Bleeding Brake Problem

[Ashman]

I have replaced the discs, pads and lines. Then replaced the bleed screws as one was rounded off. Yet when i bleed the system the pedal goes straight to the floor. I've gone through 2 bottles of AP Racing fluid and still nothing.

I'm thinking master cylinder, thoughts?

It's the last hurdle before mot time

[13Black]

Has the master got a bleed screw on it? If so definitely bleed that first and last to be sure.

[13Black]

How big is a bottle also? 1L should be enough for brakes and clutch if you don't waste much.

[Ashman]

500ml bottles, should be enough.

[Ashman]

Whereabouts would the bleed screw be? I've not seen it.

[warpc0il]

Only the early (pre-ignition 06) have a bleed screw on the master cylinder.

Try some ptfe tape on the caliper bleed screws, to stop air getting drawn in around the threads.

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[Ashman]

Could that be the problem even with new bleed screws?

[SeriousSam]

Which method were you using to bleed the brakes? If you're doing it alone, you might want to get someone to help you, the two person method is the most successful one I've ever used. Having replaced the lines you will have introduced a bunch of air into the system, and it can take a lot of fluid to bleed that air out. I seem to remember going through 1.5l when I did it. The master cylinder can hold a lot of air as well, so bleed that if you can.

[Ashman]

2 person, one pumping the brakes and the other at the calipers. I used a clear pipe and bottle with some fluid in the bottom to watch for air bubbles.

How would i bleed the master as there is no bleed screws that i can see?

[mrspiller]

I used a good 500 ml before we got any pedal after changing all like you , then a further 500 ml to get it right , done a few laps of the track and bled another 500 ml on at the track then another 500 ml when we got home to get them perfect . I found it best to bleed furthest away until you get a bit of peddle then work around about 4 times . Do all the nipples up tight and pump , if you got air going in you’ll surely have a leak of fluid at that point ?


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[Ashman]

You'd have thought so but i can't see any signs of a leak at all. I'll get some more fluid and give it another try a few times. The problem is that with my health the way it is it's taking it out of me to keep doing it over and over. I may end up paying someone to do it for me if i can't get the pedal to firm up. *Fingers crossed*

[13Black]

Sounds like you're doing the right things, maybe the level dropped below min slightly and it's got a bubble somewhere. Fluid is cheap, keep at it methinks.

[mrspiller]

You'd have thought so but i can't see any signs of a leak at all. I'll get some more fluid and give it another try a few times. The problem is that with my health the way it is it's taking it out of me to keep doing it over and over. I may end up paying someone to do it for me if i can't get the pedal to firm up. *Fingers crossed*

I had my son and mrs Pressing the brake pedal , one thing I was told ( not sure if it’s true ) that the pedal should go right down to the floor and there is a secondary push on the last few inches of the pedal until you get some fluid through , surly if all is new you could te use the fluid to start it off ?


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[13Black]

Eeeeee.

Never investigated further but its generally said that you're not meant to use the last 25%ish of the pedal - there can be debris in the generally unused last part of the master cylinder than may score the seal and cause internal leaks.

I never use full travel when bleeding brakes and get on fine.

That said, I think it's unlikely to cause problems, just possible, so best to avoid.

[mrspiller]

Eeeeee.

Never investigated further but its generally said that you're not meant to use the last 25%ish of the pedal - there can be debris in the generally unused last part of the master cylinder than may score the seal and cause internal leaks.

I never use full travel when bleeding brakes and get on fine.

That said, I think it's unlikely to cause problems, just possible, so best to avoid.

@ neil parry


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[ChrisHolmes]

Forgive me for asking the obvious but you are pressing the pedal first, then slackening the nipple and tightening it before releasing the pedal and pressing it again to repeat the process.

[Ashman]

Yes, pushing the pedal down and releasing the screw, pumping until bubbles disappear and then holding pedal down while tightening the screw. There are bubbles coming out every time and they always disappear so we assume it's done. Then we go round again and there's more bubbles. When starting the car the pedal softens and the revs also rise a little when pumping brakes so i assume the master cylinder is working ok.

[ChrisHolmes]

push pedal down, open nipple, close nipple, release pedal, repeat. pumping it with nipple open will introduce more air,

[ChrisHolmes]

Ha! Our posts crossed

That's not how I was taught to do it, the pumping bit just sucks air back in every time you release the pedal.

Press pedal and hold
Release nipple, the pedal will then go down to the floor
Tighten nipple
And keep repeating as above until the bubbles stop and the pedal does not go right to the floor unless the nipple is released.
Then on to the next one.

There is the possibility though that of you have allowed all the fluid to drain out then you may have air in the ABS unit and I am not sure if that can be bled out by normall bleeding.

[13Black]

Controversial melon:

When flushing the majority of the fluid through, I've always been fine leaving the nipple open and just pumping reservoirs of fluid though, to get the old stuff out.

Only the last bit when wanting to get the remaining air out do I have the nipple closed. Then on the pedal. Very quickly nipple open and closed. Repeat twice more usually.

[ChrisHolmes]

Rather than "pumping" try just pressing the pedal once, slowly, when the bled screw is opne just a crack and get the 2nd person to nip the screw up, just before you get to the bottom of the pedal movement.

This means that the fluid can only flow down.

It takes some coordination to keep repeating this;
- you put a light pressure on the pedal
- crack screw open slightly, until fluid flows and pedal moves
- nip screw before pedal bottoms
- repeat.

[warpc0il]

I've found the easiest method to initially fill the lines is suction on the nipple

A syringe, as sold to dose lambs, works well, though a modified breast pump works even better.

Just be ready to refill tank to avoid pulling air in.

[Ashman]

i wouldn't have thought it would suck air back in with the end of the pipe in the fluid in the bottle. It should just suck fluid back in.

[PeteH]

Sucks it past the threads of the bleed nipples. You won't be able to bleed properly if you release the pedal with the nipple open.

There. Lots of us agree on this, and do it the same way.....

[SeriousSam]

I've just remembered I wrote this up a while back, in my typically verbose fashion. Method works though

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