I have Shimano BR-M315 hydraulic brakes on my Cube, but the braking power feels very low.

I tried adding some oil, letting the air out, changing brake pads, cleaning the discs... Everything I could think of, but it still feels week. Actually none of the steps improved anything.

 

How week the brakes actually are. I can push the bike forward slightly when holding the brake with full power.

I really have to try hard, but I can get the wheel to spin a little.

Or for example, when coming to a full stop, I can not brake hard enough to come even close to lifting the rear wheel.

 

Are my expectations too high, or should the wheel be 100% blocked when braking fully?

 

Are my expectations too high, or should the wheel be 100% blocked when braking fully?

 

Something is wrong. They should be locked firm when brakes are applied.

 

Do the levers come all the way to the bars when you pull them?

No. I used the middle screw to move them further away. They are mildly stiff for the first 2cm of travel, and than very stiff for the rest.

I spent too much time trying to fix a front brake with this same problem. In the end I swapped it out for this inexpensive deal that someone recommended on this forum. Sorted.

 

http://www.jejamescycles.com/tektro-draco-1-hydraulic-disc-brake.html?gclid=Cj0KEQjwx6TJBRCWtsiXpI7bhOYBEiQA1en3F6ZUnqXzXgxNMn9AQqkzvnKKZ3KiSCXx0XfcwNkz5ZQaAqCd8P8HAQ

Something must be wrong if the brake won't lock the wheel when you're stationary. If you give under-rated brakes a hard time when riding, they can overheat and get all sorts of other problems.

 

Does the brake bind a little if you try and spin the wheel without applying the brake?

 

Try loosening the two caliper screws (radial direction ones), then hold the brake on while you re-tighten them.

Brakes probably did overheat a few times, but they work the same from day 1.

Without applying the brakes, the wheel spins freely. there is a small gap between the pads and the disc.

 

Just to clarify. The wheel does lock when brakes are applied. But the brakes let go a bit, if I push the bike hard.

If the calliper pistons extend and retract correctly then have a look at your disc surface, if it has been over heated the surface may have a blue/grey hue.

Discs have definitely changed color! Will add pictures later.

Just to clarify. The wheel does lock when brakes are applied. But the brakes let go a bit, if I push the bike hard.

That's the bit that shows something is wrong. If you haven;t already done so, take the caliper off, remove the pads and clean all round the pistons with a toothbrush. Try some new pads. Maybe your spoilt them when you cooked them. If you cooked your brake more than once, think about sintered pads, a bigger disc or a better brake.

I changed the pads from original Shimano to cheap Chinese... no difference.

I have worn the originals down to zero in 300 miles.

Perhaps I will really get new/better/bigger brakes for the next season.

This is how my disc looks.

Hasn't been warm then, mine are all blue around the 'spokes'

did not last one ride with my 4 piston calipers as was cheap rotor from china.

Today I had a chat with a young lad who has just started a pedelec taxi business here in town. He has one of those delta trike things weighing 130 kg powered by the Japanese mid motor (sun something?).

 

Guess what brake he has on the front wheel? Magura hydraulic rim brake and he can't say enough nice things about it! Of course the rims all round are ultra strong DH rims.

I have just fitted a new pr of M315's to a non assisted bike I've just built and I have M355's on my Bosch powered Cube, both bikes stop on a sixpence and quite capable of locking the wheels.

Sound to me like you have oil, grease or soap on your discs & pads ( it dose happen, a friends father once oiled his sons discs whilst we were on holiday, explaining they looked a little rusty, that was on a gold wing )

 

Re-reading the OP if everything is fully degreased and there's no air in the system then I'd be looking at the hoses for crimps and creases or any damage. Back in my motorbike days, inefficient brakes were often cured with new hoses.

Shimano to cheap Chinese... no difference.

 

I'd bin the cheap Chinese pads and buy OE Shimano pads again.

Good to read up on stuff. We have a few problems with brakes, Hubs is probably going to try sintered pads, if that don't work then better brakes are on the cards.

Thanks guys.

I had a first ride after fixing/cleaning yesterday. After descending for a while the brakes started squealing (I hope that's the right word) (making a LOT of high pitched noise). Also I could smell them, but did not dare to touch them.

 

After cooling down, now I would say they work a bit better, but they started to lock/unlock/lock/unlock when braking hard. Right before I stop.

 

I will buy original pads today and see if that makes any difference.

Hubs had just bought some better brakes, Zee's and I've got some sintered pads. His haven't come as yet, but my new pads are fantastic, stop really well and my the squealing has stopped. May get some floating discs next. Got them from uberbike.

 

After cooling down, now I would say they work a bit better, but they started to lock/unlock/lock/unlock when braking hard. Right before I stop.

 

 

Are you sure the discs aren`t warped?

Spin the front wheel while looking down at the disc