Not really sure what the problem is. Dreading it being the leaky seal problem. Or maybe it's contamination. Or worn rotors. Or worn pads. Or a combination of all three. I've got a new rotor sitting there waiting, and more new pads, although the current pads were new at some point in the past and didn't solve the problem. The problem wasn't solved with new pads so I dug out a slightly less worn rotor. Cleaned rotor with IPA then thorough rinse with water and wipe, heated pads with heat gun (not actual fire) and gave light sanding. Solved for a short while then problem returned. More heating & sanding, and more pad material came off quite quickly through sanding. Brakes work nicely for half a ride then next ride they're useless.
Problem being very noisy squealing brakes with poor power. No problem with front brake, just the rear.
Could over-loosening the bolt attaching cable to caliper in order to adjust the hose angle cause seal problems? (I stocked up on olives the other day so ready for that one).
Are there any diagnostic flow charts? What are the signs of leaky seals? Don't want to replace with new pads and new rotor if the problem is leaky seals. Cheers.
Problem being very noisy squealing brakes with poor power.
That should have been the first line of your post.
The flowchart is basically:
1. Are they noisy and/or lacking power? Probably leaky caliper.
2. Do you suffer from wandering bite point? Probably not properly bled.
I think those two points will cover 90% of cases. Spraying chain lube on the rear caliper probably covers most of the rest.
Clean and dry caliper. Dust with talc. Tie the lever off over night so the system is under pressure.
If there's damp talc in the morning, you have a leak.
Thanks I'll try that camp talc test. With toilet roll. Presume you have a bleed block in there.
While cleaning the calliper I found an alternative source of contamination: the bleed port still had oil in it from the last bleed I performed, enough that there was some in the rubber cap. The port itself wasn't loose.
I had this problem with my commuter bike. Replacing the caliper fixed it. It did happen again after a few months.
Replaced the brakes with non Shimano brakes and have had no more problems.
I did wonder if salt off the road was causing the seals to deteriorate?
If you've got a bunch of olives I might be tempted to swap the calipers front and rear to see if the problem moves. I doubt that oil under the cap covering the bleed port is the issue. Are you sure they're bled properly?
Leaky calipers. Sounds exactly what I had. Wasn’t even visible (didn’t do the talc trick mentioned above) but I’d fit new pads clean the rotor etc and lose power mid point in my next ride. Sent them off for warranty and they confirmed they were borked.
Has put me off shimano brakes
Fixed mine for 18p.
https://singletrackmag.com/forum/topic/shimano-transfer-port-o-ring-size/
Thanks, missed that one, that's interesting... Most threads I've seen recommend binning them, and the last thread I saw suggested repair cost and time not worth it. What model calipers did you have were they SLX?
I found my front one really susceptible to poor alignment.
Loosening it off and carefully aligning it and equalising the pads sorted it from louder than Motörhead to near silent.
Sounds like micro leaks contaminating the pads. New caliper time most probably. I don’t get why Shimano aren’t all over this and get it fixed.
If you confirm you've got a leak its not the end of the road for the claiper.
If it looks to be the oring at the transfer port you're laughing. Easy fix.
If you've got oil leaking from the piston seals it's likely that the seal groove is contaminated with dirt and corrosion. Split the caliper, force the pistons out with compressed air.. remove seals then clean the seal groove as best you can. I used a dremel and a nylon wheel with a bit of metal polish
https://drive.google.com/file/d/1VCb9JK2tZ2At5A_LHLGh5SqodbZw7r9e/view?usp=drivesdk
Reassemble.
Now bleed your brakes as shown below.
Those calipers in the pic must be ten years old. With a clean and that bleed method theyre working flawlessly. I can't recommend that bleed technique enough for the wandering bite point problem.
If you put new pads in, then ride immediately, is it ok?
Mine were, but then after leaving the bike for 24 hours they screeched, I concluded due to contamination. I tried replacing the transfer port seal with limited success.
I don't run any Shimano brakes any more, IME, Clarks ones are way more reliable for low end, hopes on the nice bikes are the spares supply means last for ever.
Ceept - exactly my issue. Change pads sort rotor out, new pads would be good for one ride.take the bike out 24 hours later and loss of power and screeching.
Appreciate you may be able to fix them but that’s beyond my skill set and as it happened in warranty period I didn’t feel it was worthwhile.
Still amazed that Shimano haven’t sorted the issue.
Whays it like when you put water on it?
Is it quiet and powerful when wet...but then turns into a useless horn when dry??
I had this issue a while ago.
Cleaned and sanded pads and disks..no change
Replaced.. pads no change
Replaced disk..no change
Replaced pads and disk together...perfect
It's worked fine for months...no clue what it was?
Replaced pads and disk together…perfect
That appears to have worked, been two weeks, been riding the bike a couple of times a week and no honking.
Gave the calipers a good clean including the bleed port which was full of oil. If micro leaks from the calliper can render the brake useless don't see why this couldn't be a cause either. Anyway all good now.
Knowing Shimano brakes they’re probably borked and require replacing because you can’t buy spare parts.
I got my bike out, a couple of days before a trip, and discovered the honkiest brakes known to Christendom.
Swapped the pads - nope.
Went to swap the rotors from another bike, then realised that 6bokts don't fit on centrelock.
Remembered I'd got a spare y bolt rotor and a centrelock adapter, so tried that - nope.
Considered taking a different bike, but discovered that this was also Mr Honky.
It appeared that all of my bikes had caught the honky disease (apart from the road bike - but he doesn't fraternise with the others).
Anyway, it was past shop closing time, so I resigned myself to new pads and rotors, when the shops opened again.
Next morning, I go the bike out, ready to strip the honky bits off, and discovered that the honking had completely disappeared (maybe the geese had flown south for winter?)
So, after all that kerfuffle & angst, I was able to complete a lovely 80km section of the KAW, without having to listen to much than the sound of true on gravel
Still completely baffled.
Still completely baffled.
Probably just dust and grime on the rotors if it'd been parked for a while. That'll burn off and the pads will bed in again.
Probably just dust and grime on the rotors if it’d been parked for a while. That’ll burn off and the pads will bed in again.
Posted 1 day ago
Except that the bikes had been ridden recently, and I'd tried bedding the pads in, the day before, to no avail
Got issues with my deores so will have another look at them tomorrow having read this.
Update/ressurection
There's been loads of these 'My Shitmano brakes are shite, what can I do?' threads but this seems to be the latest...
I've a pair of well used R785's that the rear has been noisy/poor braking for a while.
I blow lamped the pads to get rid of any contaminants
Cleaned the disc/pads/calipers/my testicles with brake cleaner
Bled and generally ****ed around with em...
Changed the transfer port o ring
Cleaned and lubed the piston seal groove/piston bore with nice red grease
Changed the piston seals as there seemed to be a bit of weeping (not from me)
Refilled and rebled
Looks like we might have won but tomorrow's 'back of pad' check will be the final test...
They are realy simple so if you've the time/patience/aptitude, saves chucking perfectly salvageable stuff away.
2. Do you suffer from wandering bite point? Probably not properly bled.
Sound the wandering bite point = bad bleed fallacy klaxon!
Wandering bite point is not the brake pumping up with expanding air, it's pistons not retreating back quick enough before the lever is pulled again.
The reason the marshy bleed works to sort the wandering bite point is that it LUBES THE PISTONS WITH FLUID and hence speeds up the pistons retreating back into the caliper..
Suggesting it's a bleed issue has left loads of people with perfectly bled brakes puzzled why their bite points are wandering about like one of the Walking Dead.
If you have wandering bite point and want to sort without doing a marshy bleed...
1) pop the caliper off the frame,
2)pads out,
3) clean the caliper with IPA,
4) pump pistons out, clean, lube with a bit of mineral out on a cotton bud
5) push back into the caliper
6) Repeat steps 4 and 5 a couple of times.
7) Clean with IPA again, no really clean it.
8) refit pads
9) refit to frame.
Experience states that it's worth doing even to brand new shimano brakes.
I had a new ultegra caliper leaking out of the box this week. It's the shimano way. I'd love to lash them in the bin but limited options on a cross bike with existing shimano groupset - at least on the MTB you can switch easier.
The reason the marshy bleed works to sort the wandering bite point is that it LUBES THE PISTONS WITH FLUID and hence speeds up the pistons retreating back into the caliper..
This is also a fallacy.
Piston retraction is only done via seal rebound. The pistons are quite strongly gripped - think about the force you have to exert to push pistons back in for new pads. No way that the suction from the lever spring is anything like as strong as that.
Pistons only slide forward. Lubing the pistons helps them to move forward nicely together (hopefully) and provides more resistance to dirt ingress.
What Science officer says.
it amuses and appalls me at the same time how misunderstood disc brakes are
Mtb brakes are so unbelievably simple. Whats missing is critical thinking from folk trying to fix/service them.
Instead of working through logically with consideration of how they operate, you get people doing 'things', but not understanding if its needed or not and how their action might affect whats going on.
Wandering bite point is not the brake pumping up with expanding air, it’s pistons not retreating back quick enough before the lever is pulled again.
The reason the marshy bleed works to sort the wandering bite point is that it LUBES THE PISTONS WITH FLUID and hence speeds up the pistons retreating back into the caliper..
As Scienceofficer points out, this is a fundamental misunderstanding of how disc brakes work.
Every time I've had wandering bite point on my own brakes, it's been cured by filling the system properly so that the reservoir doesn't have any air in it. It's not impossible that there are other causes, but Shimano brakes can be fiddly to bleed and get all the air out of the reservoir so this really should be the first thing to check.
Also, buried somewhere in Shimano blurb its stated that brake pads should be changed with 1mm of material remaining on the backing plate.
But what people do (including me) is run them down further which results in the pistons extending ever further and the lever reservoir partially emptying as the fluid fills the void behind the pistons.
Now theres insufficient fluid for the lever piston to actuate without ingesting air and hey presto, you get wandering bite point even with a fresh bleed if you have heavily worn pads.
The one thing we know for sure about Shimano's wandering bite point, is that nobody knows for sure how to fix every brake that does it.
But yeah, I agree on a proper bleed usually seems to do the trick.
Wellllllll. After New transfer port O ring and piston seals, I may still have a leak... Check again tomoz after more fiddling. 🙄
Also, buried somewhere in Shimano blurb its stated that brake pads should be changed with 1mm of material remaining on the backing plate.
Yes, if you know about it, it serves as a warning that your pads need changing.
Its pretty useful for that, and happily seems to coincide with power tailing off a bit - which I suspect is the servowave cam moving beyond its point of best mechanical advantage.
Its almost like someone designed them to be like this.
Wellllllll. After New transfer port O ring and piston seals, I may still have a leak… Check again tomoz after more fiddling.
Did you examine/clean and debris/corrosion from the piston seal seat?
Did you examine/clean and debris/corrosion from the piston seal seat?
I did. I fitted the seals with red grease rather than lubing with mineral oil tho so they could be a bit draggy until they cycle a few times. We'll see.
If not, I'll strip them out again and have another blast with the Scotchbrite...
Woo and indeed, hoo. Houston, I think we've solved the problem.
No wetness on the back of the pads today or squealing like a scene from Deliverance. We'll see how she goes but I have a firm lever, no wandering bite point (not that I had before) and no drippage.
Send all your incontinent Shimano calipers to me 🙃
Nice one!
I'd the problem on the new bike on the rear.
Thinking it was a micro leak ive posted here,there, everywhere until i bought new pads for the front, and after a clean put the slightly worn front pads in the rear.
The problem hasnt resurfaced.
I know the reason. Just after buying the bike the rear was really soft, so i dropped it off at the shop i got it from, who bled the rear and from a few days after that the squealing and no stopping power started. After changing it became obvious that the shop had left the pads in and performed a bleed, I imagine contaminating the pads/system.
So to be 100% sure its contamination and not this micro leak, maybe best to put pads from whichever caliper is working to test it,before splashing out on a new caliper.
But but, there's no need to chuck the caliper. Here's the bits needed to fix drippy jobbies:
The Piston seals are very hard wearing.. I've never replaced them when refurbing calipers. A quick clean and they'll be grand.
The problem has always (ime) been Fod in the seal groove.
