I bought a second had trek ex 6 the other month and found the brakes, shimano br m575, were awful, so I swapped the hope mono minis off my hard tail and thought nothing of it.
Myself and the misses were planning a gentle sustrans ride tomorrow, so thought i’d dust off the hard tail and finally sort the brakes. I have just bleed them and checked the pads, a little air and pads seem pretty new.
They are still not stopping well, or even locking up the back wheel!
Has anyone got any ideas what could be wrong or how the proble could be sorted?
Thanks all, Christof

fluid present / contaminated pads / rotors?
sticking pistons
wrong spacing on set up, thus pistons not working well

You sure they are bled properly?

Check both pistons are moving.

As above: rotors/pads contaminated or not bled. How does the lever feel when trying to lock up?

Some of those cheaper shimano brakes have a flaw where when you pull hard on the lever, the 2 piece calliper pushes apart slightly allowing a small amount of fluid to leak onto the disk/pads, contaminating them and giving you piss poor stopping power. Usually you will slow down gradually and come to a stop with a harsh judderey squealing sound.

Either bin them or expect to clean them regularly

Sebgt- Yes, harsh squeal and judder!

Matt out and about- the levers feel good, firm, but not too firm. The pads and rotas seem clean, but gave them a wipe over. (I thought mineral oil was suppose to be fairly ok on pads and rotas, unlike trad dot fluid?)

Junkyard and I am roughrider- I think I’ve bleed them right, I followed the YouTube video? And it seems both pistons are moving?

I’ve got some of the very low end deores. I found my pads didn’t want to bed in at all, squealed and didn’t stop me despite a number of hard braking efforts.

Found a different than usual way to bed them in – and have brilliant power now.

However the front bedded in eventually just by braking normally on a hill, although it still wasn’t as good as the rear ( which it’d used the new method on) This method worked for me and they are now both brilliant.

Find a hill. Drag brake for say 20 seconds or so and then do a few on and off’s maybe at the bottom.
Push back up hill, dragging brake.
Descent again and keep braking on and off hard.

Then just use your judgement as weather to drag a bit more ( i had to do it for about 4 runs up and down ) or just pump the lever.

So in essence, drag the brake a fair amount at first ( to get really hot), pump the level lots, drag brake a bit more.

The other thing i did was to use some fine sandpaper beforehand on the rotors and clean the rotors up with cleaner( as i’d used these with other brakes)

The idea is the get the pads and rotor hot, and then apply sharp braking. After about 10 runs of a hill mine bed in brillianty and the squealing stopped completely (although it was present though the bedding in process)

I’d expect aftermarket pads to bed in much easier.

For the deores I’d try cleaning the pads and rotors with some sandpaper. Soaking the pads in meths for 30 minutes, ( if contamination is suspected ) and then ( carefully !!) setting them alight somewhere safe ie on concrete – making sure you do not have any meths etc on your hands ). Then clean rotors with cleaner / meths. Rebed pads in as described above.

Check the calipers beforehand for any signs of fluid. If you suspect they maybe leaking as mentioned above I’d be tempted as a last ditch attempt to clean them up and apply something like silicon sealant to the joins, maybe braking hard a few times before the sealant has fully set.

I’d only do the second part if their was evidence of leaking though and you were considering binning them.

Also you could try adding a bit of brake fluid on the piston shafts and moving them in and out a bit as they could be dry if not used for a while.

May be worth trying new pads too.

Thanks everyone! I’ll give a clean and try bedding is as suggested.
Here’s hoping I don’t need to buy new ones! 😉

If the lever doesn’t feel right or feels spongey, or pulls back to the bars then there’s air in the system. Might be worth ( with the brakes assembled . attached as normal ) opening the covers at the brake levers , tie wrapping or using a lace or something to keep the levers pulled in, and tapping the hoses. Leqve the levers like this for some time. Then retop up at the lever if required. Some air bubbles may rise throught the system. You can also carefully tap the caliper a bit with the handle of a screwdriver. ( providing you do not spill the fuild )

Woah, back up there a little.

The pads and rotas seem clean, but gave them a wipe over. (I thought mineral oil was suppose to be fairly ok on pads and rotas, unlike trad dot fluid?)

Am I reading this right, you cleaned the pads and disks with oil? All that advice about bleeding and bedding in up there ^ Useless now. Clean disks with strong solvent. Replace pads. Then do the bedding in thing if you feel it’s necessary.

oops.. new pads, clean rotors with proper cleaner or meths then sandpaper / then more meths/ cleaner and clean calipers. Clean both sides of the rotor.

It’s still worth opening up the top covers if and tapping hoses etc anyway. Just bed in as normal, sharp braking with a little speed.

Woah, back up there a little.

The pads and rotas seem clean, but gave them a wipe over. (I thought mineral oil was suppose to be fairly ok on pads and rotas, unlike trad dot fluid?)
Am I reading this right, you cleaned the pads and disks with oil?

Have you bled DOT brakes with mineral oil-that is how I am reading that?

Either way how did you bleed them with the pads in?

Surely you remove and push pistons back and do a full flush etc

Have you bled DOT brakes with mineral oil-that is how I am reading that?

Shimano brakes all use mineral oil .

I bought a second had trek ex 6 the other month and found the brakes, shimano br m575, were awful, so I swapped the hope mono minis off my hard tail and thought nothing of it.

He bled some Hopes surley??

A bit difficult to be sure but I read it as he took the Hopes off the hardtail and put them on the Fuel , then he tried the hardtail , which presumably by then had the Shimanos on it and they were awful .

Perhaps the OP could give us a definitive answer .
Either way putting mineral oil on your brakes and discs is not going to make them work very well and would appear to be the cause of the problem here .

Hmm, I read it as he was saying that mineral oil doesn’t fubar your discs/pads as much as DOT, but that he gave the discs a clean anyway (I’m assuming with disc cleaner or something, but I seem to be the optimist here)

and yeah, he swapped the hardtail brakes off for these shonky ones, & he is trying to get the hardtail with new shonkness working properly

Waits for OP to come back & see how sidetracked by semantics everyone has gotten

re reading I think he has bled shimano ones and I got it wrong

Yes, I have bleed my hopes using dot.
Yes, I bleed my shimano with mineral oil
No, I haven’t soaked or cleaned the pads and rotas in said oil.
🙄

just to add..

also try unbolting the caliper ( on deores )and tapping this as well as moving it to around at various different angles at the same time.

Assuming the callipers are moving and the levers don’t feel awful spongy, its usually pad and rotor contamination. Even trace oil from your skin can affect brake performance. It usually happens to me if I over oil the chain and some flicks off onto the frame and sometimes the rotor. You can try and purge the pads by burning off the contamination with a clean flame. Scrub rotors with spirit and a spotless scourer and cloth.