Anyone know anything about disc brakes?

Give the rotor a sand and clean then make sure you bed the new pads in properly.

This.

A really good clean, otherwise pads may get contaminated again (or get new rotor is the surface is showing wear).

And don't hold onto the brakes when you come to a full stop to prevent burning out the pads.

My rear brake has stopped working completely and started squealing uncontrollably. Also I can pull the lever right up to the bars now and no amount of pumping will make it bite again.

So I'm guessing contaminated pads, leaky calliper and air in the system?

New caliper time.

Rim brake time.

I have been rimming a bit much recently, you're right, I'll take a breather.

It's Deore anyway, bought second hand from a mate...
Now the real question is, do I bother setting up everything myself or do I throw money at the problem?

Have you checked the pads? :) they could be run down to the metal backing...

Might be worth a punt.

Also: is it possible to swap front and rear callipers? I've got a working deore front calliper kicking around in the parts bin that I could swap out. Would bring the cost down to new discs + pads + bleed kit.

yes. calipers are (usually) not specific, adapters can be.

Got a photo of the caliper with the rotor? Give the rotor a wipe with your finger and see if there's any oil on it also check around pistons. If there's noticeable amount on either then it's probably a leak.

The disc and pads could be saved depending on the amount of wear on them.

what levers are you using with the JuinTech R1s? Ive tried with TRP RRL levers and they feel very spongy with little power. Way worse than the Shimano CX75 I had previously using the same cable and outers!

Alfine Di2, they feel great with the TRP compressionless cable kit .. no spongy feel at all.

I still think they are the closest to a full hydro setup.

thanks. any recommendation for a suitable single speed drop bar lever? not sure why the TRP RRLs arent working well. Its like they dont draw enough cable.

the only way i've got them to work at all is by pre-tensioning the lever arm to bring the pads closer to the rotor and then tightening the brake cable, but this gives very poor braking power indeed.

thanks. any recommendation for a suitable single speed drop bar lever?

The SRAM S500.

There's an adjuster for that, I use mine with SRAM Apex levers and obviously compressionless outer.

Can you not adjust the pads on those brakes without moving the arm?
You want the full range of motion in the arm on the brake or it is indeed going to be very poor

Yup, they have an adjuster because there's no self adjustment.

There was a set of these in shelter charity shop in crystal Palace a couple of weeks ago. Looked to be in decent nick

Yup, they have an adjuster because there's no self adjustment.

This.

Work like a normal caliper brakes, which TBH is ideas, as we do get way too many customer who think their completely worn out brake pads and rotor is fine because it "doesn't feel worn".

Fucking Hy/rds.

Thanks for the SRAM s500 recommendation

I'm a little confused now... They have an adjuster on the arm that changes the amount it can travel but there's no way to adjust the pads inwards? (Like on cx75 or bb7 etc)

The adjuster on the arm is for pad wear, it moves the pads closer to the rotor by moving the piston in further. If your pads are over half worn you may be at the end of adjustment, mine came a bit underfilled and you needed to start with new pads with a few turns on it, I keep meaning to bleed them and add a touch more fluid to the system, but I'm lazy and just stick new pads in.

Issues on a brand new bike, bought from a currently unnamed online retailer. SRAM rival hydro brakes. As the brakes bedded in, the front became noisy. It's still very effective at stopping, though, and the rear brake is perfect.

I took it to an unnamed local bike shop who said it was set up fine, and any noise would be contamination and should burn off. I didn't agree, but didn't want to be a pain for them, so contacted the unnamed online bike retailer again. They said it'll be because I'm using the wrong type of pad (resin versus synthetic). That's obviously nonsense, and I'm no closer to working out what the issue is and then making the online retailer pay to fix it.

I took a video of the noise the other night. Does anyone have experience with this type of noise? Apologies for the panting, it was after going up a big hill. https://www.amazon.co.uk/photos/share/QRuXt6T8SvvsCOpvNyN3YkWFhHWIbPucpuHl2Z7x7wq

Find a river bury it thats what hope said to me , after that they where bedded in and worked great.

Hope famously used to take jars of mud with them to service brakes at World Cups. Smear the rotor in the mud go do some stoppies and like magic pads are bedded in and squealing stops.