Help in adjusting my disc brake..

Oh and I’m sure the black marks on the Freeza disc rotor are just streaks of dirt from pad wear that have been blown through the fins. I don’t notice them on my Dura Ace rotors (because they are black!)

PP

Definitely a sticking piston. You need to get that sorted before doing anything else. If you take the wheel out, take the pads out and then VERY GENTLY squeeze the lever to see the pistons move you will be able to see which one is not moving as much. I must emphasise that without pads and a rotor between the pistons you have nothing to stop you pushing the piston clean out of the caliper so even a very light squeeze on the lever will cause this.

I’ve had this before and the only way to free it off was to clamp the free piston with a flat piece of bar and a clamp holding that piston in, then operating the lever to cause more pressure on the stuck piston. This got it moving, but it did pop out and I subsequently needed to bleed the brake fully again.

Once it is moving you can then clean the exposed edge of the piston with alcohol and cotton buds etc to remove anything that has built up and caused it to stick. When clean, if you haven’t blown it out of the caliper exercise it back and forwards gently by pulling on and off the lever gently. Remove the bar/ clamp from the other piston and exercise gently to see if they are now moving together.

With this done you can force the pistons fully apart and then replace the pads and wheel and align the caliper using the two mounting bolts, your white sheet of paper and your mark one eyeball and hex key.

If (and it sounds from your post above) you have a ‘tink, tink, tink’ sound as the wheel rotates with the caliper correctly aligned it sounds like you have a disc that is not true. Using your white sheet of paper as a background behind the caliper (and it’s easier with the bike upside down to see) rotate the wheel and watch for any side to side movement of the disc rotor as it spins. This will be causing your tinking sound as the buckle in the disk makes contact each revolution with one of the pads.

Look at a video online of disc rotor trying to see how to do it, I’d use the proper tool or a quality adjustable spanner, not a pair of pliers. If you open your adjustable spanner, and then close the jaws around the disk rotor (just like if you were grabbing it with your pliers) you will have two nice flat surfaces in contact with the rotor. No need to pad the jaws out. If you use pliers, depending on the type, they tend to have serrated teeth and a gap for grabbing round things and then a pair of cutters at the base of the jaws! You stand a good chance of damaging your disc using those.

So, with your spanner attached to the disc it is simply a case of bending it towards or away from you to straighten it as required. Obviously you have to apply the bending force at the right point and in the right direction. Do it gently to start with and you will get a feel for ‘that’s not enough’ as you bend it but it makes no difference. Better to do it again adding a bit more force each time until it has the desired effect. To find where to apply your ‘spanner’ spin the wheel and stop it where the rotor comes into contact with the pad, this is usually easier to do by ear to start with, then narrow it down by turning the wheel back and forth around the ‘tick’ of contact. When you have the wheel stopped at exactly the point when it is making contact and you can see which side it is bent towards, you now need to rotate the wheel to get the offending area of the disc out of the caliper. You can do this by eye, or put a finger on the tyre exactly at the point where the area on the disc rotor is bent and move the wheel around without moving your finger - you can then run an imaginary line from your finger towards the axle and where it crosses the rotor is where you need to put your spanner to adjust.

It is a bit fiddly, but pretty easy once you understand what you are trying to do. Once again I would encourage you to ensure that there is not too much fluid in the system by putting the bikenthe right way up, remove the bleed screw and push the pistons in fully before refitting your pads and wheel.

if you still get noise after doing all this and after braking, chances are you have some trapped air in the system which is heating up under braking, expanding and causing the pads to be pushed closer to the rotor. As the caliper cools down the trapped air contracts and the pads release again. Had this a few times and on some models found it a pig to remove all the tiny trapped bubbles despite following the correct bleed sequence. The elastic band around the level over night can help here.

PP

I've had hub axle ends start to unscrew before, double check the ends / adapters are on tight and with some Loctite. Sounded a lot like what you're describing.

You need a specific tool to check that the rotor is tight. Its the same tool used to remove/tighten a Shimano cassette. If you don't have one then if you have a bike shop handy its a 5 minute job for them, or a 2 minute job if you take them just the wheel. Good luck and hope you get to the bottom of it.

Mine can develop a rub after lots of braking (fairly new Shimano callipers). 

I understand if there is air in the system then it can expand when the system heats up, resulting in pads pushing outwards slightly and starting to rub. Unfortunately when the system cools down again they don't seem to want to retract, it's almost as if they have re-adjusted themselves.

Seems like seals and pistons need regular cleaning/lubing in order to keep the system genuinely rub free, and if the rub develops after hard braking it might indicate a re-bleed is required (or at the very least leaving the bike overnight with the levers pulled to the bars with a rubber band or similar, this pressurises the system and leaves a pathway open between the system and the reservoir on the lever which can allow trapped air to rise out).

Ah - maybe you've got a sticky piston? That could explain why careful adjustment of the caliper doesn't help too much.

A quick search brings up this: https://bicycles.stackexchange.com/questions/20931/hydraulic-disk-brake-piston-not-fully-retracting

Check whether your brakes use DOT fluid or mineral oil - mixing them is not a good idea and be careful about pulling the brake lever when pads and rotor are removed as that could push one or other piston out too far.

If you're reasonably careful you should be able to do that without needing to bleed the hydraulics (not difficult, but involves having a suitable syringe etc).

If the disc is moving under braking force, then either its not tight on the hub, or one of the pistons in the caliper is sticking.

If you hold the brake on tight and rock the bike back and forth, is there any knocking? If there is, can you put a finger on the disc and a finger on a frame part and feel if there is any relative movement?

If there is no movement from the disc relative to the frame, then if you take the caliper off and press the pads apart with a suitable tool (I find clean tyre levers work well) and then gently squeeze the brake lever, do the pistons and pads move out smoothly and equally, or does one stick?

Don't allow them to come out too far and don't squeeze so much that the pads meet - else you won't be able to get the pistons back in without removing the pads.

Okay, sounds like your wheel is good and solid, so I'm puzzled as to what could be moving to affect the braking. Maybe the rotor has some movement in it, though that's unlikely if the lockring is anywhere near 40Nm.

Not bedding in disk brakes can lead to them being noisy and not having the full stopping potential, but it shouldn't result in a periodic clunking noise.

You mentioned about the wheel moving inwards under braking with the bike off the ground - I don't see how that can happen unless something is a bit loose.

Was there any movement at all in the rear wheel when you where checking it out yesterday?

For the problem to resolve and then re-appear sounds to me like something is slipping/moving.

It shouldn't make any difference if the back wheel is on the ground or not. However, the crucial point is that there shouldn't be any movement in a back wheel (except for the obvious rotation), whereas I suspect that you do have some play in your rear wheel.

When you get a chance, remove the thru-axle, have a look at it and then re-assemble and see if the rear wheel has any play in it.

You probably won't need to bend the rotor - that's only required if something has made it go out of true or it's quite old. I've never needed to do mine.

The black lines being on each of the rotor fins sounds like something is causing that, but I can't think what.

Oh and the black lines on the rotor just look like muck to me, possibly it has run down when the bike was stationary.

PP

Rear wheels don't spin as well as front wheels due to the extra drag from the freehub - in my experience anyway.