Brake system nightmare

[serenitycamper]

Quick overview: Journey to Bala, both front brakes stuck on. Replaced both front calipers, bleed screws, pads, seals, fluid flushed and replaced etc.

Journey to local shop, both brakes stuck on. Replaced flexi pipes.

Journey to parents house, 20 mins tops, both brakes stuck on AGAIN.

Is it the master cylinder seals?

Rears are fine but the fronts just do the same thing over and over again. Really at the end of my tether now.

Pleeeeeeease help

[Aidan]

are they the sliding caliper type ? are they free to slide easily or are the pins worn, damaged, bent ?
IF when stuck on you pop the bleed nipple are they under hydraulic pressure ?

[serenitycamper]

Sliders are fine, I copper greased them when I replaced all the seals. They slide perfectly.
When I say stuck on, what I mean is they release, but not far enough so they're always stuck to the disc and consequently wherever I go the front wheels are untouchably hot. Not good.

If I release the bleed screw immediately after the brake is released it sprays out. So I guess yes is the answer!

[JamesKT25]

This is the exact problem im having at the moment!

[tobydog]

Did you change the hoses?

When they're old they break down inside and act like a one way valve, when you push the brake pedal down you force the fluid into the cylinder but there is too much of a restriction to allow the fluid back out of the caliper.

[serenitycamper]

'Replaced flexi pipes.'

Yup!!! Ok let's clear this up...

NEW ITEMS..calipers, pistons, piston seals (both), slider seals, flexi hoses, bleed screws, fluid (completely bled through 1.5 litres).

So what's left that can cause this as this is my everyday bus and it's now really p@@@g me off!

[California Dreamin]

We had this exact same fault with Gavin's Bay Window at Berlin Fest....on investigation it turned out that his brake pedal 'return sping' had snapped and the pedal wasn't fully returning to its stop.

So to explain what was happening:....the the 'ports' in the master cylinder were not fully open to the reservoir...therefore, the fluid was heating up in the brake line, expanding and so partially applying the front brakes (the expanded fluid would normally return to the reservoir via these open ports)
I guess this could also happen if the link from the brake pedal didn't have enough free play..either way, not allowing the ports to 'vent' to the reservoir with the pedal released.

This normally doesn't effect the rear drums as there is a lot more clearance between shoes and drums.
Front pad 'clearance' is achieved by the caliper seal 'deforming' during brake application (the rubber lip twisting slightly) and then 're-forming' to shape when the pedal is release to pull back the pistons ever so slightly.....All clever stuff.

Martin

Martin

[tobydog]

Diagnosing brake pulls and brake lock up:

http://www.agcoauto.com/content/news/p2_articleid/202" onclick="window.open(this.href);return false;

?

[serenitycamper]

Before the bus was taken off the road for restoration there was NOTHING wrong with the brake system as I drove it every day. Since it being stood for 2 years with no brake use, all these issues have arisen so I don't know how the pedal travel can have altered?

I'll read the post and see what u can learn from that.

Basically would failing master cylinder seals cause this problem?

[California Dreamin]

Well one this is for sure...the master cylinder is causing this......whether it's a fault internally with the tandem seals or externally with rod length/pedal adjustment/pedal not returning.....the master cylinder is not allowing the excess fluid to return to the reservoir.

Martin

[itchyfeet]

This is the exact problem im having at the moment!

I thought you said yours just stopped happening? implying it is was just sticking

[JamesKT25]

Im not covinced it has . If i leave it long enough it doesnt do it again until i brake hard or for extended periods. I just cant decide. Havent had the chance to take it on any more proper drives to work it out...

[serenitycamper]

So is there a separate return spring on the pedal?

[California Dreamin]

Perhaps you need to have a look...... at the same time you can check for the required clearance on the push rod.

Martin

[serenitycamper]

Right well i've just driven it around the block and when the brake pedal is released there is no extra travel if I attempt to hook my foot under the pedal and pull it higher, so I'm guessing all is ok in that area.

Am I wrong? Is there more to it?