hey, happy new year. this is my first post having recently joined the world of mountain biking. bought a second hand orange evo4 the day before christmas eve, been out on it a few times over christmas in the birmingham alps… if you live within a 20 mile radius of brum you may have heard my discs squeal. the squealing is bad, so bad i have considered facing almost certain death by not applying them at all. anyway, i was thinking of removing the pads and applying copper grease between pad and piston, will this solve the problem or should i be doing something else. cheas.

They all do that sir – well hopes especially have a bad rep for squealing but any brake can do it – worse in the cold and wet.

Coppaslip on the back of the pads might help – as might sanding down the pads and the discs and rebedding in. A chamfer at 45 degrees for a mm or so on the leading edge of the pad can help as well.
facing discs mounts for is mounts and centreing pads properly might be another thing to try

Thats one thing you can do. Another is to remove the pads and rub the braking surface onto something slightly abrasive to remove any potential contamination. Once you have done that I would try and make sure that your callipers are line up by undoing the post bolts, pulling the brake lever on and whilst holding the lever on re tighten the bolts to position centrally.
However with the weather being as wet as it has it could just be that the water is causing the problem and you need sintered pads.

Some brakes (most notably older Hopes) do that all the time, even in the dry.

ALL brakes do it when wet sadly… And seeing as due to either snow or rain, it's definitely not been dry anywhere in the Midlands (I'm in Worcester so not far from you) to my knowledge, that could be why your discs are squealing!

Bit of copperslip BETWEEN the pad back and the piston (not on the pad surface as I once saw somebody do! Seriously!) won't hurt though I suppose.

What brakes are they? And are they IS or Post mount type? Might be that the brakes need re-aligning or the disc mounts facing too, but until you've ridden them after cleaning them, and in dry conditions, I wouldn't worry too much about it to be honest.

they're hydraulic shimanos, original fitment. as for IS or Post? ain't got a clue, said i was a newbie! thing is a couple of mates were in front of me, they were on their brakes too (much newer & larger discs!) but weren't clearing the woods of wildlife. think i'll go to the garage, wash the mud off and have a play.

The main thing is to set up the caliper so the rotor runs true in the centre. Have a look on the Hope website where there is a video of how to set up disc brakes. If second hand you may need new pads – buy sintered for Shimano as their resin pads don't last long. You may also need to bleed the system (mineral oil for Shimano) and fully clean the calipers. A little silicone grease on the pistons will help to stop any problems with lazy pistons etc. Be wary of copperslip on the back of the pads as it will wash off gradually and may then contaminate the pads/rotor. Also clean the rotors with meths or disc brake cleaner at regular intervals.

they're hydraulic shimanos, original fitment. as for IS or Post? ain't got a clue, said i was a newbie! thing is a couple of mates were in front of me, they were on their brakes too (much newer & larger discs!) but weren't clearing the woods of wildlife. think i'll go to the garage, wash the mud off and have a play.

My apologies, forgot you'd said you were a newbie. Obviously I take it from your knowledge of braking systems though that you've some experience with cars or motorbikes?

Anyway… Yes, go have a good clean… Take the pads out, give em a rub down with some sandpaper. Spray everything in brake cleaner. Wipe everything off then go for a ride. Should do the trick to be fair.

Shimano brakes have in my opinion always been about the most squeal free brakes out there. That said, on my ride two days ago through the mud and the snow, my Shimano LX brakes were squealing like pigs because they were constantly wet and muddy!

Incidentally, your shimano brakes are probably Post Mount.

have knowledge of cars and motorcycles with single, twin and four piston calipers and both fixed and floating calipers or discs.

cleaned these shimanos up earlier, quite surprised that they were twin pistons. initially they were squeal free, then i cleaned the disc and they squealed again! only had wd40, solvent cleaner and some crap three-in-one copper grease (it's a spray grease and goes everywhere… not ideal)

gonna get some new pads, brake fluid, cleaning materials and proper grease tomorrow to do the job properly.

as for IS and post mount, IS is "international standard" and applies to disc mount but what is "post mount"

That should illustrate the difference between IS Mount and Post Mount for you hopefully…

Don't bother bleeding the brakes unless they feel spongy. Shimano brakes use Mineral Oil rather than DOT, which doesn't tend to go spongy anywhere near as quickly in my experience.

Give the pads a thorough going over cleaning them… And get them hot if you can! Get a pair of tongs, hold them on a hotplate or over the gas hob for a few seconds if possible… This will burn off any contaminants (be sure the windows are open though of course).

Just give the rotors a good wipe, then reinstall everything and go ride… It probably won't be totally squeal free yet. What you need to do now is find yourself a BIG hill, preferably a straight, on road slope, and go as fast as you can… Then start dragging the brakes all the way down… This will get them mighty hot, the pads will bed back onto the rotor, and leave a deposit on the rotor of clean pad material, which helps with braking performance and stopping squeal…

See here and here for more details from Shimano themselves…

What model brake is it that you have anyway?

Oh, and if they do need a bleed, I've got all the gubbins to bleed Shimano Brakes with if you need…

i see, the only info i pulled up on international standard related to 6 bolt disc mount and yes i am post mounted.

calipers are br-m 525 on 160mm (ish) rotors.

rear was spongy before and since i worked with the bike inverted, school boy style (though i did refrain from putting a clothes peg and piece of card in the spokes) the lever now hits the bars so will defo need bleeding.

thanks for offer of gubbins mboy, i might take you up on that as as yet i have no bike specific kit.

update;

after several experiments problem is solved and it's pretty simple.

cleaned calipers and rotors with brake cleaning spray, new pads, align calipers to rotor everytime wheels are put back in (might be overkill but it's easy and works), after dirty ride clean bike with soap and water and wash down with hot water hose, spraying plenty around brakes.

don't bother with copper grease on back of pads and make sure no oil or grease (wd40) gets on rotors or calipers.

no squeal and plenty of bite.