Hey guys

I've just dug the XT660R out after a few months of sitting unused. After cleaning and lubing the chain I headed off round the block to check the bike was OK, only to find that the front brakes are almost non-existent. Lever pressure at the bar seems normal but the bike just doesn't want to stop. The XT has always been rubbish on the brakes, and scares the hell out of me when I come back to it from a modern bike, but this is something else! It's never been capable of an emergency stop, but now it barely stops at all.

Maybe the pads are contaminated? Is there anything I should do to clean the disc, or the pads? Or rough them up? Or check caliper operation?

My money would be on the pistons being stuck in the caliper through lack or use/movement, or the slider pins are seized solid, specially if the lever still feels taught. The brake fluid may have picked up some moisture during the lay up too, so for the sake of a few quids worth of brake fluid, a flush and bleed would be a good plan after you've freed up the pistons/sliders.

If you think the brakes were a bit dodgy before, it's quite likely that the pistons and sliders were partly corroded already?

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Thanks.

Before you posted I had taken the pads out, given them a clean and a rub on some wet and dry paper, and then cleaned the caliper with brake cleaner. The pistons looked like new, although I don't have a brake pad spreader and I couldn't move the pistons by hand. Reassembling everything, there was definitely more feel in the brakes, although still not on the same scale as most other bikes I've ridden. After a 3 minute ride round the block with a bit of braking, the disc was almost too hot to touch. I don't know if this is normal, or whether it's indicative of the pistons not retracting properly and keeping light pressure on the disc. Maybe this is what glazes the pads?

Should I be able to move the pistons by hand without a screwdriver or pliers? How do I know if they're a bit sticky?

If the discs are too hot to touch after a short ride, then the pads are binding on the discs. This could be the pistons, but could equally be the caliper sliding pins being stuck as I mentioned earlier. It will also, as you say, end up glazing the pads.

You really need to take the caliper off and try and get some movement back into the sliding part of the caliper. You can try lubricating the sliding pins and working the two parts of the caliper back and forth, but you may need to strip it to clean everything up.

It is possible to move the pistons back by hand, but not all that easy. generally lever them back, but they shouldn't take excessive force. Check that the reservoir isn't full to the brim though because the fluid needs space to get back in there. If it's brimmed that pistons won't push back because they'll be nowhere for the fluid to go.

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At the risk of asking a really dumb question...

There's no spring or anything to actually move the pads away from the disc when the pistons retract slightly. Even if the pistons are moving smoothly, is it not possible for the pads to remain in light contact with the disc anyway??

Yes. There is no return spring as such, so the discs do very lightly touch the disc, but not so as you'd notice and certainly not enough to make the discs hot. This is why even the slightest amount of corrosion on the pistons or sliders will hinder the pads' return after the brakes have been applied. There is a certain amount of springiness in the disc (and as its floating) which will help return things back to an equilibrium. Other than that you are reliant on a lot of components sliding freely.

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