A little while ago immediately after having my bike serviced my front brake started to squeal on every application, light or heavy. Bite and power was also out the window.

I assumed that during the service contamination had occurred of either pad or disc, so replaced both for an easy life – the disc like for like Shimano and the pads from Uberbike (original was Shimano OE). After bedding in all was fine and strong brake performance was resumed.

A couple of weeks later and the squeal is back, again with power and bite gone. I’m really confused! Can anyone shed any light as to what might be going on?

The bike is my commuter, so used five days an week and the rear brake has remained fine throughout. There’s no obvious difference in the feel at the lever end so I’m assuming I’m not losing fluid, but could it be that?

The brakes are Shimano Deore M615 with basic Shimano discs. Any ideas?

Check for a leaking brake hose or piston. Could be brake fluid getting onto the brakes

Either there’s a leak at the calliper and the oil is contaminating the pads or something about your bike maintenance routine is contaminating them would be my guess.

Happened to me a couple of years back on a xt 785 rear brake. Fluid was leaking from where the hose connects to the calliper and running onto the pads. Luckily a warranty job for me

I’ve had a look at the calliper with the pads out and can’t see any immediate evidence of fluid anywhere. Am I best off investigating after a ride? Are there any tell tales that I should look for on the pads themselves?

I don’t think it’s maintenance – we had a bit of a dry spell and the bike hadn’t been washed from the time the new pads and disc went on to the time the problem reoccurred.

catch the light on the disc. If you can cause a smear on the braking surface with a clean bit of tissue, then it’s contaminated.

put the pads over some sort of heat source – bunsen burner or a gas hob, they’ll start smoking for a bit and then stop. I usually heat them for about 4 mins. Don’t burn the pad material, just heat them from below. Allow them to cool down naturally, pop them back in and your braking power will be restored!

“pop them back in and your braking power will be restored!”

maybe for a ride.

look at the caliper with a torch – squeeze and hold the lever

odds on youll see bubbling round the piston.

Your seals are starting to weap.

the time between squeeling brakes will get shorter and shorter the more you use em.

The carwash stuff i use causes mine to squeel like a piggy

Just clean the disc with clear nail varnish remover,

Or vodka

Commuting in traffic?

Mine used to do this regularly. I assume it’s simply contamination off the road. I used to do a wee diversion once every couple of weeks down a steep long road, get up some speed and brake while still pedalling. The heat would burn off any crap and normal service was resume for another two weeks or so.

This is a VERY COMMON occurence with shimano calipers.
This is not just confined to 1 particular caliper/brake, but across the full range
The problem is microscopic amounts of brake fluid seep/escape through the piston seals.
There are no user/dealer servicable parts i.e, no way of ordering replacement seals.
You should replace the whole caliper, which comes with new pads/bolts.
Be very careful when cleaning the brake disc as it is VERY difficult removing all contaminants of oil from it.

I work in a LBS, and between our hire fleet/customer bikes, we must have returned over 100 contaminated shimano calipers over the past couple of years.

Mine are BB7s.

Oh and I work in a LBS and I’ve never had to return any Shimano calipers.

Good for you, wish I worked there an all, then I would’nt have to bleed the darn things ever again.

Never had bother with leaking shimano calipers on my Devore brakes. Includes going from top of Deuxs Alpes then down to Venosc. They are 7 years old and are used throughout winter too.

Maybe as you commute, you are getting diesel on the front disc. Try cleaning with acetone or carb cleaner, on the disc.

Good luck with the fix.

Interesting. I have exactly the same with my front m785 too. I’ve changed pads (uberbike orange) and cleaned everything with alcohol, but the bite goes again very quickly and it’s so loud it could wake the dead.

Will take it off the bike and check for leaks.

I knew I should have bought Hopes! I have the previous gen xt brakes on my soda though and they’ve never missed a beat!

trail_rat – Member
“pop them back in and your braking power will be restored!”
maybe for a ride.
look at the caliper with a torch – squeeze and hold the lever
odds on youll see bubbling round the piston.
Your seals are starting to weap.
the time between squeeling brakes will get shorter and shorter the more you use em.

steffybhoy – Member
This is a VERY COMMON occurence with shimano calipers.
This is not just confined to 1 particular caliper/brake, but across the full range
The problem is microscopic amounts of brake fluid seep/escape through the piston seals.
There are no user/dealer servicable parts i.e, no way of ordering replacement seals.
You should replace the whole caliper, which comes with new pads/bolts.
Be very careful when cleaning the brake disc as it is VERY difficult removing all contaminants of oil from it.

I work in a LBS, and between our hire fleet/customer bikes, we must have returned over 100 contaminated shimano calipers over the past couple of years.

Thanks gents, you were both right. Time to order a new calliper.

Where did you find the best place to buy one from?

I had the same problem, but the oil was visible rather than microscopic, which made it an easier fix!

Contaminated brakes will usually give out a horrible juddering squeak as you roll to a halt.