Squealing rear discs/pads... The Sound of Silence (now)

[redefined_cycles]

The Hydraulic v mechanical (I'd go hydraulic any day btw and having been a lover of BB7s for years, after going for decent hydros, the BB7s never felt quite that nice ever again) thread reminding me of my squealing pig syndrome on my bike...

Seems like a pretty new thing for me and never noticed it previously (but would have as its that annoying) so its defo new. For the last few rides, which there ain't been many of, I've been getting alot of squaling off back brake on the DHs. Both pads are the same (AFAIR) in that the front and rear are both the non sintereds from UberBikes.

Been using their pads for years without problems but I'm definitely getting a tiny bit of fade along with the squealing this time round. Could it bw that I'd not bedded em in on the last change or is my disc shot? I did note that the rear (squealer) was much hotter (sizzling) than the fronts!

Thoughts? Change pads and rebed? or swap out for new disc too (currently on what was an already used disc AFAIR during the initial build)...

Ta

[Bearbonesnorm]

Worst squealing I've ever had was with Shimano when the pistons / seals develop micro leaks. A change of pads and a good clean will cure it for a short while but it soon returns.

[ootini]

Worst squealing I've ever had was with Shimano when the pistons / seals develop micro leaks. A change of pads and a good clean will cure it for a short while but it soon returns.

I've just swapped the rear pads on my MTB to cure this howling and lack of power. Keeping an eye on it as I think I may have the microleak issue too

[Jurassic]

I take it that the squealer is on a mountain bike? You mention that you've not been riding much lately and I've found that if I leave my mountain bikes unridden for a period of time (which has been happening a lot since I got my gravel bike) the brakes feel really wooden and are really noisy when I get back on them again. I don't know if this is some kind of oxidation happening on the brake pad friction material when the bike's not being used, that's my guess but it is only a guess. I've had this happen on three different bikes using three different types of Shimano brakes (XT two pot, Saint four pot and XT four pot all with varying pad types, OE and aftermarket). These are all very powerful brakes using big rotors and have been working perfectly when I've put them away and they end up barely stopping me and squealing horrendously. The answer is very straightforward though fortunately, just put some mud and water on the rotor and ride it a bit, you'll get horrible grinding noises for a while but within a few minutes the brakes go back to normal (I'm assuming that the dirt is acting as an abrasive paste and cleaning the oxidised material off the pad surface). If I don't do this the brakes remain noisy and lacking in power for much longer. Not sure if this is your problem Shaf but it's gotta be worth a try before you start pulling the brakes apart.

[Alec]

Are they shimano?
Ive had this problem a few times with shimano brakes, i tried changing pads but it kept coming back, i even changed one of the calipers which cured it for a while but then it came back after a time. I think its the micro leak problem as ive just had them apart and can see oil on the back of the pad and these have been sayt in the spares box for over a year.
This has happened on both zee and deore and ive had friends with the same problem. Sadly the only way to solve the problem for me has been to use different brand brakes.

[TheBrownDog]

Worst squealing I've ever had was with Shimano when the pistons / seals develop micro leaks. A change of pads and a good clean will cure it for a short while but it soon returns.

Best squealing I've had was in 2018 when the Chilterns Winter Bivvy crew departed the pub. All our brakes were cold and wet and sounded like shrieking banshees. We tried to play We Wish You a Merry Christmas, but it went wrong fast. Sure the locals loved it, it being Christmas and all.

[redefined_cycles]

Are they shimano?
Ive had this problem a few times with shimano brakes, i tried changing pads but it kept coming back, i even changed one of the calipers which cured it for a while but then it came back after a time. I think its the micro leak problem as ive just had them apart and can see oil on the back of the pad and these have been sayt in the spares box for over a year.
This has happened on both zee and deore and ive had friends with the same problem. Sadly the only way to solve the problem for me has been to use different brand brakes.

Yup... m7000 slx. I'm on a ride now and wiped em with mud as well as torqued em up a bit more... no loss of power (just fade when too hate). The tightening seems to have helped a bit. Will keep an eye and might dismantle at some point if it doesn't get better

[Alpinum]

Seems like a pretty new thing for me and never noticed it previously (but would have as its that annoying) so its defo new. For the last few rides, which there ain't been many of, I've been getting alot of squaling off back brake on the DHs. Both pads are the same (AFAIR) in that the front and rear are both the non sintereds from UberBikes.

Been using their pads for years without problems but I'm definitely getting a tiny bit of fade along with the squealing this time round. Could it bw that I'd not bedded em in on the last change or is my disc shot? I did note that the rear (squealer) was much hotter (sizzling) than the fronts!

Sounds a bit like glazed pads.
Too much heat on the system will cause this.
When I chat about overheating brake systems there's always a dick shouting "you're braking wrong" or "brake less" having no clue where and how I ride. But still, there is a point in this.

In your situation I often sand the pads and rotors which helps, but until I swap rotors and/or pads it's often reocurring.
Larger rotors and more heat stable pads make for a long lasting difference in my cases.

Sintered pads cope better with heat, but lack the responsiveness (intial bite) in the wet and tend to be louder in the wet when not hot (imagine very wet and not steep descending with only little braking).
Some organic or semi metallic compounds are better than others, sofar my best experience with pads have been the e-bike pads from Swissstop.

Bedding in is crucial. I used to give a sh!t about it, just put them in and continue descending like berserk. Nowadays I think it's well worth taking my time and I go by this:

"Step 1. On a gradual downhill slope, drag each brake for 20-30 seconds, alternating between front and rear. Repeat 2-3 times.
Step 2. On a steeper slope, engage and drag the brakes for 10-15 seconds then increase lever pressure until the bike slows almost to a complete stop. Repeat 2-3 times.
Pro Tip: The front pads will have been heated more than the rear. To achieve optimal performance, exchange the front and rear pads then repeat Step 2.
CAUTION before replacing or exchanging brake pads it is essential to let all parts cool."
From here
https://www.swissstop.ch/brakepads/disc ... sc31/disc/

Different pad types/manufacturers may go with different ways of bedding in.

Larger rotors make a very big difference. In power and heat management. They are not just for DH racing. Go 20 mm larger. It'll take much more to get good pads with large, floating rotors overheated that OE pads and regular, thin steel rotors.
Ashima Flotor ARF-3 has been great, good heat management, can be bent back easily after striking rocks, are lightweight and the price is okay too for a floating rotor.

[redefined_cycles]

Thanks veey much Gian (Alpinum) for that comprehensive reply. I too had briefly considered that I've not properly bedded em in but discarded it as 'just a thought'...

Will see about bedding in some new pads (or sanding these ones down) as I dont think I spotted any leaks thus far... no excess pull on the lever either which I'd imagine would have been if there'd been fluid leaking out over the last few weeks...

Ta all and will keep updated as to how I gets on

[Bearbonesnorm]

Will see about bedding in some new pads (or sanding these ones down) as I dont think I spotted any leaks thus far... no excess pull on the lever either which I'd imagine would have been if there'd been fluid leaking out over the last few weeks...

Shaf, with a microleak you may not see any real sign of fluid and it'll likely have no effect on the lever feel.

[redefined_cycles]

Will see about bedding in some new pads (or sanding these ones down) as I dont think I spotted any leaks thus far... no excess pull on the lever either which I'd imagine would have been if there'd been fluid leaking out over the last few weeks...

Shaf, with a microleak you may not see any real sign of fluid and it'll likely have no effect on the lever feel.

Plan is this Stu... When I get em off the bike to try and give em a squeeze and pop the pads out a bit to see if theres any signs of fluid. At same time I'll sand down the rotor and either swap the pad or sand it down...

Hopefully it's just a bedding in issue as I think I remember swapping the fronts en the BB200 but the rears after that.. meaning they've not really had much use to have been able to bed in between uses. Besides theres no proper gentle hille (well none that you'd enjoy riding down on mtb steadily) around these ends... they're either all out or not at all (or off road... where its a bit of a pain bedding in pads!).

Lets see how I gets on when I manage to investigate

[techno]

Will see about bedding in some new pads (or sanding these ones down) as I dont think I spotted any leaks thus far... no excess pull on the lever either which I'd imagine would have been if there'd been fluid leaking out over the last few weeks...

Shaf, with a microleak you may not see any real sign of fluid and it'll likely have no effect on the lever feel.

Plan is this Stu... When I get em off the bike to try and give em a squeeze and pop the pads out a bit to see if theres any signs of fluid. At same time I'll sand down the rotor and either swap the pad or sand it down...

Hopefully it's just a bedding in issue as I think I remember swapping the fronts en the BB200 but the rears after that.. meaning they've not really had much use to have been able to bed in between uses. Besides theres no proper gentle hille (well none that you'd enjoy riding down on mtb steadily) around these ends... they're either all out or not at all (or off road... where its a bit of a pain bedding in pads!).

Lets see how I gets on when I manage to investigate

I had the micro-leak problem with my first set of Shimano deore hydraulics from very soon after I fitted them. New pads and disc cleaning would solve it for a week or two then the problem would return.
I Binned the shimanos and ran bb7s for a while. Now running a new set of slx which are ace. No problems so far.
Also, for bedding in I have found that, with organic pads, a normal ride is plenty (road and easy xc, no downhill lunacy).

[Alpinum]

Whilst quite a few mention the leak problem with Shimano, I wonder if this issue is only related to older pre 2012 brakes?

I can't remember a mate or myself having such issues with newer Shimano brakes. Using 3 sets of XTs and SLXs from 2017 and 2018, my girlfriend also has some newer SLXs and we've never had leak issues with them. One had a sticky piston and most have a slightly shifting bite point (first pull of lever the bite point is closer to the bars then after repeated pulling), but otherwise I like them. Loads of brake for not so much money.

Yet, before I put SLXs on my everyday/travel bike I had some second hand Deore on it (came from another second hand bike), the rear had a leak issue at the piston, but it would, once well cleaned, take a few days to leak enough to contaminate the contact areas again. This Deore must be from 2010 or so. The squeeking was of a lower pitch than that of glazed pads. Kind of... also brake power with contaminated pads is very, very poor, whilst a glazed pad is just enough off to realise that there's something wrong.
At least in my experience.

[Alpinum]

Thanks veey much Gian (Alpinum) for that comprehensive reply. [...]

Ta all and will keep updated as to how I gets on

Very welcome Shaf.

Eager to see how you get along, hoping you get it solved without any fuss.

[redefined_cycles]

Quick update whilst I wait for the missus to go and come back (she just learnt from her mate that there's an elderly lady up the road who's been told to stay in lock down until June and she has Covid... so she's gonna knock on to see if she needs any bit of support). Done the pads and rotors sanding down thingy and checked for leaks. Not sure if I could check for micro leaks by just pumping the pistons in and out but seems theres at least no macros leaks.

The pistons are made out of some resin (looks like white plastic) material and pushed back in nice and easily. Hopefully - after trying to follow the brake bedding in to the dot which I normally never do properly - I should see an improvement on the squall (or lack thereof)...

[Bearbonesnorm]

The pistons are made out of some resin (looks like white plastic) material

Phenolic resin Shaf.

[redefined_cycles]

The pistons are made out of some resin (looks like white plastic) material

Phenolic resin Shaf.

Thanks Stu. Thought you'd know... Why the move away from proper alloy stuff that the older pistons have always been made of. Seems very fragile to me (although it did seem to pop in without issue I did feel the need to be extra careful that I don't groove (whats the word again) it...

[Bearbonesnorm]

Why the move away from proper alloy stuff that the older pistons have always been made of.

It's cheap, easy to produce and doesn't conduct heat that well.

[redefined_cycles]

Followed the bedding in (almost) to the dot (which I should be doing anyway but you know...

Even stopped to let the brakes rest during the middle of the process as the descent was too rocky and steep to be able to have any decent control with just the front brakes for even a little while

Squelaing all gone thankfully...

Thanks all... Gian, ta once again (I owe you some brakes )

[redefined_cycles]

Quick update as the squealing came back but now: sheer silence...

After bedding in properly the sound went a way briefly but then was back the next day. Noted the step in the 160 ice tech rotor and measured up at 1.6mm thick (apprently 1.5mm is the limit). So rode over to Huddersfield and picked up a 180mm ebay bargain. Non IceTech.

Swapped rotor over for the 180mm and left the pad in (just a quick skim with sandpaper, saving money, controlled testing). Went out for a ride and bedded everything in but after some time (less than an hour) the squealing was back yet again.

Lever travel still fine, so I stopped midride and swapped out the pads to try and eliminate any contamination issues/controls (ie. A controlled test). Suddenly after a few bedsings (it's not a word, I know... but might be one day) in, no squealing - like a pig - from back or front. Sorted I thought and since it was a nice 25ish miles left I had plenty time to bed in and assess...

End of ride, squaling back but not like a pig. More like a humming. Front still totally silent so I must've not been the pads!! Next day on short ride with baby, humming still there on the rear brakes. Like a buzzing but at slow speeds.

Gets home - or maybe I'd already done this bit the day before, not sure - and remove the rear pads. Pop in bleed block with some plastic or summat and then give lots of squeezing at the lever. To try and force any micro leaks to show up. Not sure if it was the smartest move but nowt. Lever travel still fine and no obvious leaks. Threw some silicone grease around the pistons for good measure.

Humming still there on slow speeds so gets back home. Removes the old pads (rear.. but they were on the fronts for last 400ish miles, remember I swapped em out on a ride or 2 ago). Measured up the pad thickness and still had life but changed em anyway (one side at around the 1.6mm and the other on 2mm). Centred the caliper to the rotor. Gave the disc a good wipe with DB cleaner. Centred it all up again and tightened the bolts.

That was last night, day before eid. Went out today. Did the 10 to 15 stops suggested on the Uberbike pads packaging.

10 miles in and still TOTAL SILENCE. Happy days. No squealing or sqaulling or humming or buzzing substandard brakes. My faith in Shimano restored and my sadness at Avid subsfandard remaineth.

Thanks Stu...

Thanks Gian...

Thanks everyone...

Apologies to any walkers who might have had to endure 'that noise' for any length of time (please dont tell your dog to poo on the trails to get 'the bikers*' back).

*Apparently its a local thing which some local walkers told me about when I was cleaning the poo off my tyre. Its all over local FB they said!!

[RIP]

Worst squealing I've ever had was with Shimano when the pistons / seals develop micro leaks. A change of pads and a good clean will cure it for a short while but it soon returns.

Best squealing I've had was in 2018 when the Chilterns Winter Bivvy crew departed the pub. All our brakes were cold and wet and sounded like shrieking banshees. We tried to play We Wish You a Merry Christmas, but it went wrong fast. Sure the locals loved it, it being Christmas and all.

I remember that! It was brilliant