soft hydraulic brake

steven_191 · Nearly there... Joined: 31 May 2009 Karma :

I have some old shimano deore LX brakes. The combined brake and gear lever type.

They had always been a bit soft. I had new brake fluid and pads and all cleaned up inside and out but they still felt a bit soft and not very good.

It was a 180mm front and 160mm back. I recently put a 203mm shimano ice-tech disc on the front and its incredible. The lever feel isnt soft anymore and I get to feel the biting point and get a solid lever which is how I like it. I got new brake pads front and back at the same time

The back however is still a bit soft. The only treatment the back hasnt had is a new disc. I dont really want to spend more money on a new disc so I was going to put the 180mm from the front onto the back.
The problem here was that the front and rear post mount adaptors were both exactly the same. So i was a bit confused and left it as the 160mm.

Has anyone else had this issue before. I really dont understand how/why the disc would cause the problem. Its a solid stainless disc so shouldnt have any give in it.

Also whats going on with the rear post mount. Do I need a 203mm adaptor. I not too up on the post mount adaptors and standards.
I know theres some called IS but I dont know what that means really Laughing

The Artist · Super Spammer Joined: 06 Jan 2008 Karma :

Have you bled them recently?

steven_191 · Nearly there... Joined: 31 May 2009 Karma :

No I only bled them when I did the pads before. The feel was the same after.
Still the same after these new pads so I made sure the fluid was topped up and its still the same.

The only other thing is the disc but it doesn't make sense. I think I might just deal with it because not having a really strong rear brake is a better option. I just feel like I have to pull it to get anything out of it. Compared to the front brake which just works with ease. (now)

benyboy · Two Stroke Sniffer Joined: 24 Jun 2013 Karma :

I had this problem too, found a small leak on leaver.
over time it sucks in air and brakes go soft. The leak was a pig to find. Re did seals and not had a problem since, u can do a quick fix by turning bike upside down and pumping brakes, don't know haw but dose work let me know if u need any more info

Entertwainer · Trackday Trickster Joined: 13 May 2013 Karma :

soft disc brakes are usualy down to air in the brake line.
when bleeding the brake, flick the lever gently, this can knock the bubbles that get caught up in the lever just before the reservoir.

other than that, you're better off getting the brake off the bike and hooking it up so that the caliper is directly below the lever. i mount mine on some spare bars on a work stand, and hold the caliper below the lever when bleeding.

this tutorial shows how to do it quite clearly:

https://www.youtube.com/watch?v=dFuwoEYvt_w

make sure the reservoir cap is seated properly before tightening - use the rolling technique when replacing the reservoir cap (this ensures no air is trapped when placing it on top - this video shows what i mean:

https://youtu.be/Lye3FCz_x-c?t=2m34s

also make sure your discs are centralised properly with the calipers/pads - it may feel soft due to one pad hitting the disc before the other.

if it feels soft after that then you may need to replace the hose.

but it all depends on what you mean by soft. LX brakes are rock solid (i think the ones you have may be M585 combi brake/gear levers) i have the M585 brakes only and they still feel a little soft, but i can lock up the rear (and front) wheel if needed still.