Blimey, no brakes

[John]

I spent the morning changing my front brake pads, and while I was at it changed the fluid for some fresh stuff. All well and good except now the pedal just sinks to the carpet. I flushed the best part of two litres of fluid through the system now, and no sign of any air coming out, and no leaks I can see. Fluid level isn't dropping, just the pedal... it seems like the seals in the master cylinder have given out, but it's something of a coincidence the pedal was fine before I started. Perhaps the seals just couldn't cope with the clean fluid? I'm now weighing up the pros and cons of a seal kit and a load of time and effort against a new master cylinder, or could it be something else entirely?

[Andrew S]

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Hi John

Its air. I would get a helper at the front wheel bleed nipple ready to open and then just before you open it, I would try and pump the brake and whilst foot is on the way down, release the nipple and quickly take your foot off pedal. It should suck the fluid down and start pushing the air out.

There is another way I believe and that isto push the pedal down and then put a heavy object like a brick on it and leave it overnight andthe air will come to the top. Haven't tried this and it may just be applicable tobleeding the clutch

Andrew

[RogerP]

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Just a thought, did you pump the brake pedal after fitting the pads and before you bleed the system? cause you need to push the pistons back out !!by pumping the pedal a few times.

You mention coincidence did you bleed the brakes by pumping the pedal or use something like an easy bleed, by pumping the pedal you move the pistons a seals past there normal travel this can cause the seals to tear, but it seems strange to show so quick.

I am assuming you have checked the shuttle valve.

Roger Phillips

[John]

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I bled it with an easy-bleed thingy and the missus pushing the peddle. As I say, I've bled the best part of two litres of fluid through and not a hint of a bubble either at the wheels or gurgling up at the reservoir. The brakes don't feel spongey, the peddle just slowly sinks to the floor, rather as though I'm still bleeding them. It sinks faster if the engine is running.

What do you mean by "shuttle valve" - where is this?

[GDPR]

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The master cyl seals are shot - any master over 10 years old when it goes to the end of it's travel (which it doesn't usually unless you have a leak) damages the seals as that section of the master hasn't seen a piston or seal since it was built - there is often a tiny amount of corrosion in the lower part of the bore, or a wear ridge that cattles the seal hence loss of pressure at the top of the stroke.

Always bleed with a pressure or vacuum bleeder and don't touch the pedal during the bleed process, unless you have a new or freshly reconned master cyl.... then this won't happen.

Russ:dude:victim of many a master cyl failure from this problem.

[John]

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Bugger. What do you recon - seal kit and a bunch of grief fitting it only to find the cylinder is worn anyway, or straight for a new master cylinder? I'm tempted to go for the latter. I can see no reason to go mad on a BMW kit though.

[RogerP]

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John wrote:

I bled it with an easy-bleed thingy and the missus pushing the peddle. As I say, I've bled the best part of two litres of fluid through and not a hint of a bubble either at the wheels or gurgling up at the reservoir. The brakes don't feel spongey, the peddle just slowly sinks to the floor, rather as though I'm still bleeding them.

What do you mean by "shuttle valve" - where is this?

John

The shuttle valve is located on the N/S inner wing, it's were all the brake pipes connect and the purpose is if you get a leak either front or back the valve moves and stops the fluid being pushed to that part, and just leaving the good part for braking, and I can't remember whether it's a diagonal split or front and rear. So lets say it's front and rear and you get a leak onthe rear it stops fluid being pumped to the rear and you only get braking to the front.

The brakes don't feel spongey, the peddle just slowly sinks to the floor, rather as though I'm still bleeding them.

That does sound a bit like the master cylinder. Maybe somebody else can give some clues.

Roger Phillips

[John]

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I thought that was just a warning device. I didn't think it was actually a valve.

[Kevin Garrod]

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John

You have a more extreme version of my problem, I still have brakes although the rears are poor.

I would recommend a new M/C even if you don't go for the BMW version like me.

I had the same problem on my wife's MG, I bought a recon kit, but was unable to disemble the old M/C so ended up replacing it. Brakes are too important to skimp on!

[stustag]

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Hi John

I tried to replace the seals not a good idea buy a new one from Paddocks (cheapest and Genuine Part) and fit and forget I did and alls been fine since.

Stuart

[John]

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I've asked for a price from these people...

http://www.powertrackbrakes.co.uk

I'll see what they come up with, otherwise Paddocks will be getting an order in the next day or two...

[jamcarr2]

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John wrote:

I thought that was just a warning device. I didn't think it was actually a valve.

Yes it is just a warning device and not a very good one ,mine is constantly on and the brakes are fine just had new master cylinder , pads , rear shoes .copper pipes and braided flexie hose so I know they are working also just passed its mot light always on so I have disconnected the wire .

john

[mad cyclist]

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John wrote:

I've asked for a price from these people...

http://www.powertrackbrakes.co.uk

I'll see what they come up with, otherwise Paddocks will be getting an order in the next day or two...

Mr A Hart does a buy it now on ebay for brand new genuine parts, think mine was £135, only one i could find at the time, know he can be a little dear on ocassions bit you know the part from hart wont fall apart!

reconning one is a nightmare!

[DJT]

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jamcarr2 wrote:

John wrote:

I thought that was just a warning device. I didn't think it was actually a valve.

Yes it is just a warning device and not a very good one ,mine is constantly on and the brakes are fine just had new master cylinder , pads , rear shoes .copper pipes and braided flexie hose so I know they are working also just passed its mot light always on so I have disconnected the wire .

john

If the valve is working properly and travelling the full distance, it will shut off supply. Proved this myself last week when bleeding the brakes.

Dave

[John]

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...the part from hart wont fall apart!

I'm a poet, I know it...:P