Lack of power on my Shimano 4 pots.

Bleeding only helps with a spongy lever feel. If the levers are solid, they probably just need bedding in. As they are used, I would clean the rotors with alcohol or with dish detergent and very hot water, then lightly sand them. Remove the pads, replace them if they're badly worn. Otherwise, clean them too and lightly sand the surfaces. Reassemble and find a big hill. Get your speed up to 20 kph or so, then brake hard until you drop to walking pace, keep repeating this. After a dozen or so cycles, you should feel them start to bit much harder.

Assuming there are no leaks, should I try new pads? Disks too?
What should I go for with pads and discs, these are fitted at the moment?

I'd take the rotors off and give them a good scrub with washing up liquid and a nail brush. Pads, washing up liquid, rub the contact surfaces together until no more dirt\brake pad dust coming off then scrub with nailbrush. if you want to be very thorough then naked flame on the contact surface (gas hob, camping gas stove or similar) until no more dark smoke coming off.

Agreed, sounds more like contamination than bleed. My 2 pot XTs were leaving me cacking myself a few weeks back on some big slabs in Squamish. Pads out, sand back with fine paper, left in isopropyl alcohol over night, a couple of passes over a burner, cleaned rotors thoroughly with degreaser, then alcohol. Find a big hill, drag the brakes all the way down, then quench at the bottom to bed back in. Seems to have sorted it!

Another potential issue, check that the pistons are moving equally. They get a bit sticky so clean them up with a cotton bud and brake fluid, cycle them in and out a few times, clean, cycle, clean, cycle etc until they're clean and moving freely. Make sure you wipe off the excess fluid before you refit the pads.

Cheers, will do the cleaning thing as a start then. I've lubed the pistons and all seem to move freely.
What make pads if I need some more?

I've got those on the ebike, which with my middle aged bulk means im stopping 105kg. Rear has a micro leak which I've not as yet bothered doing anything about and provided no braking force,so am just using the front and that stops me just fine.

If yours arent performing I'd look towards bleeding or new pads/rotor clean up because otherwise I would rate these as pretty good.

Ok thanks, I'm surprised how bad they are tbh!

So what make/type of pads folks please....!?

Cheers

I use Uberbike.
Race Matrix seems to last well with heat and bite hard. Noisy at times.
My older Kevlar were better alrouders. They bite more gently, but have loads of power with a touch of heat in them and quieter.

On our road/ gravel bikes I am having less positive experience with Uberbike organic - they just seem noisy and need a dose of heat before coming on stronger.

The type of pads really won't make a huge difference. You should have plenty of power with those, if you don't then it's not the pads.

My default is Superstar Organic or Sintered these days, good price and performance balance.

I must admit I'm not 100% sure what a "gravity bleed" is. I usually find a proper bottom-up bleed pushing the fluid from syringe at caliper to funnel at lever keeps mine feeling good. Be sure to wind the lever in and out and get all the little bubbles out of it.

DiscoBrakes.com Sintered pads for me.

Much cheapness when you buy 4 sets.

As said, it's usually contamination of rotors\pads that leads to loss of power.

kingstop sintered from aliexpress

Race matrix are usually a good all rounder. Although going into slop I find them less good. I’d run sintered pads for the winter - Uber bike ones are ok and cheap. But on my sram codes the best lads I’ve used are the genuine sram sintered ones.

Cheers again.
Ok, rotors & pads scrubbed.
I've bled the rear again, gravity & syringe, used a bit of fluid lol. Also this time wound the reach adjust, cheers chaka, I'd forgotten to do that....
Still hardly any bite so I'm thinking the piston seals have maybe gone...
Front bled fine with plenty of bite.
I've zip tied both levers to see how that goes.
Will check for leaks on the rear brake later or tomorrow but...

Anywhere got 520 or similar calipers going cheap at the mo?

Thanks.

So, zip ties off and both brakes felt good. Next day with bike not moved and stood in wheel stand, the rear, not so firm.
So bleed funnel reattached pinged lever a few times as I'd done with the original bleed and more air bubbles present . Nice firm lever. All good.
Roll on to this afterron, lever softer again. I'll check pistons for leaks in the morning. Do seals in the levers go as well? I couldn't see any moisture there.

Cheers

Check your pad wear. Shimano move past the optimum servo wave position before you get to the backplates.

Do seals in the levers go as well?

Oh yes. Repeatedly. Theres no actual dirt seal on the end of shimano master cylinders. It relies on being shielded by being nestled into the lever body, but its perfectly possible for dirt to work its way in and score the piston bore, which results in micro leaks at the lever end.

Red panda components did a dirt seal kit for it last year, but, well, they were Russian and we know whats happened since then.

Funnily enough I was wondering about pad wear so I'll try that first cheers for tip.
I've just ordered some Superstar pads (20% off at mo) as well as some cheap ones off Aliexpress.

Checked again today.
Lever coming back further to the bars again. Attached funnel and air bubbles again.....pinged lever and adjusted reach screw which got the air out, for now.
No fluid that I can see coming from the lever so it must be the piston seals?