XT brake fettling

I've had horrendous squealing from my front brakes & some rotor rub front & back. My LBS suggested that it may be seized pistons – sure enough when I removed the pads & squeezed the brake levers only one piston moved front and rear. I have got the stiff pistons moving by holding the mobile one in & pumping the lever to get them out & then putting a little teflon lube on them. A drop of fluid came out of the front brake at the caliper (I couldn't see where from), nothing at the rear. When I replaced the pads & wheels the front brake worked fine, the rear didn't bite.
1. Is the loss of the fluid from the front likely to be significant?
2. How can I 'de-sponge' the rear? I have no spare brake fluid & am planning to ride tomorrow.

Thanks

Anyone?

on the front i wouldn't be worried about one drop of fluid, especially if it works fine now, but if more leaks out you'll need to replace the seals.

As for the rear, you're looking at a rebleed, get yourself down to halfords or your lbs if it's open today and get some fluid.

Also, i wouldn't lube the pistons with teflon, don't know that it would do any harm but i use brake fluid so no probs with potential contamination or seal damage

maybe just try riding the bike for a few minutes, whilst braking alot… i have found xt brakes seem to take a little while sometimes to start working properly, once they have been fiddled with…

hopefully the back will then start to work a bit better.

Thanks, I'll get some fluid for lubing/bleeding.

There's not a lot of fluid in bicycle brakes. I'd guess between 20 and 50ml depending on the system. Without seeing, it's hard to tell but what you saw from the front caliper could just be the teflon lube you were using. The best way to check for a leak is to clean and dry the system and then use an old toe strap to pull the brake on hard overnight. If there's a leak, you should see a drip on the bottom of the caliper in the morning. (lean the bike over so that if it does leak, it doesn't do so on the tyre).

As for the sponginess, that sounds like it needs bleeding. A possible temp. help would be to tei the lever off in the hope that the pressure in the system will force any air to rise and then escape into the reservoir.

The rear brake not biting could be that the system doesn't "pump" up. If you'vre got a particularly sticky piston, perhaps it's not coming out of the caliper at all now you've pushed it back. Are the pads contacting the rotor when you pull the lever? Is the lever firming up when you pull it or is there nothing there? Is there a chance you've contaminated the pads?

By the way, the squealing could have been an alignment issue.

Went for a ride anyway…………….Mysteriously the rear lever firmed up and all was ok (apart from my mate who ripped his tyre wall). Next DIY service will be my Maverick speedball, so expect numpty questions on that soon.

I'm guessing you fettled the pistons with the bike upside down, if there's any air in the reservoir it can get pulled into the system doing this,causing the soft lever. If you're lucky it'll find it's way back into the reservoir as yours seem to have done, may be worth topping up/removing the air to prevent it happening again.