Avoiding overheating disk brakes.

[Thor Buttox]

My XT (M785) brakes have over 2 years and thousands of km on them. No bleeding or maintenance needed to date other than occasional new pads.

 

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Now that you mention it, The XT's on my old 26er also almost never needed it. They were bullet proof. So yes, I have two different XT sets with very different results.

[Thor Buttox]

How is the stopping power reduced? Do you find there is too much travel in the brake lever when you brake?

 

I have this problem on my formula one brakes. I remove the wheel, pump the brake lever a few times and the brake comes up again. Need to do this as the brake pads wear out. When I replace the pads I use a screw driver and push the old brake blocks apart again. The problem is that the brakes are not really self adjusting.

Exactly that. Pressuring the system by pumping the lever shows there's definitely air in the system. Problem is how quickly it is going from being perfect to needing a fix. The new shop I took it to says it needs to be 'bled under pressure'. Not quite sure what that means relative to the normal way the other shop did it, but we'll see. Like I said above, the old XT on my 26 didn't need it at all.

[Spoke101]

Ok, we might be onto something.  Bike is almost a year old.  Have done 1500 km of which most of it was in the last 3 months.  I have not done any maintenance on the brakes yet.

 

When you pulled the brakes did the levers pull all the way to the grips or was there resistance but just no stopping power?

[JXV]

I do beleive that this was an extreme case and think technique was more the issue in a extreme situation. Few lessons learnt but I am sure there are some things to take into consideration for the next time.

Stick to OE pads,rotors, fluids and hoses. Go to bigger discs if necessary. I'm 86kg and I run 203mm front and 180mm rear discs on a 29er. Rock reliable 1 finger braking.

 

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[Spoke101]

Exactly that. Pressuring the system by pumping the lever shows there's definitely air in the system. Problem is how quickly it is going from being perfect to needing a fix. The new shop I took it to says it needs to be 'bled under pressure'. Not quite sure what that means relative to the normal way the other shop did it, but we'll see. Like I said above, the old XT on my 26 didn't need it at all.

 

This is not always the case with Formula. They tend to have a large amount of lever travel for the related piston travel. Thus as the pad ware down the lever has more and more free stroke. It is not that there is air in the system or the brakes are not bled properly. I normally over fill the reservoir to solve this but then your brakes can pump up if they  left in the sun.

[Bateleur1]

When you pulled the brakes did the levers pull all the way to the grips or was there resistance but just no stopping power?

 

Soon after starting the final descent as I pulled it slowly pulled all the way to the grips and after that the stopping power gradually reduced.

[Spoke101]

Soon after starting the final descent as I pulled it slowly pulled all the way to the grips and after that the stopping power gradually reduced.

 

This is an indication of air in the system. As the mineral oil heat up the air bubbles make there way up to the lever and then when you pull the lever the master cylinder is trying to compress air as there is no more fluid in the reservoir to be pushed down to the caliper.

 

Easy to fix by topping up the fluid and removing the air if you know what you doing, otherwise you can bleed the brake but this is a far bigger job but might be better as you might have cooked the mineral oil (ie: it's turned black).

[Spoke101]

Braking technique is also important. You don't want to drag your brakes (ie: constantly have light pressure on the levers) as this builds up heat in the braking system. Rather have shorter sharper brake periods and then release the brakes. This will also prevent the rotors and pads from glazing and keep brake performance up.

 

You will also have more grip when cornering if you do most of your braking in a straight line before you get to a corner and only maintain speed through the corner with the brakes as (in simple terms) the tyres have one less force acting on them. This increases traction and therefor you can corner sharper and faster. It does take some getting used to, mainly the judging of how much speed to scrub be fore turning into the corner (this is a lot easier on trails where you know whats coming vs new first time stuff).

[Headshot]

Soon after starting the final descent as I pulled it slowly pulled all the way to the grips and after that the stopping power gradually reduced.

If you are located in Germany does this mean you were riding  an Alpine trail in Europe? If you are doing big descents like that regularly you probably need to upgrade to bigger brakes and maybe even a trail oriented bike. 

 

I run 200mm front and 180mm at the back with SLX brakes. I have never had an overheating situation as you describe despite infrequent maintenance and using the brakes a bit on very long alpine descents last year. I am 1.88 and 87kg. 

 

Bigger rotors make a huge difference and that's probably your cheapest solution, along with a brake bleed. 

[JXV]

Now that you mention it, The XT's on my old 26er also almost never needed it. They were bullet proof. So yes, I have two different XT sets with very different results.

I'm convinced that a lot of braking issues arise from 4 things that manufacturers cannot properly control at the factory. These are :

 

1) shortening of hydraulic hoses at time of fitting. This is when air gets into a factory bled system and ongoing problems result from incorrect jointing by the person who shortens the hose.

 

2) maintenance shortcuts taken by LBS mechies who are frequently not formally trained - I've watched many of these guys in action and many of the problems stem from time pressure.

 

3) Alignment and facing of caliper mounts - there is often misalignment between your post mount and the plane of disc rotation. Not all LBS will use a post mount facing tool when they assemble your bike. Just the thickness of paint can be a problem. I have also found mounting washers that were not flat so the alignment shifts as you nip up the mounting bolts. If the pads are not exactly aligned to the face of the disc your brakes will never be quite as good as they could be.

 

4) Height of caliper relative to disc. If your pads sit too far out or too far in on your discs then you lose braking surface but also, the brake disc and pads wear faster on the inner or outer edges so that eventually the disc faces are no longer parallel ...every new set of pads you fit after that will wear unevenly and take longer to bed in.

 

 

 

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[JXV]

Soon after starting the final descent as I pulled it slowly pulled all the way to the grips and after that the stopping power gradually reduced.

If you pull on the brake lever and it goes hard but slowly sinks to the bar with sustained pressure then the main seal is leaking. This means the system cannot sustain the pressure you are applying

 

If you pull on the lever and it feels spongy then you have air bubbles being compressed under pressure. This means the pressure you apply can be sustained but some of your energy is used to compress air and only the remainder is available for braking. As it heats up the air expands and the effect gets worse.

 

Then there is brake fade - this is normally taken to mean that the braking material loses friction as it gets too hot. It can also occur if the brake fluid gets so hot that it boils (or water contaminating the fluid starts to boil). MTB brakes seldom get this hot......

 

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[lerouc]

I had avids that overheated. Changed to SLX brakes, upgraded both rotors to 180mm XT ice-tech rotors. Still using non-finned pads but have not had an issue since.

[Bateleur1]

Braking technique is also important. You don't want to drag your brakes (ie: constantly have light pressure on the levers) as this builds up heat in the braking system. Rather have shorter sharper brake periods and then release the brakes. This will also prevent the rotors and pads from glazing and keep brake performance up.

 

You will also have more grip when cornering if you do most of your braking in a straight line before you get to a corner and only maintain speed through the corner with the brakes as (in simple terms) the tyres have one less force acting on them. This increases traction and therefor you can corner sharper and faster. It does take some getting used to, mainly the judging of how much speed to scrub be fore turning into the corner (this is a lot easier on trails where you know whats coming vs new first time stuff).

 

Here is a some of the Strava info.  Notice on the right of the profile graph.  I have positioned the cursos on the exact point where I had the brake failure.  It was very steep and the end of quite a winding road.  I quess the brakes were heating up and on the final descent it was just getting too much.  Notice the gradient (if Strava is to be trusted).  I was very very steep.

 

[Bateleur1]

If you are located in Germany does this mean you were riding  an Alpine trail in Europe? If you are doing big descents like that regularly you probably need to upgrade to bigger brakes and maybe even a trail oriented bike. 

 

I run 200mm front and 180mm at the back with SLX brakes. I have never had an overheating situation as you describe despite infrequent maintenance and using the brakes a bit on very long alpine descents last year. I am 1.88 and 87kg. 

 

Bigger rotors make a huge difference and that's probably your cheapest solution, along with a brake bleed. 

 

Was my first real Alpine trail.  Did one other but the road was not such a drop.

[gummibear]

180mm Icetech discs

 

Sintered pads

[Spoke101]

Here is a some of the Strava info.  Notice on the right of the profile graph.  I have positioned the cursos on the exact point where I had the brake failure.  It was very steep and the end of quite a winding road.  I quess the brakes were heating up and on the final descent it was just getting too much.  Notice the gradient (if Strava is to be trusted).  I was very very steep.

 

Unbenannt.jpg

 

That's a 1:1 slope ratio so yes it is properly steep.

 

Bleed brakes and upgrade to bigger rotors