New (to me) definition of brake fade?

[KaTooMer]

Saw this posted on a mountain bike forum:

"Brake fade isn't caused by boiling brake fluid, it's caused by the brake pads becoming extremly hot and giving off gases, these gases become traped between the pads and rotors when one tries to brake, keeping much of the pads from touching the rotors, this is why braking power is reduced."

Obviously the first part of this guy's comment is wrong, but I've never heard of trapped gases causing fade...a fancy way of describing glazing, maybe?

 

[WoodsRider]

Personally I think the guy has been sniffing too many gasses and is experiencing brain fade. :confused:

 

[KaTooMer]

Originally posted by WoodsRider
Personally I think the guy has been sniffing too many gasses and is experiencing brain fade.

Another guy replied "That's what I heard, too." Must be a moutain biker thing. :confused:

 

[marcusgunby]

Be carefull as this maybe true-i think the problem you write about is where the brake goes spongey and so doesnt work-the problem he is talking about is where the pads are getting too hot at the face.You still have a firm brake but no stopping power.

 

[jmics19067]

Yeah I tend to agree with brake fade has a lot more involved in it then just brake fluid boiling. Brake fade is a major problem with air brake equipped trucks going down long steep hills so boiling brake fluid has nothing to do with it .

My original thoughts with drum brakes fading was the drum expanding throwing off the leverage points and adjustments of the brake shoes but that doesnt explain why air operated disc brakes fade. There just may be more to this guy than hokeyness.

 

[WoodsRider]

Brake fade is usually caused by contamination of the pads/shoes (ever hit the brakes after driving through deep water?), contamination of the hydraulic brake fluid or glazed pads/shoes. I find it very difficult to believe gasses being given off by the pads/shoes are causing brake fade. Especially since gasses are compressible. :think:

 

[jmics19067]

brakes definately loose their effectiveness when they get hot. On an air brake system that takes the boiling brake fluid out of the equation. A truck can have good brakes before going down a long steep hill, lose braking effectiveness, and then have decent braking after they cooled off if the driver didn't burn them off or crack them.
I don't know why brakes can loose their coefficient of friction when super heated but perfectly good braking systems in dry weather can be rendered useless by heat between the shoe and drum or pad and disc. I have no proof or idea why it actually happens so I am not discounting the possibility of that statement . There is definately more to "brake fade" than just foriegn material or mechanical/hydraulic clamping pressure issues.

I am not discounting that the super heated drums and rotors are actually liquifying at the contact or that brake material just becomes useless after a certain tempature either, which are my actual true beliefs on what I consider brake fade. Talking runaway truck ramps and wheels on fire stuff here.

Now on my dirt bike I can be fairly certain to blame my lost braking effectiveness on foriegn material but I wouldn't use the term brake fade as I am speaking now.

 

[Yzag]

There are three kinds of brake fade from what I have read are:

1) When the brake fluid boils.
2) Pad fade. Friction will vary with temperature. As some of the friction material melts the pads hydroplane and will glaze the rotors.
3) Green fade. This is typical on new pads or pads that haven't been used hard. The pads have friction material embedded in a resin. When the brakes are applied hard the resin emits a gas. The pads then hydroplane on the gas.

I'm not sure about all of the details.

 

[tx246]

lots of mountain bikes that have disc brakes are not hydraulic but are actually mechanical disc. like air brakes, there is no system to get contaminated. that isolates the disc/pad as the point of the problem. when the pads/rotor get hot, there is a breakdown in the ability to provide friction. im sure there is somebody else here that knows more details.

 

[zippy1]

A disk brake will give off gas between it and the rotor when it gets hot. This gas makes a little cushion that prevents complete pad/rotor contact. That is why you see slotted and vented rotor's on performance applications. I am not sure how much gas would be produced on a mtn bike, but road goaing vehicles, Cars and street bikes, it is alot more than you think.