brake lever travel

[Dave20046]

Originally Posted by svtomo

have you dropped the bike?

Not for a while.

[ophic]

Originally Posted by Dave20046

I'm having the same issue. I've overhauled everything but the calipers yet the problem persists. The braking's useable and safe but it bugs me.

I've got brand new braided lines, a new mastercylinder, new fluid and new pads. It's either air trapped and being impossible to move or knackered calipers. Though there are no signs to lead me to think there's a leak.

Thanks Dave. I might start by overhauling my calipers then. We'll meet somewhere in the middle

As I commute on it, I get precious little time to undertake major overhauls. I strongly suspect that the overhaul kits available for master cylinder or calipers, don't include the brake line banjo bolt seals. Can anyone confirm this? It's not the sort of thing I need to find out at 7pm on a saturday with my brakes in bits, nowhere open on sunday and therefore no way to get to work on monday.

[Bibio]

halfords do copper washers

[Dave20046]

My calipers have been serviced but not replaced (that's what I meant by overhaul) Everything else is new or working second hand.

grr

Change your caliper seals. What's happening is that due to their age they are distorting a lot when you apply the brakes then when you release they spring back and retract the pistons too far with them. They are designed to do this slightly to give the pads clearance on the discs but only minimally.

As a temporary measure or to test the theory take the pads out and unbolt the calipers one at a time. Work the pistons out (not till they drop) then push them back in. Do this a few times on each piston and it will reset the grab the seals have on the pistons. You should then find that your lost movement at the lever is much reduced.

Voila! Point proved - change the seals. Happened on both my K3 1000's

[SVGrandad]

Originally Posted by Rocket

Change your caliper seals. What's happening is that due to their age they are distorting a lot when you apply the brakes then when you release they spring back and retract the pistons too far with them. They are designed to do this slightly to give the pads clearance on the discs but only minimally.

As a temporary measure or to test the theory take the pads out and unbolt the calipers one at a time. Work the pistons out (not till they drop) then push them back in. Do this a few times on each piston and it will reset the grab the seals have on the pistons. You should then find that your lost movement at the lever is much reduced.

Voila! Point proved - change the seals. Happened on both my K3 1000's

Rocket - if your theory is correct, shouldn't you be able to "pump up" the brakes as the seals would not return the pistons quicker than you could pump the lever? Ophic said his brakes did not pump up. Am happy to be proved wrong!
Cheers
SVGrandad

[Dave20046]

worth a pop though. I'll give it a shot today rocket.

[ophic]

Originally Posted by Rocket

Change your caliper seals. What's happening is that due to their age they are distorting a lot when you apply the brakes then when you release they spring back and retract the pistons too far with them. They are designed to do this slightly to give the pads clearance on the discs but only minimally.

As a temporary measure or to test the theory take the pads out and unbolt the calipers one at a time. Work the pistons out (not till they drop) then push them back in. Do this a few times on each piston and it will reset the grab the seals have on the pistons. You should then find that your lost movement at the lever is much reduced.

Voila! Point proved - change the seals. Happened on both my K3 1000's

Originally Posted by SVGrandad

Rocket - if your theory is correct, shouldn't you be able to "pump up" the brakes as the seals would not return the pistons quicker than you could pump the lever? Ophic said his brakes did not pump up. Am happy to be proved wrong!
Cheers
SVGrandad

Rocket, this fits the symptoms. I'll pull the calipers apart at some point. Thanks for the advice

SVGrandad, are you suggesting that the seals would return to position slower than the master cylinder? I'd say that the master cylinder has a lot more travel, and it has to move a long way before more fluid can get in. But i'll try pumping the lever very fast anyway.

I've always found that overhauling the front calipers makes the brakes feel much sharper and reduced the travel on the lever. I think it's because the white crap builds up in the seal grooves and forces the seals out to the point where they pinch between piston and bore.

If the calipers have not been regularly maintained they'll probably need new seals.


Cheers Keith

[yorkie_chris]

Strip them and clean them. If the seals have nipped onto the pistons it's only a slight bit more wear of the pads away from the dust seals popping out and making the brakes drag.

Rubber grease the seals and pistons.