the brake pedal and start the engine while the pedal is still pressed. If it dropped slightly (further than it does when braking) then that's good.

Originally Posted by miib14

i want the brakes to engage quicker thats why i want travel distance shortened.

Ok cool. There's a locknut on the rear of the pedal arm that you can undo which allows you to adjust the pushrod. It's easiest to remove the lower part of the dash to get in there easily and to see what you're doing. Then you just have to unplug the connector for the brake light switch, loosen the locknut, remove the switch, loosen the locknut on the back of the pedal arm, and rotate the pushrod. Don't forget to tighten the pedal arm locknut afterwards. Press the brake pedal a few times to get any vacuum out of the system so you can see if it's at the right height. When you're done, reinstall the brake light switch until the plunger is fully depressed, but the brake pedal does not move, and tighten the locknut. Then reconnect the connector for the switch. Last but not least, check that your brake lights are functioning correctly when you press the pedal.

[speedy25]

This is DEFINITELY a master cylinder failure in process. The only way to test it is to crash your car. (NOT recommended!) Your mechanic who bled the brakes should have known this and fixed it properly. That reaction to the problem is the stuff that lawsuits are made of.

Repair it pronto!

-SP

[BoyYota]

Originally Posted by speedy25

This is DEFINITELY a master cylinder failure in process. The only way to test it is to crash your car. (NOT recommended!) Your mechanic who bled the brakes should have known this and fixed it properly. That reaction to the problem is the stuff that lawsuits are made of.

Repair it pronto!

-SP

That's what I was thinking. Brake systems don't just throw a fluke at you. Something is going bad and that something is the brake cylinder.

[Bitter]

sounds like a bad master cylinder, just replace it....why chance it? cost of your car, medical bills, insurance, life, etc vs the master cylinder?

[miib14]

ok no problem guys...
will definetly get it changed..

[miib14]

how hard is it to change the master cylinder?

[Kiwi-Corolla]

Originally Posted by miib14

how hard is it to change the master cylinder?

It's a relatively easy job to do. Just make sure you don't get any brake fluid on the paintwork. It would pay to put a protective cover over the side of the fender to prevent any drips etc. Here's some instructions from my Gregory's repair manual:

1. Remove the master cylinder reservoir cap and, using a syringe, withdraw the brake fluid from the reservoir into a container.

2. Disconnect the wiring connector from the brake fluid level warning switch located on the side of the master cylinder reservoir.

3. Disconnect the brake pipes from the master cylinder. Plug the pipes to prevent entry of dirt.

4. Remove the nuts retaining the master cylinder to the brake booster. Remove the plate retaining the booster check valve and carefully push the bracket retaining the pipe junction connector, away from the master cylinder.

5. Remove the master cylinder from the vehicle. If damaged, remove the gasket from the brake booster.

Installation is a reversal of the removal process, with attention to the following points:

1. Secure the master cylinder in a vice equipped with soft jaws and pour a small amount of clean brake fluid into the reservoir. Pump the master cylinder piston with a blunt rod or Phillips screwdriver until fluid begins to emerge from the outlets. If necessary, block the primary and secondary outlets alternately until a clear stream of fluid is expelled at all outlets.

2. If necessary, install a new gasket to the brake booster and loosely install the master cylinder. Place the pipe junction bracket and place the check valve retaining plate over the booster stud. Connect the brake pipes to the master cylinder outlets. Do not fully tighten the pipes at this stage.

3. Tighten the master cylinder retaining nuts securely.

4. Securely tighten the brake pipes and connect the brake fluid warning switch wiring connector.

5. Fill the master reservoir with clean brake fluid and bleed the brakes.

[miib14]

took it to my local mechanic...
the nut in the middle of the wheel hub was very loose...



he said that it could be because of this that the brake pedal dropped to the floor..

could this have happened?

[Bitter]

uh if that nut was very loose I hope he also replaced the wheel bearing.

it *could*, but why was that nut loose? its torqued to like 130 lb/ft and then staked into place with a chisel or held by a cotter key.

[miib14]

the little pin was missing....
the bearing didnt need replacing, did it?