A bit frustrating – they were fine out of the box for 2 rides, all I did was turn the bike upside down, remove the rear wheel and reposition the caliper with the hose inside instead of outside the seat stay.

Now it take 30 seconds of enthusiastic pumping at the lever to get the feel back to normal – let it stand for 10 mins an the levers back to the ‘bar again.

Why has that happened and I assume I now have to bleed them?

Does sound like air got in there.

Assuming the new ones work a bit like the old ones, I’d just loosen your brake levers on the bars and make them as level as possible. Zip tie the levers back to the bar, leave it overnight, the air bubbles will gradually float up into the reservoir.

Open the top and put a drop of mineral oil in there in the morning. Should be sorted.

Cheers Toasty – done, I’ll check it out in the morning.

Disc brakes have been around for a long time now and really aren’t very complex. I’m perplexed as to why this is a continuous reoccurring theme on STW, when there already all the info you need here, just behind the search box.

What always confuses me, is that tying the levers back to the bar CLOSES off the system to the reservoir – I’m not saying it doesn’t work, but WHY does this work?

The system is only open (I.e. air can rise all the way up into the reservoir) with the lever open, not pulled to the bar!

DrP

The enforced pressure in the system forces the air to rise through the hose to the lever, where it stay until you release the lever then rises through the oil in the reservoir?

Just a guess.

Bubble compression. They travel easier in a smaller space when they’re smaller. Pressure doesn’t move them directly.

They all build up at the master cylinder and aggregate. Soon as you take open the lever they get more of a chance to travel into the reservoir.

Aye, but they don’t leave the reservoir unlike when you bleed the brake, so sooner or later they tend to get back into the working fluid. A very effective bodge but still a bodge.

OP- they had a slightly iffy bleed from new, with air left in the reservoir. A perfect bleed leaves no air anywhere in the system and prevents this from occurring but perfect isn’t always so easy to come by.

Northwind – ah – so when I turned the bike upside down air in the reservoir travelled back up the hose. So the original advice will work as it’ll force the air back in there, with air left in the reservoir though.

The only permanent fix is a full bleed.

Incidentally – anyone got a link a vid / instructions to bleed the M780 design – the one with the bleed screw on top of the cover……?

Due to lack of workshop I cut down my hoses and swapped them over in the shed the other day. The fluid left in the cuttings was dripped into the levers (where the hose was removed) and both hoses were connected back up. I expected to have to do a bit more but they are rock solid and unless I experience any problems I probably won’t be bleeding them properly just for the sake of bleeding.

Usual hassle free shimano hose trimming and calliper alignment in 10 mins. Pad clearance and quality rotors on shimano disc brakes are the best in the biz.

*rotors that run true without the need to go tweaking them. If only everyone else got it right like shimano.

Probably best to get one of the Shimano bleed pots(about £3 or £4)to purge the air, we do it on every bike that comes with them as nobody wants brake failure on their new bike (or old one, for that matter. Also costs us major money to collect and resend a bike.). It’s not just a case of topping up the reservoir, as you’ll see when using it, keep flicking the lever until bubbles stop coming up, then do it whilst tilting the lever at angles you wouldn’t be able to without the cup-you’ll be surprised how many more bubbles this will release, each one being another step closer to potential brake failure.

Unless I’m changing a hose or changing alll the oil, I generally just do the lever to the bars thing. It generally sorts them out in one shot and they don’t need touching for a year or so, when I do the same again.

Aye, but they don’t leave the reservoir unlike when you bleed the brake, so sooner or later they tend to get back into the working fluid. A very effective bodge but still a bodge.

As I said in my original post, if you open the reservoir up in the morning, put a couple of drops of mineral oil in to top them up, the air DOES leave the reservoir. If anything I’d say the opposite, even if I’d bled them via syringes that day, I’d do the bar trick overnight, as it leaves them feeling perfect.

The reservoirs just won’t have been topped up properly from new, turning the bike upside down let this air float into the system.

Toasty – its worked a treat, I’ve woken up to a nice solid lever (ooerr). Many thanks.

I haven’t the fluid to top up the reservoir today, but I’ll order some.

I’m still bemused though as to whether I need a special shimano syringe to fit the bleed screw for this and squeeze some fluid in, or only for a full bleed? Or for this, do I just remove the top cover and drip some in?

Edit: – Its actuall more solid that my front lever so now, so I’ll repeat for that overnight tonight.

I haven’t the fluid to top up the reservoir today, but I’ll order some

Yeah, fear not, worst case scenario the air gets back into the cable from the reservoir and you have to leave it over night again.

Can’t comment on the special bleed block thing, on the older ones you could just drop some mineral oil in the top. It’d be a huge shame if they’ve sacked this off, it was one of the big selling points for me.

As soon as you start using syringes and things you stand the chance of introducing new little bubbles and end up haveing to pass a brakes worth of oil through the system.

Toasty my lever went back to the bar mid ride, not suddenly so I didn’t die.

After some research I need the pot / syringe which I’ve ordered, but it’s a one way bleed so it’s easy to do – the pot goes on the lever to catch excess oil as you pump it using a tube / syringe from the caliper end.

Guess I need to do it properly.

Ah shame 🙁

Cheers for the info, even doing a full bleed with syringes on the old one just needed 2 bits of plastic tubing, 2 syringes and some mineral oil, all the bits cost about £10 on ebay and has kept 2 sets of brakes going for 4 years. Sounds like they’ve realised people aren’t feeding them!

Mid-ride does sound curious, too many backflips by the sound of it!