- News
- Reviews
- Bikes
- Accessories
- Accessories - misc
- Computer mounts
- Bags
- Bar ends
- Bike bags & cases
- Bottle cages
- Bottles
- Cameras
- Car racks
- Child seats
- Computers
- Glasses
- GPS units
- Helmets
- Lights - front
- Lights - rear
- Lights - sets
- Locks
- Mirrors
- Mudguards
- Racks
- Pumps & CO2 inflators
- Puncture kits
- Reflectives
- Smart watches
- Stands and racks
- Trailers
- Clothing
- Components
- Bar tape & grips
- Bottom brackets
- Brake & gear cables
- Brake & STI levers
- Brake pads & spares
- Brakes
- Cassettes & freewheels
- Chains
- Chainsets & chainrings
- Derailleurs - front
- Derailleurs - rear
- Forks
- Gear levers & shifters
- Groupsets
- Handlebars & extensions
- Headsets
- Hubs
- Inner tubes
- Pedals
- Quick releases & skewers
- Saddles
- Seatposts
- Stems
- Wheels
- Tyres
- Health, fitness and nutrition
- Tools and workshop
- Miscellaneous
- Tubeless valves
- Buyers Guides
- Features
- Forum
- Recommends
- Podcast
Add new comment
15 comments
After reading all the replies and being able to find more specific videos (because I understood a bit more what to look for), I have made progress.
This 6 minute one is useful https://www.youtube.com/watch?v=4C9R_H_GLKI
includes the easy pressure release option mentioned by HP.
The problem I found was more of one of the pistons sticking, so I have got that going a bit but more work needed. Fitting the park tool in took a knack but I was glad of it.
The rotor truing tool was easy to use as you can apply force with control, so I tweaked that a bit.
Still need to address the piston issue but maybe in the new year.
My first time with discs too so take this with a pinch of salt!
Sometimes it's not the caliper or the rotor or the pads. My Malt G2X fork is on its way back to Merlin because, after me giving up trying to get my front disc brake to run without contact, the workshop I took it to advised me that the fork was out of alignment and the brakes would never be right using it.
The pad ajustment spacers are effectively a feeler guage to centre the caliper as the pistons are operated....useful for setting up but if your pads are not retracting enough and "rubbing"...I'd suggest a bleed. Many people bemoan mechanical disc calipers but to be honest we get far less bother with the dual piston ones in the workshop than Hydraulics. Obvs the usual stuff is squeal... feel etc which can usually be sorted with new pads/decontaminate... your set up sounds like a set up issue for centring/bleeding out... can't tell 100% unless seeing it.... good luck getting it sorted
I agree, always start with the basics first and bleed the brakes with the pistons fully retracted using the shimano bleed block to ensure the right gap. I know a lot of people try to get a better lever feel by bleeding the brakes with worn pads still in situ or by shaving a mm or two from a bleed block, but this is a fine art that can create a problem later on when the new pads are fitted.
If you are going to true the rotor, my advice would be to have a go with an old one first as you can quite easily make things worse.
If you are then trying to centre the caliper using something like a Birzman Clam or similar then I have had better success by not squeezing the lever to hold the caliper steady, this only helps to centre it as to where it wants to sit by the pistons rather than centrally about the rotor.
Good luck....
I think the tools are useful for centering, but the gap will return to what it currently is. After all you pushed the pistons back by hand, and then after applying the brakes the gao was back to where it had been before, so why would it be different with a saocer tool?
I was sure I had posted a thanks earlier.
I have also ordered a rotor park tool as a christmas present (otherwise I won't get anything !)
There's not usually any gap adjustment on disc brakes per se. One thing I've tried when fitting a new disc, is to undo the top bleed screw at the lever and then push the caliper pistons back in with the pads still in place. When the gap is suitable, replace the top bleed screw again - the theory is that there's space for a bit of fluid to escape if there's too much in the system.
Otherwise, you can try truing your discs so that they're within 0.5mm of true.
As a heavy rider (90kg) living next to the Jura in Switzerland, I get a lot of brake wear and piston issues. This is what I have found works for me - all my brakes are shimano, maybe sram are different -
1, even if you don't wash your bike it is worth running cold water through your brakes to rinse out dust. You could also use brake cleaner spray, but water is less horrible for the environment.
2, whenever I wash my bike, I take the pads out first (worth mentioning a tiny dab of copaslip on the thread of the pad retaining pins to stop it from sticking). Then I use a toothbrush to wash around the shoulders of the pistons. If they are sticky or very dirty, I use a spacer made of a few old links of chain in between the pistons and pump the brake level to make the pistons move further, make sure you use a spacer as if they go too far you are in trouble. Then I use thick cotton string like floss round the base of the pistons. Then push the pistons back in, a special tool or a plastic tyre lever avoids damage to the pistons. If you keep some old pads handy you can also use them to protect the pistons while you push them completely in. If you sense any stickiness, pump them out and push them back again. the two pistons should move the same amount on each lever pump.
3, Put the pads back in, wheels in, then pump the levers until the brakes work and you have good lever feel.
4, spin the wheel and listen, any scuffs reveal the rotor is out of true, so use a special tool or a clean adjustable spanner to bend the point of the rotor which scuffs. You only need to apply a tiny amount of force, better to make lots of tiny adjustments than risk taking it too far and having zig zag rotors. You can normally see which way you need to go by shining a light between the pads and looking for the missing gap.
If I have a really sticky piston, I have found lubricating it carefully with the oil shimano use as brake fluid can help clear the crud out. But you need to be really careful to avoid leaving oil which could contaminate the pads or disks.
Starting point is that if they are too close, they won't move out by themselves. You would normally prise them apart with a spacer tool or flat bladed screwdriver (trying not to score the pads, hence the tool) the idea being that this pushes fluid back into the reservoir.
If the brakes have been over-filled, then you can't always get the pads to retract. In that case I'd expect very little play in the levers.
Not messed with GRX levers, so not sure on what tricks, but as a general observation some systems are tricky to get set up with the right amount of fluid - too little they can be spongy, too much, they don't release.
Worth looking up the Shimano dealer manual which is publicly available.
Spacer tool would work but assuming you haven't got issues with sticky pistons/seals and don't have rotors that are out of true too much
Have ordered a spacer tool. No obvious kinks.
But if it all self adjusts, how does the spacer work ?
Shimano are quite good at publishing their service manuals...
https://si.shimano.com/pdfs/dm/DM-GADBR01-01-ENG.pdf
(I think that's the right one - p12 bullet point num 9, and p92)
Sounds like your pistons aren't perhaps retracting enough? How long have you been running them? Could the seals around the pistons need a squirt of silicon spray so they can slide back a bit easier?
Only since may.
I did take it back for a tune up and mentioned the unevenness, but the shop did not resolve it.
I do have some silicon spray.
Back to your LBS I would go. That's if you can get it in the workshop at this time of year.