K11 OSF seizing brake

[toob]

Hi,
Occasionally (say every third journey) the OS front brake binds to the point that smoke comes from the wheel and it drives similar to the hand brake being applied. After leaving to cool down for 20 minutes, the problem goes away for the rest of the journey (even if this is hundreds of miles).
I’ve changed the complete calliper with one from a breakers yard and yet the problem is still there. If the problem is going to happen it always does within the first 10 miles otherwise it’s okay for the rest of the day. What else could be causing the problem? Logic says that there is only one other component being the master cylinder/brake servo unit. However I would have thought that any problem there would effect all brakes not just the OSF. Is there a equalizing valve in the front circuit that could cause this?
Any clues as to what to check / change next would be great.
K11 1998 1.0 manual

Thanks
Mark

 

[getawaycar]

Assuming you have made sure the pads move freely in the calliper carrier and that the piston can be pumped out/shoved back relatively easy I'd be looking at the flexi pipe.
The hose can perish and partially block on the inside to the point it holds the pressure on. I've found this on early neglected K11s.

 

[toob]

Thanks.. that would fit the scenario where when the pipe is cold fluid doesn't flow back but after fluid has heated due to partial seizing the hose expands.

When you say, "pads move freely in the calliper carrier" the pads do not seem to move freely as they are held firm by the stainless pad clips. I thought the required movement comes from the sprung carrier moving against the calliper base. These two calliper parts seem sprung loaded although there's no springs inside just metal rods. These move freely. Is that what you mean or should the pads move within the stainless clips?

Also would fitting a used pipe be OK or should I be looking at getting a new flexi pipe?

 

[frank]

the spring clips should only stop them rattling mark, and you should be able to slide the pads about with light force.
and the randomness is probably heat related imo

 

[organdonor]

Personally I would take the callipers off and blow the pistons out using an air line and grease them all up and replace the seals. (Y)

 

[pollyp]

the spring clips should only be tight enough against the pads to stop em freely rattling about as frank said, cleaned/lightly wirebrushed free from baked muck so its shiny n smooth, and lightly smeared with copper grease. if they hung onto the pads too tight then the increased friction makes em bind slightly and requires more force and time to clear away from the disc surface.

the sliding guide pins should slide in/out smoothly with no resistance and no springiness.
lack of grease or ingress of dirt or rust inside the pins creates resistance so the caliper can't move back once braking is released.
too much grease in the pins seals the pin against the carrier bore making it into a piston trapping and squeezing the air inside. this springiness constantly pushes the caliper to one side.
in both cases this means the caliper is always pushing the outer pad against the disc which gives the symptoms of binding brakes, hotter than usual brake temps, uneven wear between inner & outer pads, poor economy, steering to one side.

 

[pollyp]

Personally I would take the callipers off and blow the pistons out using an air line and grease them all up and replace the seals. (Y)

my LH pulsar caliper piston was also sticking recently. i just moved the piston in/out afew times to lube the piston seal and all is fine