Got a Genesis Core 30, Shimano BR-M445 (Alivio) callipers and BL-M505 (Deore) levers. I’ve got an ongoing problem with the brakes squealing and complete lack of power. Done the following so far to try and rectify it:

Cleaned and sanded the pads in case of contamination.
Cleaned and sanded the rotors again in case of contamination and also to remove existing pad material.
Bled the brakes, top down and also bottom up, very confident there is no air in the lines.

After all this I went down the nearest big hill a number of times to bed the brakes in. At first they were squealing like crazy but after 3 or 4 big stops the brakes finally came good and there was plenty of power and no squealing. Success! Or so I thought…

That was 3 weeks ago and today was the first chance to get back out on the bike for a proper ride, immediately it was obvious the problem had returned as again the brakes were squealing and there was no power. WTF? Why would the problem be resolved and then return? The bike hasn’t been used at all in this time.

This is driving me mad. Had a whole day of biking planned today which has now been abandoned 🙁

Any help appreciated.

I have had no experience of your particular brake setup but what pads are you using? Some brakes can only run resin pads and what fluid are you using?

Stock Shimano pads and Shimano mineral oil. Thanks.

sounds like shimano seal weap to me

common as hell

thanks to shimanos spares policy a new calipers the only remedy for it 🙁

the telltale sign is the brakes were good when you put them away and they were contaminated when you used them again.

Take the pads out and hold them ove a gas cooker flame with some pliers. in my experience that’s the only way to completely remove any contaminants from the pads. I do it fairly regularly with my pads as they get contaminated easily if its wet.

Sometimes they end up feeling better than new.

” I do it fairly regularly with my pads as they get contaminated easily if its wet.”

does it rain oil on your trails ?

Are there any signs of leakage?
I have the same brakes and had leak at the caliper end of the hose, due to a wonky olive.
Worth a look and easy to fix.

Been fine since.

I had the same brake set up on my core 30 I found that they just didn’t have enough power also try opening the res cap on the leaver slightly pull the leaver if you see bubbles coming up there will be a small hole in the res and you’ll need to replace it. If I was you id upgrade to something better I have Hayes Carbon On my core now an there 100 times better

OP I have the exact same brakes and have had the same problems as you in the past. I bought an extra set of pads and rotate them after every ride making sure I clean the pads with IPA and sand the surfaces after every ride. Do you notice your pads are glazed after each ride?

I found that they just didn’t have enough power also try opening the res cap on the leaver slightly pull the leaver if you see bubbles coming up there will be a small hole in the res and you’ll need to replace it.

Surely this just denotes air in the system, nothing to do with holes in the reservoir? IMO the M445’s perform perfectly adequately if they are set up correctly.

Are there any signs of leakage?
I have the same brakes and had leak at the caliper end of the hose, due to a wonky olive.
Worth a look and easy to fix.

Not that I can see. I’ve just been pumping the lever with a bleed block between the pistons and there is no sign of a leak or bubbles etc. I’ve also checked round the reservoir and the hose but again nothing.

OP I have the exact same brakes and have had the same problems as you in the past. I bought an extra set of pads and rotate them after every ride making sure I clean the pads with IPA and sand the surfaces after every ride. Do you notice your pads are glazed after each ride?

Well this was going to be the first ride in a number of months, however on checking the pads they do look a little glazed:

However, they were working fine after the test ride 3 weeks ago when they came good after bedding them in. This was 3 or 4 stops from 25mph on each brake.

I’d say you may have a leaky seal. I had some m550 levers with an m760 caliper. Lever pull felt firm, but no power. Replaced the hose, the lever and still no improvement. After a long bleeding session I noticed a very small bit of fluid weeping past the seal.
Replaced the caliper, all working well now. Expensive way of finding the fault, but it may be your solution.

Does sounds like leaking piston seals.

Will be covered by warranty if it’s still under warranty cover.

Copper grease behind the pads.

The pads look like they have an uneven wear pattern – are you sure the brake is lined up perfectly? Just being slightly off will reduce power and cause noise.

Some muddy gritty water covering the disc and a few downhill drags should sort them out.

Have you aligned the calipers? Slightly loosen the mounting bolts, spin the wheel/apply the brake a few times, then hold the brake “on” whilst tightening the bolts back up.

Could try a new set of pads, after wiping the discs with white spirit or rubbing alcohol (IPA) (not India Pale Ale).

Alternatively go for a wet muddy ride, that normally sorts it out 🙂

Have you aligned the calipers? Slightly loosen the mounting bolts, spin the wheel/apply the brake a few times, then hold the brake “on” whilst tightening the bolts back up.

Yep, always do this but find it a little unreliable tbh. Typically one pad will always end up rubbing the disc, so end up doing it by eye instead.

Still, can’t understand why after testing 3 weeks ago all was good, and now no power and squealing brakes. Makes no sense.

The proper way to align the calliper is to take the pads out and space the gap evenly with the disc. If you have the dished washers then you need to take extra care to get lined up.

The disc could be slightly out of true. You can judge this by spinning the wheel and looking for a buckle where the disc moves side to side. An adjustable spanner screwed up tight to the centre arms of the disc will allow you to bend major kinks out and on the disc to fine tune. Bend the opposite way to the buckle deviation direction, if disc bends right from the centre line bend left.

I used to build bikes and almost all of the disc brakes needed this fine tuning.

Swap the front and rear disc if they are the same size, as an experiment.

Are the forks QR or screw axle? Fork sag and action, properly balancing each leg could help sort flex.

If you are based near London I would be happy to have a go at sorting them.

By the time you’ve faffed around buying pads, more fluid etc, the £35 for a new one (from bike-discount) will seem like money well spent.

Running out of ideas here.

In summary:

They were squealing and had no power..
I cleaned the rotors and the pads fearing contamination.
I bed the brakes in and the squealing went away and the power came back.
Two weeks later after not using the bike the squealing and lack of power are back.
I’ve checked for a leaky piston, but can’t find any evidence that it’s leaking.
Checked and double checked the pad alignment, all is good.
This is happening on both the front and rear brakes.

Grrrrr.

Oh well, got some new pads on the way and a big bottle of IPA to cleaner the rotors. If this doesn’t work I see it being new brake time…

Dumb question…..you dont store it upside down do you? Not ideal for hydro brakes.

What do you wash your bike with? I have stopped using any detergent near the brakes as I am sure this can kill pads on it’s own if left on there for a while. I have tried oven bake, boil wash, scrape/rub/file to recover the pads with little success; No substitute for new pads if you have got something in your old ones

If problem comes back, you may well have a leak of course…

Dumb question…..you dont store it upside down do you? Not ideal for hydro brakes.

Nope.

What do you wash your bike with? I have stopped using any detergent near the brakes as I am sure this can kill pads on it’s own if left on there for a while. I have tried oven bake, boil wash, scrape/rub/file to recover the pads with little success; No substitute for new pads if you have got something in your old ones

If problem comes back, you may well have a leak of course…

I use Fenwicks FS-1 bike cleaner.

Take the pads out, squirt some water around the pistons, put something between the pistons to space them, and pump the lever. If the piston seals are leaking, you will see small bubbles around the seal. Another sign of leaking piston seals is always having small bubbles come into the reservoir when bleeding, even though the lever feels firm.

I’ve now had leaky piston seals on 3 different calipers I’ve used (M755, M775, M975).

Take the pads out, squirt some water around the pistons, put something between the pistons to space them, and pump the lever. If the piston seals are leaking, you will see small bubbles around the seal. Another sign of leaking piston seals is always having small bubbles come into the reservoir when bleeding, even though the lever feels firm.

I’ve now had leaky piston seals on 3 different calipers I’ve used (M755, M775, M975).

Thanks mate, I’ll try that tomorrow.

Possibly better to just use mineral brake fluid, not water, less risk of contaminating the fluid in the lines with water.

ON your second ride when you noticed the brake were rubbish again, did you notice if the lever felt soft and needed pumping up?

If so this is a sign that air is getting into the system so something is leaking.

From reading about on the web I think a common problem with Shimano brakes are leaking at the seals. Give the calliper and pads a very very good clean and then reassemble. Give the brake a few hard presses. Reinspect the pads and callipers so you notice even the slightest amount fluid? If so, you have a leaking calliper. Try cleaning the pistons and see if that helps or failing that replace the calliper.

If the lever felt stiff and did not need pumping up then suggests you have contaminated your pads somehow. Did you clean your bike? might be using some no bike safe detergents? Do you use a aerosol type lubricant which could have sprayed onto your brakes?

I went through this with my SLX brakes for months and months, in the end replaced the calipers (with Deore as the new SLX werent compatible with the old levers), this finally solved it, weeping seals were the culprit. They’ve been fine since. However I’m not convinced it wasnt in part caused or compounded by using brake and bike cleaning products to solve an initial problem, which then damaged/corroded the seals in some way.

oh yeah, it was diagnosed for me by removing pads, sticking some cardboard in the caliper, holding the lever half closed with a rubber band/toe strap whatever and coming back the next day to stained cardboard.

Invest in a proper brake system that you can service, like Hope.

I’m having the same issues with Shimano XTR M988’s, front and rear.
Bled last week, good power, good bite on a test run.
This week, spongy feel at levers and squeals.
Power’s still there but I really have to pull hard on the lever to come to a stop.
Can’t lock the wheels up at all.