Anyone know anything about disc brakes?

The only thing brakes can do to stop your front wheel moving is pads, retainer clips or caliper touching the rotor. The caliper would only touch if you had missed a spacer or washer and would sound like a horrible metallic scrapy sound. Retainer clips sounds similar and could have been knocked out of place in transit or with wheel re-insertion. you seem to have elimiinated pads already.

OK, I'll take the pads out and put back in again...

Actually I didn't do that, I loosened the caliper and retightened it, I think I just didn't have it on straight.

Seems OK now, panic over!

Is it always necessary to face a brand new frame ahead of fitting new discs?

It shouldn't be. Bike manufacturers should be doing this. My actual experience, however, is that it's almost always beneficial

I'd rather wait to find it's shit, most mounts are straight enough

Nice one, thanks. It’s a SS Evo 4 Hi-Mod so hopefully it’s alright but what do I know eh

One thing about discs. We were told that less spokes are better. Rim brake wheels either 16 / 20 etc. Now it's OK to have many more. So were we lied too, was that old 32 spoke set of training wheels fine all along? Was any 1600g set of wheels fine no matter how many spokes? Im ignoring aero for the sake of this discussion.

ignoring aero

Reduced drag was always the only material benefit of lower spoke count.

Just set up a new Fairlight Secan with Rival disc brakes and new pads. Rotors not completely new, but very little use. When I engage my rear brake, I get a humming noise/vibration throughout the F+F. It isn't a sound from the rotor itself, but from vibrations maybe through the fork/headset? Any ideas?

Shimano.

Fork/headset shouldn't vibrate with rear brake. Maybe isolate the problem first

Wanted to go from 180mm to 203mm on the rear of my GSD. Stupidly bought the wrong adaptor (need 160 - 203, not the 180 -203 that I bought).

I used the bolts that came with the wrong adaptor as my existing ones were knackered anyway.

So, I have a 180 - 203mm Magura post mount adaptor going spare in CR7 if anyone needs/wants.

I was alway under the impression that Shimano road levers and MTB calipers were compatible? I've setup some GRX-400 levers with some old(ish) single pot SLX. They sort of work, but even after a fresh bleed the lever pulls to the bar and they're not very powerful at all. Am I missing something with different lever throws, or something?

No, they work together. Maybe a poor bleed, try again with the pistons most of the way out (careful they don't come out, find something to use as a thin bleed block) to make sure there's no air trapped behind them, if still no good tie the levers down tight and leave it for a few hours or overnight and check again.

Could be an air bubble trapped somewhere. Hold the bike up in front of you and bounce it up nd down on the rear tyre whilst pulling and releasing the lever.

Any trapped air bubble will make its way to the reservoir at the top of the system and brake should instantly feel better.

Finally, Bleed brake to remove air bubble.

You can get a bit more fluid in the system, to reduce the lever pull.

Push in through the bleed port with the syringe while depressing the lever slightly.

Open bleed port > squeeze lever a bit > press syringe > close bleed port > release lever.

Cheers @Ben689908 not sure I have enough hands but will have a go! Do you do that with the bleed funnel on?

Nice one @MTB-Idle and @snottyotter will also try that.

Without the bleed funnel. You only need a pair of hands - no need to rush between all the steps.

Fluid doesn't compress so if it's full it's full, any extra you get in the system due to hose expansion or piston movement will end up back in the reservoir or leaking out the lever, you can reduce the bite point by squeezing the lever with the wheel out so the pads sit closer to the rotor to achieve a similar thing but all these things reset as the pads wear and it returns to normal. It should work fine if it's bled properly and nothing is broken though, levers going back to the bar doesn't sound right. I like to bleed from the caliper up to the cup to take any bubbles with, then back to the syringe, if it doesn't work back and forth a couple of times then tie the levers down and try again after a decent break

Let’s not forget who ever designed most calipers was is an idiot. To gravity bleed Shimano flat mount rears you have to get the hose to the highest point of the caliper. So it’s rest the bike on its back wheel and back of the seat, oh no wait that puts the fill port on the bars in the wrong place… the best way I’ve found is unbolt the calipers and lay them on something to get them in the correct position, bleed them and then bolt them back up. Sound like a faff, but it’s way quicker than chasing air down a hose. Front ones are the right way up when on the bike.
It could of course just be me being thick.

I have a frame that has some new fangled cable routing through the stem/ steerer tube. Straight to biek shop to fit callipers, or have a go myself.

I’ve only ever changed disc pads and bleed Shimano GRX stuff.

Depends on how much time, money and perhaps crucially patience you have.

I'm the type to do it myself, spend way too much time, lose too much patience, and save hardly any money along the way...

... But I'll enjoy it and do it again.

Straight to bike shop I reckon then>>>>>>>

Sound choice. Just go to one you trust. as the labour hours can add up with internal routing. I've had a frame that took me 5 mins the first time, to +30 mins the second time I decided to do some maintenance.

Similar story with handlebars. I spent a good 45 mins trying to internally route a hose through a tiny hole and sharp bend, but when I figured out the best technique for that particular set, the next side was only 5 mins.