The newer ones.

replaced pads and topped up the reservoir which has sorted the rear a treat but not the front. Could pull the lever to the bar without getting any force – pumped it a million times and taped it to the bar for a few hours which sorted it right out, topped up the reservoir again while spending about five minutes pumping the lever. an hour later it was as bad as before but there’s not space for more oil so I don’t think it can be air in the system.

I’ve ordered a full bleed kit and will replace the fluid but I wonder if anyone has had this before? If it’s water in the system (is that possible?) that would surely sink down to the callipers – is it therefore necessary to bleed it the wrong way (drain the system from the callipers and flush through from the lever)?

Buy the official shimano bleed kit. Works a treat.

went for epic… that much difference?

It might be the case that a seal has gone. With one of mine it was the lever reservoir seal just as they’d gone out of warranty. I actually managed to bodge a fix using super glue and they’ve been holding up great for the past 8 months.

Almost certainly just needs a proper bleed. Just because the reservoir is full doesn’t mean that there’s not air trapped in the hose or caliper somewhere. Very unlikely to be water in the system, but even if there is, it wouldn’t give these symptoms – water is an incompressible liquid, just like brake fluid.

Epic bleed kit works well. It’s only a 10 minute job once you’ve done it once. Strongly advise taking out the pads and using a spacer; also good to have all the tools on a bench in front of you. You’ll need a 7mm ring spanner as well.

You obviously have no idea. Take it to your LBS. Water in the system, how did that get there. It’s a closed system, with a bleed point at each end.

And it’s mineral oil so not hygroscopic!!!!!!!

I bled an SLX one backwards with a syringe on the caliper and the shimano pot on the reservoir. Worked out OK for me to back bleed as going the other way didn’t work.

Google is your friend. Bleed from the calliper up. Then if you still have a problem do a lever bubble bleed. Simples

The shimano kit has a convenient funnel for the reservoir so no messing around with duel syringes. Bleed up and down as shimano instructions, but sometimes just attaching the funnel, fitting a bleed block, filling funnel with oil and squeezing the lever to expel air is enough

Why do you need to fit a bleed block to do a bubble bleed?

See here for a bubble bleed ➡

http://m.pinkbike.com/news/tech-spotlight-5-minute-bubble-bleed-2014.html

Downhilldave you win the friendly poster award, thanks for your helpful advice. The system should indeed be closed but that doesn’t mean it is impervious to breach. It would be unusual but then so are the symptoms – usually tapping the hose while working the lever will bring any air bubbles up to the reservoir, if there has been fluid loss it can then be topped up. If water had *somehow* got into the system it would sit below the oil, being denser, and so flushing from the bottom might not remove it all, hence speculation that bleeding top down might be more effective. Water, while not as compressible as air, is not incompressible. I hope I haven’t damaged your self confidence too badly – keep trolling, practise makes perfect xx

Mineral oil is slightly more compressible than water…

Cool, didn’t know that. Every day is a school day! 🙂

Ah, I get it. Shimano in their wisdom make a brake system that is not sealed and let’s mineral oil mitigate past the said seals and water enter the system. Cool. Shimano is the easiest system to bleed IMHO. Not trolling but trying to assist and have considerable experience in automotive, motorcycle, and bicycle brake systems. Happy trails 😉