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I have a set of Shimano brakes. They are a bit odd in that although brand new they appear to be an OEM set and so consist of M445 calipers and levers which are similar although not identical to M595.
Riding last week the lever throw gradually increased to the point of hitting the bars before there was any braking action. The pads were worn but not worn out so I bled them yesterday. I don’t have the proper bleed spacer so having removed the pads I used a plastic block I had. To get this in I had to push the callipers back but then it fitted. I bled by adding mineral oil to the top reservoir and draining from the calliper end as directed in this video:
There seemed to be very little air but I carried on and bled all the fluid through. Putting it all back together and the wheels on the lever feel is solid but there is still quite a lot of throw before the pad hits rotor, the calipers pistons return quite a lot every time. Any ideas how I can improve things to get a faster bite (there is no bite point adjuster)? My thoughts on how to improve the situation are:
1. New brake pads. Cheating really but increased thickness would mean faster bite point. This would mean the 2nd half of every set of pads would be wasted though!
2. Bleed again but with narrower bleed spacer. This would bring the pads out further as their natural resting point but might make getting new pads in difficult
3. Use some more complex bleeding operation such as forcing fluid up from the calliper and all the sorts of things Clay does here:
Number two. kind of.
If you've moved the pistons back to bleed then reassembled, having to pump the pistons back out to the original point means you've pumped more fluid down the hoses.It may just need a top up in the master cylinder. Worst case is another bleed.
Sticky pistons
Point 2 will give yo a temporary solution but it will get worse as the pads wear again. what is happening here is the pistons are not self adjusting as they should. YOu need to lube the pistons with mineral oil.
I've got the same brakes - two pairs in fact, one on each bike! They are 'Alivio' level, the hint is in the model number - anything M9xx is XTR, M8xx Saint, M7xx XT, M6xx SLX, M5xx Deore, M4xx Alivio.
They are also pre servo-wave, so do tend to have a fair amount of travel in the lever before they bite, and unfortunately being entry level, don't have the stroke adjustment some of the more expensive ones do.
However, the rapid progression to hitting the handlebars you describe shouldn't happen, and sounds like air in the system or a sticking piston. And, your solutions 1 & 3 won't make any difference, but 2 is a temporary fix until the pads start to wear and it'll revert to normal.
I've come to accept that entry level brakes will always have compromises and have decided to upgrade to the latest SLX - there's a great deal on them at Evans at the moment!