My frotn brakes have gone spongy..

Since I bpushed the piston back into the R/H caliper. I bled them for about 2 hours and still no different. Could it be the lines? Or is it more likely to be the master cylinder? It gets better when I've ridden for about 5 miles, and when cold it will "Pump up" which makes me think it's the cylinder. It's not leaking anywhere.

[fizzwheel]

Not sure.

However when I zip tied my brake lever to the handle bar over night brakes were less spongey in the morning.

Might be worth giving that a try ?

Yeah, done that a few times and it does help, but seems to go back how it is now while standing at work, but is fine for the ride in. Cheers

[embee]

http://www.mandp.co.uk/productInfo.aspx?catRef=533338



(mityvac not draper!)

It's been bled through mate, but cheers anyway.

Sounds like sticky piston seals and/or warped disks.

When the seals get sticky, they hold the pistons "in" the caliper, meaning more lever travel to get them (well the pad) to contact the disk. Clamping the lever overnight cures this temporarily as it pushes the pistons where they should be, but the seals will pull the pistons back in eventually if they are sticking, giving you the squishy lever again for the same reasons.

Alternatively could be warped disks. As the disk rotates and the warped part moves past the pad, it knocks the piston back into the caliper, giving you the same problems.

Or finally could be really knackered rubber lines if you still have the o.e ones.

Very unlikely for it to be the master cylinder from the symtoms you are describing.

Hope this helps mate.

Dan.

Check the caliper can move properly on its pins. Watch the calipers/disks when you squeeze the brake lever. If you see lateral movement, you may have a problem. Too much grease on the pins can cause a hydraulic lock so the caliper can't move properly and the floating disk moves instead!

Well, that's my take on it.

[TSM]

When you pushed the pistons back in, were they clean or all gunked up?

Make sure the bleed nipple is not too loose. I spent ages with bubbles coming out turns out the nipple was so loose it was letting air in. Only open it a tiny bit and see if that helps.

Hope that's all it is mate

Originally Posted by Dan_SV

Sounds like sticky piston seals and/or warped disks.

When the seals get sticky, they hold the pistons "in" the caliper, meaning more lever travel to get them (well the pad) to contact the disk. Clamping the lever overnight cures this temporarily as it pushes the pistons where they should be, but the seals will pull the pistons back in eventually if they are sticking, giving you the squishy lever again for the same reasons.

Alternatively could be warped disks. As the disk rotates and the warped part moves past the pad, it knocks the piston back into the caliper, giving you the same problems.

Or finally could be really knackered rubber lines if you still have the o.e ones.

Very unlikely for it to be the master cylinder from the symtoms you are describing.

Hope this helps mate.

Dan.

Cheers for your help, much appreciated, the sticky seals does seem the most likely thing as they are the thigns affected by pushign the pistons back in. Looks like ANOTHER overhaul for my brakes I do have the O.E lines, but I best replace the seals before I fork out for braided lines methinks.