Issues with Xt rear brake squealing SOLVED SEE POST 35!

[discofrank]

Hey all, need your expert help

After bleeding my rear xt brake ( giant trance ) for the 1st time! the other day i went out for a ride and
had massive issues with it squealing and barley working

bleeding was done from the bleed nipple up, with a syringe and mineral oil pushed from the caliper up the master cylinder with the cup thingo in the reservoir
the feel after this was fooking awesome! nice and firm with all the spongey feeling had gone

now i had thought i might have got some oil on the pads or even some brake,parts and degreaser on the pads ( no not the stuff that evaporates! )
so today i went and got some new rear pads today and gave the rotors a good scuff up with some emery paper on both sides
also bought the better brake and parts cleaner that evaporates! and gave the rear rotor a good clean with it after i scuffed it up

and what do you know, the issue is still there!!!!
bike squeals even worse! and it barley slows down with the rear!

any ideas??

ohh and here is a short vid where you can hear it!
yer yer dont worry about the crash at the end! i know what i did wrong

https://www.youtube.com/watch?v=WrhoHaIRgS8

 

[moorey]

Contaminated. Cook pads and clean rotors.

 

[dunndog]

Contaminated. Cook pads and clean rotors.

Agreed. New pads AND rotors will reveal all. If you have power in the lever, you either have contamination at the other end, or there is something wrong with the mounting of the caliper.. I once had this on a dh bike, after 3 days riding it in nz howling like a wolf at full moon with haemorrhoids, I discovered the caliper mount on the frame had cracked. Mind you, this also caused huge vibration through the entire bike..

 

[discofrank]

Contaminated. Cook pads and clean rotors.

not to be rude but did you read my post??

i have BRAND NEW PADS and cleaned the rotors not only by sanding/scuffing them also with brake and parts cleaner

rotors are quite new and had ZERO issues before i bled the caliper

Agreed. New pads AND rotors will reveal all. If you have power in the lever, you either have contamination at the other end, or there is something wrong with the mounting of the caliper.. I once had this on a dh bike, after 3 days riding it in nz howling like a wolf at full moon with haemorrhoids, I discovered the caliper mount on the frame had cracked. Mind you, this also caused huge vibration through the entire bike..

could the piston not be moving square in the caliper?
no shuddering through the bike
doubt there is anything wrong with the mounting but i will look as i have just recently had to start using my au falcon to transport the bike as i lost the work ute , could have damaged something
find this a bit too much of a coincidence as it happened the same day i bled the brake but hey ya never know

 

[ChrisJC]

If you haven't done so already, find a decent length downhill and ride down with your brakes just touching the disc to build up heat and bed the pads in. Do it several times and see if that improves things.

 

[teK--]

i have BRAND NEW PADS and cleaned the rotors not only by sanding/scuffing them also with brake and parts cleaner

no no no no no no

do not sand your rotors.

clean the rotors only with alcohol; other treatments can leave residue or will destroy the rubber seals around that area.

once you have cleaned everything properly, align the caliper, make sure all pistons are moving freely then bed the new pads in.

 

[moorey]

not to be rude but did you read my post??

i have BRAND NEW PADS and cleaned the rotors not only by sanding/scuffing them also with brake and parts cleaner

rotors are quite new and had ZERO issues before i bled the caliper



could the piston not be moving square in the caliper?
no shuddering through the bike
doubt there is anything wrong with the mounting but i will look as i have just recently had to start using my au falcon to transport the bike as i lost the work ute , could have damaged something
find this a bit too much of a coincidence as it happened the same day i bled the brake but hey ya never know

I read. Maybe there was oil in the rotor vents. Maybe a dribble from your nipple is still there. Don't sand pads. 1, it won't remove contaminant, 2, it's unnecessary and will take ages to bed in again. Clean them really well. Clean whole caliper without pads in. Cook the pads...you may have contaminated straight away.

 

[Elbo]

rotors are quite new and had ZERO issues before i bled the caliper

I think you answered your own question. You may have inadvertently cross contaminated your new pads from the rotor. Isopropyl alcohol is your friend here. Spray rotors with alcohol and burn them. Clean with a fresh rag and you should be good as gold.

 

[The Duckmeister]

Contaminated. Cook pads and clean rotors.

NO!!!

Glazed pads most probably, especially if they're resin compound. Scuff pads on sandpaper to remove any manufacturing residue, leaving the dust on the pads. Go & pull some (as in at least 10) good hard braking efforts, without fully stopping. You need to get that brake pad dust into the rotors.

Never ever EVER clean the rotors with anything more than a hose unless you are absolutely, utterly, eleventy million per cent sure you've got oil on them; you'll strip off the embedded pad material then you have a sure-fire source of noise.

 

[pink poodle]

I think you answered your own question. You may have inadvertently cross contaminated your new pads from the rotor. Isopropyl alcohol is your friend here. Spray rotors with alcohol and burn them. Clean with a fresh rag and you should be good as gold.

Minlak! Finally found your second account...be wary frank, fire fire is not always your friend. Are you ready for a disco inferno?

Duckdude, what is the best way to avoid/reduce chance of glazed pads? A female friend loves to constantly drag her brakes, the resultant noise is fucking annoying. It's like an orgasming seal! Should I recommend sintered pads? My current advice of "get off the brakes" seems to be not sinking in and I'm a terrible coach.

 

[moorey]

NO!!!

Glazed pads most probably, especially if they're resin compound. Scuff pads on sandpaper to remove any manufacturing residue, leaving the dust on the pads. Go & pull some (as in at least 10) good hard braking efforts, without fully stopping. You need to get that brake pad dust into the rotors.

Never ever EVER clean the rotors with anything more than a hose unless you are absolutely, utterly, eleventy million per cent sure you've got oil on them; you'll strip off the embedded pad material then you have a sure-fire source of noise.

With respect, I'm disagreeing Duck Dynasty. I'm talking a wipe over with metho. I have to do it now and then if swapping to rotors than have been hanging on shed wall, or dragging out the DH bike after months without use. The wiping with metho removes dick all embedded material, but freshens up (otherwise they DO squeal occasionally). I'm running shimano on 8 bikes between me and the family, I do this to all, and always have brakes working minty. Brakes are as good as ever after less than a minute of bedding in, and NEVER squeal.

 

[Nambra]

I'm going to agree and disagree with both Moorey and the Duckmeister; no disrespect to either of you as your sage bike wisdom has educated me immensely.

I use isopropyl alcohol to clean rotors and I don't see how that can remove material that's been bedded in as a result of heat and friction, and a light sanding of pads does no harm either other than requiring you to bed them in again as Ducky says. I've had caliper alignment situations where the pads overhang the rotor slightly and you end up with a ridge on the top edge of the pad as it wears - only sanding will knock that edge off. Just make sure the sandpaper held firm on a nice hard, flat surface to ensure a good flat pad face.

Back to discofrank - I'm going to suggest that your calipers might be out of alignment, such that your pads don't sit parallel to the rotor, or that one pad is making contact before the other. The noise in your video sounds more like vibration/resonance than friction squealing to me, although I am listening on shitty laptop speakers. Are your old pads showing signs of uneven wear, front to rear, or is one pad more worn than the other?

I'd also be checking the usual suspects too: warped rotor, loose rotor bolts, loose caliper bolts, sticky brake cylinders.

 

[link1896]

The original degreaser you used, what was it? I suspect it has contaminated the pads. Pads are somewhat porous and have probably soaked up some of this degreaser.

 

[Minlak]

Minlak! Finally found your second account...be wary frank, fire fire is not always your friend. Are you ready for a disco inferno?
.

Silly Poodle you know your my second account....... Stirk is my third..... or is Stirk your second i forget it gets confusing...

Back on topic.... We cant have a brake fight with out at least one...


HOPES!!!!

 

[moorey]

I'm going to agree and disagree with both Moorey and the Duckmeister; no disrespect to either of you as your sage bike wisdom has educated me immensely.

I use isopropyl alcohol to clean rotors and I don't see how that can remove material that's been bedded in as a result of heat and friction, and a light sanding of pads does no harm either other than requiring you to bed them in again as Ducky says. I've had caliper alignment situations where the pads overhang the rotor slightly and you end up with a ridge on the top edge of the pad as it wears - only sanding will knock that edge off. Just make sure the sandpaper held firm on a nice hard, flat surface to ensure a good flat pad face.

Back to discofrank - I'm going to suggest that your calipers might be out of alignment, such that your pads don't sit parallel to the rotor, or that one pad is making contact before the other. The noise in your video sounds more like vibration/resonance than friction squealing to me, although I am listening on shitty laptop speakers. Are your old pads showing signs of uneven wear, front to rear, or is one pad more worn than the other?

I'd also be checking the usual suspects too: warped rotor, loose rotor bolts, loose caliper bolts, sticky brake cylinders.

All the bottom suggestions would be more feasible if he'd done something other than change pads. The sanding he have them will slow down the re-bedding, but I don't think it will cause the squeal and lack of power mentioned, and seen in vid. Years ago I had to lightly sand a rotor...can't remember why....but it really-bedded within 5 minutes of good solid braking.
Agreed abour sanding pads to remove ridge. I bought a set of XT's off a very prominent burner a couple of years ago. A month old, he complained they had no power. I pulled out the pads, and only about 1/3 was contacting the rotor, and had worn about a mm step in the pads, leaving 2/3 brand new. Not naming and shaming, but it's a mistake only the 1% of seasoned riders would make.

 

[stirk]

*sniparoo*

it's a mistake only the 1% of seasoned riders would make.

8mm socket doohickey :behindsofa:




As mentioned degreaser sounds like the issue. Keep that shit away from bikes.

 

[moorey]

8mm socket doohickey :behindsofa:




As mentioned degreaser sounds like the issue. Keep that shit away from bikes.

No qualms I know dick all about mattocs....but in my 17th year running shimano brakes, and know what has worked for me. :drama:

 

[discofrank]

The original degreaser you used, what was it? I suspect it has contaminated the pads. Pads are somewhat porous and have probably soaked up some of this degreaser.

was a brak/parts/degreaser hence why i changed the pads! and gave the rotors a good clean!
with the PROPER brake and parts cleaner the one that evaporates quickly and only the rotor OFF the bike so no chance of the stuff getting on the pads


there is no vibration that i can tell, as after i changed the pads etc i was riding on a footpath! smooth surface etc , when i get home ill dig the old pads out and see if there is uneven wear

also IF i have to pull the caliper apart or the pistons etc what grease if any do i use on the pistons?
i know with cars its rubber grease but they use dot 4/5 etc brake fluid not mineral oil

cheers all the suggestions keep em coming

 

[moorey]

Clean well with metho, or isopropyl if you're rich. Use a bees dick of shimano mineral oil, I believe...anything else could damage seals. I've only had to do one piston in all these years, and that dud the trick. I didn't remove Pistons, just extended them, used a tiny bit of oil, worked piston in and out, and cleaned off any spare oil.
I still don't think sticky piston is your issue though.

 

[Nambra]

Wouldn't be jumping into pulling calipers apart discofrank - all you did was bleed your brakes after all and it would be a shame to waste that nice fresh mineral oil!

You should be able to see whether you have a sticky piston just by looking at as you operate the brake lever. An easy way to free a sticky piston up is to simply cycle the piston through an exaggerated range of motion. Remove the wheel and brake pads, place a thin block about 3 mm thick (plastic is good) between the pistons and apply the brake to move the pistons out - whatever you use as a block needs to stop the pistons from popping out completely and be careful if only one piston is moving. Release the brake lever, remove the block and use one of those brake separating wedges to push the pistons back in. Repeat a few times and hopefully the piston frees up.

We're all probably assuming that your new brake pads are identical to the old ones in terms of pad material - is that right? Going from resin to metal might result in a bit more noise, and have you bedded the new pads in properly?

Edit: ^ what he said too