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Caliper is Shimano MT400 and pads Shimano B05S-RX.
I pushed the pistons back as much as I could and there is probably 0.5mm left to go in but I don't know how to get that last 0.5mm. Remove fluid ? Easy to do? (I don't normally get involved with brake fluid as it's always a absolute catastrophe)
My main is issue is that even with the last 0.5mm I can't see how the rotor would fit, it needs more. How can that be?
Those brakes have always been the most dead travel free brakes I have ever experienced and now I can see why.
Are there different pad thicknesses??
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I had this the rear on with my old SLX M666 brakes when swapping from worn stock Ice Tech pads to Uberbike Finned pads.
This is how I fixed it:
-Removed new pads
-Adjusted the lever so it was flat/level
-Removed the bleed screw and covered the hole in paper towel
-Gently pushed the pistons fully back into the calliper
-Refitted pads
-Refitted bleed screw
-Readjusted lever
Looks like they need a bleed. It's not really that hard to do. You just need to get hold of the kit and some fluid. I normally do a bleed around every other time I change the pads. If you're really not keen to give it a try you'll need to take it to a shop.
citizen lee has the answer - the system is over filled which is why the pistons will not go back all the way
I'm with citizenlee on this - I've done the same. There's probably a bit too much fluid in the system. I doubt they need a bleed.
Level the master cylinder, undo the bleed port a turn or so, then push the pistons all the way in using the old pads and a screwdriver/spanner/whatever. A bit of fluid will come out of the bleed port, but not much and the then you will have gained all the pad space possible. Tightened the bleed port and reinstall the new pads. Fingers crossed you will have just enough room, if you are using shimano rotors. If you have thicker rotors, then probably not.
beaten to it! What citizenlee said.
I’ve done the “open and squeeze” method before, but getting some fluid and the screw in funnel costs very little and makes the occasional bleed a very easy job. Before someone (on this forum) pointed me in the right direction I used to force the pistons back without opening the bleed port… and wrecked the seals in brake levers. Don’t do that!
Try refitting the old pads and then use these to protect the pistons as you use a large lever to gently try and work the pistons all the way in - .5mm per side should give enough space for the rotor if using standard thickness discs.
If they won’t go in any further then use a size 10 torx and gently unscrew the fill/bleed screw on the master cylinder (on the handlebar end) whilst aligning it as level as possible. Try levering the pads/pistons again then as soon as they’re in put the screw back in, including the “o’ ring that’s either stuck to the screw, dropped on the floor or still in the hole!
You should now have room for the new pads. Hope this helps.
Beaten to it by faster fingers, but, I don’t think a bleed is necessary - that’s a different symptom - just a few drops of fluid need losing. Also, I can’t emphasise this enough, always use old pads whilst pushing the pistons back in. It protects the pistons from damage (some are plastic) and it helps them go back in straight.
had this the rear on with my old SLX M666 brakes when swapping from worn stock Ice Tech pads to Uberbike Finned pads.
This is how I fixed it:
-Removed new pads
-Adjusted the lever so it was flat/level
-Removed the bleed screw and covered the hole in paper towel
-Gently pushed the pistons fully back into the calliper
-Refitted pads
-Refitted bleed screw
-
Readjusted lever
There is a simpler way of getting the pistons back so you can insert the wheel* :
Insert a big arsed screwdriver between the pads and twist it like a bastard. There will be resistance initially, but if you persevere then there will be a loud pop from the brake lever and the pistons will easily push back into the caliper....
You can then wipe the copious quantity of brake fluid off your son's face and fit the front wheel without any issues.
* Note that brake functionality may be somewhat impaired.
Fit 1 new and 1 old as a quick fix
Try refitting the old pads and then use these to protect the pistons as you use a large lever to gently try and work the pistons all the way in
I'd suggest that if you think the system might be over filled it's worth undoing the bleed screw on the reservoir before doing this. If you add too much pressure you can damage the diaphragm in the master cylinder which will be much more faff to fix than just taking 30 seconds to loosen the screw. But yeah, look out for that o ring!
Thank you all! I followed the process and no fluid seemed to have come out so I tried to suck some out with the paper towel 😂.
Or maybe air came out?
Either way there is now *just* enough space. Lucky that the rotor is perfectly straight.
All very tight yet no rubbing so job done.
I'll try the other caliper tomorrow 😂
@thegeneralist does my kind of maintenance.
Perhaps you could start a youtube channel?
Update. This is my GF's bike. She runs her brakes UK style. I run my brakes continental.
So I tried the rear just now (no need to highlight the unintended pun). Same issue predictably. So I applied the same process.
Except that I open the front lever screw thing again instead of the rear. And plenty of fluid came out.
So I had a perfect front which is now not working as the lever goes to the bar.
THIS is why I never get involved with fluid. It is a catastrophe every time. Every time.
Absolutely fuming with myself. Might buy an entire new front brake as cheaper than using the shop.
Before doing the lever thing, clamp the lever shut overnight - lever as close to bar as possible. Any air in the system will move upwards to the lever overnight. Release the lever and slowly release the lever...it should feel firmer if there was any air that has now moved upwards.
When you do the lever thing and push pads out any air should be ejected as well as any excess fluid.
It won't get rid of all air, but it should help move any air up to the lever.
If it's just a bit of fluid from the master cylinder, you can do a lever bleed only to fill up what came out. Have you got a bleed cup and mineral oil to hand?
The last time I got involved with fluid on my bike, I had to repaint the ceiling.
I know it's irrational and I see myself as an excellent bike mechanic as I can do anything else or do a frame swap to perfection in a couple of hours but I refuse to do hydraulics as I can guarantee the outcome, a total mess.
I know it's absurd and irrational but it is what it is.
At least the rear is perfect now, almost as perfect as the front was earlier today 😂
Honestly, it's a no mess, 5min (max) operation! Definitely not spraying the ceiling with fluid! How did you do that anyway?
Bleed them (both).
It is possible that there is an air bubble(s) in one or both systems.
If there is a bubble (possibly in the hose) it may compress slightly when you push the pads back in but it is still air in the system so unless the air got out somehow the pads will creep out as the air expands/bubbles join together / temperature changes.
I am 99% sure that this is why I ended up buying a bleed kit while on holiday the other week. A pad change dislodged that air into the lever rendering my rear brake unusable. Previously I had let out a dribble of fluid in an earlier pad change because of exactly what the OP describes.
In terms of retracting the pads I think what happens is the bubble compresses slightly but as soon as you remove the screwdriver/tyre lever it returns to its neutral uncompressed state leaving the pads out a bit.
Then you let a drip of fluid out and maybe dislodge the bubble as well so you lose a drip + the air bubble. Suddenly the fluid is down further than just the drip.
I had sprayed the ceiling with oil as I was trying to use a syringe attached to the lever for the rear without having opened the rear caliper. Basically there was nowhere from the fluid to go so the all syringe shot into the air spraying the oil with it.
Anyway, I just used the syringe again but without the plunger, basically as a cup and loads of bubble have now been replaced by mineral oil and the front is perfect again. It took 5mn indeed so thanks for pushing me outside of my comfort zone.
Inspector Clueless of Sussex
Good to hear the front is good again!
Out of interest, do you know if the brakes were previously bled by anyone? If it's done with old/worn pads in situ, you can end up in that situation.
I remember getting bleed blocks included with my 2019 bike purchase (for that reason), but it doesn't seem to be a thing anymore (my Chisel didn't come with any, neither did the replacement Deore brakes that I purchased).
Fit 1 new and 1 old as a quick fix
This. Pull all the pads from both calipers. Bin the two most worn. Fit one new and one worn pad to each end. Give it a few good rides to bed them in and wear them down a bit. Fit the two new pads to the front and the two old ones to the rear.
Good to hear the front is good again!
In no small part thanks to your encouragement Yak.
I hardly got any bubbles out of the rear but I think it's because of the routing of the hose (internal) and the kinks that make meandering sections potential traps despite moving the bike to a quasi vertical position with my third hand.
Still the rear is now good but even tighter than the front, there is basically practically no clearance and again only possible because the rotors are perfect, for now 😂
But it makes for an incredibly sharp braking feel although modulation isn't great as you can expect.
Oms: the brakes haven't been touched since it arrived new from Canyon 5 years ago, hence the new pads as the old ones were practically down to the backing plates and crumbling.
Thanks again all and apologies for my somewhat flippant and dramatic approach to what should have been a simple job 😕