I've been running 2 bikes with hydraulic discs for 5 years without a glitch until yesterday.

My brake lever is pulling all the way back to the bar and is only slowing the wheel rather than stopping it. The rotor is clean and the pads are not worn.

I guess that I've lost pressure.

Is it a big job to fix?

What brakes? I have just done my Magura Julie HPs after changing the hoses on them.
It was quite easy to do with the kit and I have never bled a brake before. So if a ham fisted idiot like me can do it anyone can 🙂

Shimano somethingorothers… M515?

They should be quite pain free with a bleed kit as they are mineral oil so no nasty dot fluid to kill stuff.

One of these I guess http://www.chainreactioncycles.com/Models.aspx?ModelID=663

and then this http://www.parktool.com/repair/readhowto.asp?id=126

Hope this helps 🙂

Ta.

However, with limited free time and many years of trouble free running i'm tempted to use one of these.

adds post to reduce the spiders kill rate whilst gently mocking him for not fettling and then scurries away.

😀

I get about 2 hours a week to do my own thing at the moment. I don't want to spend it dirtying my tool kit.

get all the prep stuff and bleedkit etc should you need one and allow yourself some time to do them properly.

Time? See above.

I 've had xtr's trouble free for 4-5yrs until last years summer Polaris when I lost all pressure in the back, no signs of a leak, so I thought it must be air. Took off the reservoir cap to find that the brake fluid was well below the correct level. Topped it up and squeezed the lever gently a few times with the cap still off, that allowed all the air out and the brake was back to perfect. It's happened once since, with the same cure, so I think that there's probably a slight leak (but so tiny that there's no obvious evidence) The point being that each time has only taken 5 minutes to cure (even if it needs doing every six months) And ten minutes a year isn't too much is it?

Tip, rotate your lever/reservoir so that it's horizontal before you take the cap off.

…and this morning it works again.

Brant and Shaun's tip was to fill the reservoir, open the drain nipple on the caliper (with a plastic tube attached) and cable tie the lever against the bars for as long as possible. Shaun said to put some business cards between the pads and pistons but that probably depends what business you're in.

Haunted, definitely.
Bet they make an unholy screaching noise as well.

Shimano receommend a sacrificial lamb, but the official one costs a fortune.
I tend to use a doner kebab – works just as well, cheaper and not quite as messy.

It's a very useful skill to have, sooner or later your bike or your mate's bike will go wrong just before a ride and that's not the ideal way to learn! There's nothing difficult about it at all, but it can be intimidating. It sounds like a faff but then so is dragging your bike to your LBS for what could be a 10 minute job.

I'll see how it goes. I wasn't going to take to the LBS and say "Take a look at this… It works!" as they would think I was a bit odd.

Just phoned the LBS. They'll do it for £15 which is only £3 more than buying the gear and doing it myself.

For most Shimano (all? not sure) all you really need is a wee bit of hose. But the ebay syring kits that cost about £3 make things much easier. S

and this morning it works again.

sounds like air in the lever assembly reservoir

This is my understanding…
If you've air in the lever assy then the brake will work until you work that air bubble into the hose.. then… brake will be spongy as described. Once you stop using the brakes, that bubble will likely migrate back into the highest point.. the lever assy and the brakes will work again until the cycles happens again.
The braking response depends only on the integrity of the fluid in the hose between the master lever piston and the caliper piston/s..so as long as you have no air in this section, all will be fine. as soon as you introduce air here, you get the effect you're describing.

so, you need to bleed. time spent here is probably better than time in the clinic 😉

/2p

Ta. That would make sense.

I had problems with my xt and slx brakes. I bled them the way I know from motorbikes and cars and couldn't get them to work, took it to LBS and got it back top notch…until I put the bike back in the shed…I tipped the bike onto its back wheel with the brake on and it the lever just went straight back. So

Got bleeding kit
filled pipe and syringe with oil,
took caliper off so i could get nipple at the right angle,
levelled reservoir and took cap off then
pushed fluid from the caliper UP to the reservoir.
Sorted brakes are really sharp now, recommend the reverse bleed