How to tell if it's the master cylinder...

[MarkyB]

Try gentle pressure on the brake pedal too, however you push it the pedal shouldn't sink.

[JaneHibbert]

couldnt resits. went out and pumped the brakes twice to get a hard brake and then kept my foot on it as if doing an emergency brake - it didn't move!

[IslipMinor]

Good news! Looks like the master cylinder is OK.

First thing to do now is to adjust all the brakes correctly and see if the pedal is good and solid, and will not 'pump up'. If it is than that is the end of the problem. If not then tighten the brake adjusters right up and go through the complete bleeding process again. After that the pedal should be rock solid, as there is no cylinder movement. If so adjust the brakes to the normal position and check the pedal again.

[JaneHibbert]

went out again and before pumping it went to the floor again...

I'll do more tests and do what ive been advised sunday morning. will report back then

[JaneHibbert]

okay so adjusted everything up tight, some pedal travel obviously up to where it engages and then quite tight. bled all brakes and this time i seem to have a firm pedal! no 100% happy - i might try bleeding again, but certainly it doesnt need pumping before being effective. thanks everybody!

[mike.perry]

Once all the air bubbles have been pumped out of the plastic tube there is no point in bleeding any more

[JaneHibbert]

God

when i left it last night it was, after a half inch movement, quite firm - it certainly didn't seem to be going down to the floor. i even took it for a drive and the brakes worked really really well. i went round then and could see no leaks and all fine.

sorted i thought, and said that on here.

now, this morning, i went out to the car and the pedal goes half way down again! one pump and it was hard again.

It must be a slowly leaking MC surely, allowing air in?

[sudburypaul]

Well, if you have bled the system numerous times, checked all joints and cylinders for leaks and found none than it does sound like the m/c is the obvious culprit. However, not to confuse the issue even more, I had similar symptoms with mine - pedal going well down at first then hard with pumping and quickly back to soft again, though fluid from what was a quite new m/c was not going down. I checked the cylinders for leaks and found a very slippery rear drum and shoes. I assumed it was the cylinder so changed it and put on new shoes, though could not see an obvious brake fluid leak, and it was okay for a short while. Then same symptoms again. Eventually I traced it down to a worn bearing seal in the rear axle that was leaking oil into the drum. When it was replaced and another new cylinder and shoes put on the symptoms disappeared. It was like the oil in the drum was mimicking a fluid leak or air lock. Just a thought but have you checked in the rear drums for any slippery substances in there?

Paul

[bmcecosse]

No! That indicates that the brakes are STILL not adjusted up correctly. And so - that first pump brings the shoes to contact the drums, then the little 'top hat' seal holds the shoes up there for a few hours - but they will leak off overnight.

[JaneHibbert]

So you are saying bmcecosse that I need to tighten up the shoes a little bit more? They are slightly rubbing at the moment, but admitedly only very slightly - they should be difficult to turn with ones hand to be correct then?

[bmcecosse]

Well - not quite 'difficult to turn' but slightly rubbing is ok. Are the rears adjusted correctly - handbrake cables loosened off, then the cams adjusted up till slight rubbing - then cables re-tightened ? Without being cheeky....... you do know there are two adjusters in each front wheel...?

[JaneHibbert]

yes, i do but can only deal with one at a time as there is only one hole. But I DID do those things, and the brakes were rubbing slightly and still soft until you pump. They were only rubbing slightly though... should I try and tighten them a bit more do you think?

[JaneHibbert]

And can see NO leak from anywhere...

[bmcecosse]

Yes - nip them up a bit. But you say after a single press the pedal is tight ? It's quite normal to have a long pedal first push after the car has been standing for a while - but it should stay tight while you are out and about in the car.

[JaneHibbert]

oh, one thing when i was putting the shoes back in the drivers side front the springs came off but dont 100% know if the springs went on properly, ie in the right holes - which holes should they be in?

[JaneHibbert]

when you say standing for a while - is just overnight a while?

[bmcecosse]

As long as the springs are ON - it's very difficult to put them in the wrong holes...... Standing for a while - I mean after an hour or so - is the pedal long again? Does it stay short if you go back to it after 20 minutes?

[JaneHibbert]

It stays short after 20 minutes or so yes, but after a couple of hours its long again

[MarkyB]

You need to check the chassis leg under the MC as well as the more obvious places.

A hard push on the brake pedal puts maximum pressure to force the seal against the cylinder wall, this can disguise seals that are marginal and will fail with a very gentle push.

When the pedal is pumped up how much free play is there on the pedal, there needs to be some but not too much.

[bmcecosse]

Sounds ok to me - adjust up the brakes if you can. Frankly I develop a habit of checking the pedal before I NEED the brakes - just to check the pedal is right up there. It's not all that often on a normal road that you don't use the brakes for more than 20 minutes......