Running a Shimano 2012 slx rear brake with a 160mm G3 rotor on the rear – and I just can’t seem to get the thing to lock up. Not that I really need it to, but as hard as I squeeze the lever the wheel never locks. On the front I’m running a 180mm rotor and that thing will stop very quickly.

I’ve replaced the pads for Superstars organic pads, and have bled both brakes. Is it just because I’m running the 160mm rotor?

Sticky piston?

Don’t think so, there’s just no real ‘bite’ just a bit of drawn out slow stopping…

Does the lever feel firm or does it pull back to the bar? Might be contamination on the rotor/pads (carried over to new pads on the rotor) if firm, or air in the system if it is soft.
The latter is why I have just sent off for a bleed kit for my Elixirs, so I had better be right!

Oops

Feels firm, you can tell when the pads are contacting the rotor – but like I said, they just don’t seem to bite.

I cleaned the rotors with isopropoyl when I installed the new pads.

Try bleeding them !!,if you changed the pads & cleaned the discs,then theres not a lot else you can do..other than try a warranty claim,it may be faulty,who knows.. 😉

Have they had any bedding in time after fitting the new pads or is this the first run up the road?

Has it ever felt sharp?

Make sure they’re clean and free from dirt when braking. Organic pads are terrible when wet, dirty etc. also check the brake for any leaks or signs of pad-brake fluid contamination.

Cleaning with isopropyl alcohol is a wise move before fitting new pads but the slightest contact with brake fluid and you can usually write off any set of pads.

Sounds like there is still air in them to me. Get that bleed kit out again.

don’t you have to “cook” your pads after fitting new ones? whack new pads on, from a fair speed, slam them on to a full stop a few times, should be cooked nicely

A quick way I check ‘in the field’ to see if pads are glazed or contaminated is to rub some sandy mud onto the rotor – if braking is dramatically restored its the pads – else it air in the system.

‘But’ on a new set of brake – I’d be tempted to LBS / send ’em back.

Edit- Oh and what spchantler said too first.