Shimano M446 Hell.

JayKay3000

I got a job in Essex, England and left my mountain bike at my parents while I sorted out space for it to come down later.
I went back home 3 months later and the Shimano M446 brakes did not work on my 2014 Giant Trance x2 27.5 mountain bike.

Bear with this wall of text. It might be hard to follow.

Before I left the brakes were working fine. I'd taken the bike on many rides and they just did their thing.

When I came back some months later I felt like I had ice for brakes. Full lever did nothing.

After a lot of cleaning of pads and disks I got the front to work and found a big hill to really get them toasty.

This process seemed to work and the front stopped on a dime.

I must have left the bike for a few weeks and came back to find the rear was not working.

I took it to the shop. They didn't seem to have a clue (giant reatailer by the way).

However, they did mention that these brakes or at least models of that year number were having problems. Lots of customers coming in with the similar problem on similar models of callipers. THANKS!

So they stuck some new pads in and it seemed to work at the shop.

I left the bike for a few more months and came back to find the rear not working. Full lever, squeal like a :roll: and refuse to do any locking on the tar mind.

I'm in the process of fitting a new seat and cassette, maybe a new chain and getting the bike ready for sale since my lifestyle means I need a less dedicated toy.

What with the horrible fox evo forks and the m446s doing this I'm wary of throwing money at the lbs and don't really want to sell the bike with this fault.

Should I get a new disk. Try isopropyl alcohol again or use some dedicated brake cleaner? Throw the new pads away ( did bed them in) or give the calliper a good clean with bike friendly brake cleaner?

Cheapest method really as I don't want to sink much more money into this bike. I can't imagine anyone would want to buy it if it only has front brakes.

Thanks!

The Rookie

Sounds like the pads were getting contaminated by something' that's usually the only reason the lever feels normal and yet you get no braking, cleaning them can work, but if the contaminant got deep into the pad it can just come out back to the surface again.

carvedmarble

I've had something similar with my rear caliper too, the specs say m445 but the caliper says m447 on it and the same thing is happening to my back brake. I use it daily to commute, have only ever used brake cleaner or ipa when cleaning the brakes and remove the wheel when doing anything that could contaminate them with lube, etc.

There are no fluid leaks on the caliper anywhere but with new pads its ok for a day or so and even with new pads and rotor the lack of braking goes away for a few days then returns, its so annoying. Must be a common problem with them. I'll be upgrading to slx when I get the money but until then the only solution i have found is giving the pads a cheeky roast over an open flame and a bit of a sand every 2 weeks and that seems to keeping it mostly at bay for now.

swod1

Carvedmarble, sounds like the pads are glazing on your rear brake.

Are you using resin pads?

carvedmarble

Yeah, B01S resin pads. I've no idea how to stop them glazing. I don't use that much rear brake to be honest. I mainly use the hike for commuting and a weekend play every now and then. I've never had the problem with the front brake.

Mister_g

I had something similar with my rear brake (M395). Everytime I left the bike for more than a few days the brake lost power, but after a bit of hard use it was OK. Then it got to the stage where it squealed like a pig and never regained its power until I changed the pads, then it was fine again for a few weeks. There were no signs of leaks.

When same thing happened with new pads I tried heating them on the gas stove to see if it helped. When I heated the inner pad, it was obvious that there was something in it, as something was bubbling and hissing on the surface of the pad. (I was using semi-metallic pads, btw.)

I still couldn't see any sign of a leak on the caliper, but I got it scrupulously clean, put the block in, and wrapped a bungy cord around the brake lever to pressurise it. After an hour, or so, there were still no drips, or anything, but I could see that on one side the small gap between the caliper and the piston had filled with fluid. This was only a tiny leak, nowhere near enough fluid to make a drop, but it must have been enough to slowly contaminate the brake pads.

It was the excuse I needed to buy some SLX.

JayKay3000

Hi Folks.

Update:

In an attempt to cure this issue and not go back to my lbs I decided to put chain cleaner onto the rotor (muc-off) and then sprayed it into the pads then used a toothbrush to clean both sides of the rotor.

Naturally the brakes went to ice and had no effect.

Fix:

Now with an even worse rear brake than before find the steepest trail and go as fast as possible remembering to use your rear brake hard to heat the rotor and pads.

Use steep terrifying descents (not necessarily gnarly) for this as you've got no hope in stopping mid-trail anyway so you're forced to use brakes.

By the end of the trail your brake will be locking up easily.

(if you end up in a tree... ...yeah...)

Overview:

I'm guessing the act of just getting the rotor and pads really hot is what burnt off any grease rather than the chain cleaner. I expect chain cleaner was better than using a lubricant like wd-40!

Now to go to bike park wales to do some fast blues to get my eye in again as I've not trail ridden almost all year!

The Rookie

Bike pads don't really get hot enough to burn the contaminant off completely, be prepared for the issue to come back as the contaminant comes back out from deeper in the pad.

step83

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19699777#p19699777]The Rookie[/url] wrote:

Bike pads don't really get hot enough to burn the contaminant off completely, be prepared for the issue to come back as the contaminant comes back out from deeper in the pad.

Seen this on a friends bike he did similar sprayed them with alcohol lit them (smart cookie he is) worked well for a few days then started squealing and not stopping. Ended up just getting a new set of pads.
Once a containment is in the pad it is very hard to remove. I would go with either sintered of Kevlar replacements neither are immune to contamination but they both should give you better braking.

The Rookie

I've had some success by soaking in petrol for 24 hours and then baking in the oven on max for about an hour, I then keep them in case of emergency (worn out pads and no new ones!)