Urgent Brake Help!!!!!!!!!!!!!!!!!!!

[Sancho]

A leak will occur with or without engine running......

Where????

[NiftyNev]

so it must be a problem with the internal seals, surely????

That's my opinion. I hope I'm right. I can't see it being anything else. Try more pressure on the brake pedal with engine off. It may just leak past the seals with the extra help from the servo. Either way something is not right.

Nev

[Apache]

Have to agree with Nev. If the engine is off, its simply much harder fo force the fluid past the internal seals in a leaky master cylinder. This could give the impression that the pedal is rock hard. As soon as the servo is working, there's huge amplification of pedal force and it becomes 'easy' to force fluid past the seals so the pedal goes to the floor.

This happens in Australia too - though the fluid travels in the opposite direction due to the coriolis effect.

[Sancho]

This happens in Australia too - though the fluid travels in the opposite direction due to the coriolis effect.

The coriolis effect has minimal influence, although it should be born in mind that a servo in Australia is a petrol station, so braking systems have to be substantially larger.

[meooo]

Where????

Oooooh! anywhere











even in the antipedes

[That Ruddy Squirrel]

[watching this thread for IOTY 2009 candidates]

[Sancho]

Oooooh! anywhere



even in the antipedes

But if the fluid level isn't dropping it can't be leaking can it? Unless it's somehow getting replaced by something else? Air?

[MattF]

But if the fluid level isn't dropping it can't be leaking can it? Unless it's somehow getting replaced by something else? Air?

There may still be air in there, which will compress, whereas the hydraulic fluid won't.

[Sancho]

There may still be air in there, which will compress, whereas the hydraulic fluid won't.

True, but it's been bled a fair few times.

[meooo]

A pressure bleeder may help dispel any lingering air, also making sure the m/cyl doesn't empty during bleeding.
Maybe clamp off the other brakes as you bleed one corner, forcing fluid your way and nowhere else.

[MattF]

True, but it's been bled a fair few times.

True, but that doesn't imply it has been done correctly or completely. I'd agree with Albannach on this one. The circumstances under which the problem arose, coupled with a replacement cylinder exhibiting the same symptoms point to air in the system. It *may* be the master cylinder at fault, but air is the logical conclusion, all facts considered.

[Sancho]

This thread seems to have taken a turn towards being a genuine exchange of views in the hope of finding a solution to a problem.

How odd.

If it turns out you're right, I reserve the right to point at my last bracketed comment of post #43

[meooo]

Could equally be an "anti-squeal" backing on the pads making the pedal feel soft.....until the pistons get a good grip into it it can act as a spring...If the pads have it of course, some do, others don't.

Or the pads not free fitting in the calipers and sticking, causing the pistons to be pushed back, also high spots on discs can cause this effect, next time you use the brakes the pedal hits the floor and you have to pump the pistons back out.

[MattF]

If it turns out you're right, I reserve the right to point at my last bracketed comment of post #43

Nice. The 'cover my arse from all angles' approach.

Meooo, I have a spanky spade here, perfect for those deeper holes, if you wish to borrow it?

[NiftyNev]

True, but that doesn't imply it has been done correctly or completely. I'd agree with Albannach on this one. The circumstances under which the problem arose, coupled with a replacement cylinder exhibiting the same symptoms point to air in the system. It *may* be the master cylinder at fault, but air is the logical conclusion, all facts considered.

Bleed the master cylinder and then the brakes again. Bleed the master at the brake line connections. If that fails to solve the problem then it must be the master cylinder which is faulty.

Nev