Shimano Disk Brake Problem - sticky cylinders

[womblechops]

I think if I can master my way around the minutiae of Shimano Alfine hydraulic braking systems I should be able to turn my hands to the resolution of the Middle East problems and the cure for all known diseases. However, the brakes are holding me up for now and so your kind input would be appreciated in order for me to get on to 'The Palestinian Question'.

I have suffered with squeaky rotors (in varying conditions) for years, and even the LBS has given up and refused to replace pads and bits because they were't worn, instead advising hard braking, degreasing, etc. You name it, I've tried it.

In fact I've tried it all so long without success I finally decided the pads probably were worn enough to merit replacement and so set aside this weekend to do a pad change and air bleed as all was also a bit spongy. All just about within my competency.

However: step 1 - on removal it appears that the pads are not the same shape as the ones in the Shimano parts diagram. Annoying, but solvable. I'll just put the old pads back in for now and pop down the bike shop and swap....

Step 2: I can't get the cylinders to retract enough to put the pads in then still get the rotor between them! I can't get them in with a spacer at all. So I released the pressure at the top of the system and noticed that there was no oil in the reservoir anyway. I pumped the lever to see if any rose from the bottom and 'pop' a cylinder appears now to have unseated itself and what little oil there was in the tubes (2-3 tsp) is now on my patio.

Fine, I think, I'll just recommission the system with fresh oil. But neither of the two cylinders will retract and one is standing very proud.

Do I have to undo the whole caliper to fix it? Any ideas?

 

[Scoosh]

OOOOPS !

2 things I have learned about hydraulic disc brakes:

1. DON'T turn the bike upside-down
2. DON'T touch the brake lever when the disc pads are not in place

As this is about the limit of my knowledge , I can but empathise with your predicament and offer a , a , even a .... but practical advice, I regret, is not available from this respondent.
I do, however, have total confidence in the collective CC wisdom to give you all the answer you need !

 

[J1780]

Coming from someone who rides road bikes only and doesn't actually own a mtb with hydraulic brakes although I am in the process of buying one this is what I'd do. I tinker a bit with my motorcycle and the following is how to do the same job on a motorbike.

Unbolt calipers, remove pads, pop cylinders carefully and slowly....be careful brake fluid or in some mtb systems mineral oil will leak out onto your patio (as the op discovered) so have bucket or something handy, next unbolt and split calipers, take out the pistons and seals carefully don't pinch the seals and give all including caliper inside and out a nice clean. Refit everything as it was and you SHOULD be good. In any case or if you are unsure the Lbs should be able to sort you out if you get into trouble. Good luck and easy does it.

Ohh yes I need to edit because I forgot to say you will obviously have to fill and bleed the system afterwards.

 

[lpretro1]

The concern I would have on splitting the caliper is that the o-ring between the transfer port may not work when you put them back together and as Shimano don't spares like this for their brakes, unlike other manufacturer's, you could end up with a bigger problem than you started with!

 

[womblechops]

Thanks all. Yes, the bike was firmly upright in its workstand. Yes, as soon as I touched the lever I knew I was doing wrong.

I think it will have to come apart as the whole thing is simply seized at the moment and as the pistons are almost touching it isn't as if I can get anything in there to prise them apart. Will update (once I have thoroughly wrecked it and put in a new caliper).

 

[Cubist]

As far as I know the Shimano calipers are not serviceable by mortals. You cannot get spares for them, inasmuch as you only have the choice of lever and reservoir assembly, hose, or calipers.
However, they are modular up to a point, with the possible exception of hose fittings at the calipers end, so you could source ANY Shimano hydraulic caliper and use it to replace your popped one.

In the meantime you have one chance left to repair this one, and I personally would advise against splitting the caliper. You're going to need to be careful, removing the reservoir cap to start so there's no pressure in the system, and then carefully use a knife blade to lever the pistons back in. Danger here is damaging the surface of the piston, but as the caliper may be destined for the bin anyway........

Make sure it's clean using IPA and a toothbrush or paintbrush and then use the flat of a blade with a wiggling action to push the piston back in. If you are lucky enough to get it back in, then get the old pads back in with card or a piece of ply in between so you can't repeat your error.

I don't want to sou d patronising, but did you try to refill the system from the top or the bottom?

Either way, use a syringe with the correct mineral oil to force fluid into the caliper via the bleed nipple. Keep the reservoir higher and horizontal as you do, and watch for fluid as it fills the hose, reservoir and then starts to overflow. Close the bleed nipple and replace the reservoir seal and cap. Now give everything a good clean with IPA and once there's no more ambient mineral oil to contaminate everything put the new pads in. Don't touch the lever......

Clean the rotor with IPA and a clean rag and put the wheel in. Slacken the calipe mounting bolts with a 5mm key, so that the caliper can float in its bolt slots, and now line up the pads with the rotor by eye. There should be the same gap between each side of the rotor. Make sure the gap is the same side to side and fore and aft. Nip up the bolts to finger tight and squeeze the lever, watching the pads as they are pushed towards the rotor. They should move smoothly and simultaneously, and should both contact the rotor at the same time. If they do, keep the lever squeezed and nip up the 5mm bolts a quarter turn at a time. Check for rub, whispering or run out by spinning the wheel, but be aware new pads will take a couple of rides to bed in.

Yu managed to make them sound very complicated, but they aren't really...... However, if you bugger about with them it's easy to get it wrong!

 

[womblechops]

Thanks. I shall do this. Although I might substitute IPA for a cheaper bottled bitter...

 

[Mile195]

I've never had a bike with hydraulic brakes, but I have changed plenty of pads on cars and motorcycles, as well as replacing the piston seals. The above description sounds good, but if you can, use a piece of wood to force the pistons back in if you can. I've also used a screwdriver with a bit of breakfast cereal packet folded in half over the tip in the past. Basically anything to stop metal touching metal.

 

[J1780]

In the meantime you have one chance left to repair this one, and I personally would advise against splitting the caliper. You're going to need to be careful, removing the reservoir cap to start so there's no pressure in the system, and then carefully use a knife blade to lever the pistons back in. Danger here is damaging the surface of the piston, but as the caliper may be destined for the bin anyway........

Make sure it's clean using IPA and a toothbrush or paintbrush and then use the flat of a blade with a wiggling action to push the piston back in. If you are lucky enough to get it back in, then get the old pads back in with card or a piece of ply in between so you can't repeat your error.

I'm not sure how the more or less standard service/pad replacement will help here. If the op pumped the lever and oil ended up all over the patio the seal in the port has been unseated. In order get it back in he has to A) be incredibly lucky with the above or B) split the caliper. Either way if shimano don't do spares op's getting a new caliper anyway.
Whatever you do don't use metal on metal as Mile195 has pointed out.

 

[Born2die]

I had this happen the other day mini me gave the brakes a handful whilst the wheel was off the bike. I have clarkes skeletal though I managed with a big screwdriver to pop the piston back in only problem was it went in at a funny angle lots of swearing later and some brute force I managed to get it back in ok bled the system and all is good.

 

[Cubist]

I'm not sure how the more or less standard service/pad replacement will help here. If the op pumped the lever and oil ended up all over the patio the seal in the port has been unseated. In order get it back in he has to A) be incredibly lucky with the above or B) split the caliper. Either way if shimano don't do spares op's getting a new caliper anyway.
Whatever you do don't use metal on metal as Mile195 has pointed out.

The OP describes that there is very little gap between the pads. There is no chance of his getting a plastic brake wedge or anything else between the piston faces to prise them apart, hence the suggestion of doing it carefully with a knife blade, fully in the knowledge that he MAY damage the ceramic piston face, but, as I've stressed, the caliper is likely to be bound for the bin in any case. I would not normally advocate using metal on the bare piston faces under normal circumstances.

Splitting the caliper.... sceptical. Given that the OP appears to be enthusiastic but not mechanically adept, then I would shie away from suggestions to split the caliper. But, as it's likely to be bound for the bin anyway......