How to identify different types of brake fade?

[jonnyozero3]

Track duders and dudettes,

I had a friend cook a set of Wilwood brakes today (on a WRX) while I beat on my AP Racing set (it loved it), so it got me thinking about this topic.

If those more experienced could share their knowledge, it could be helpful to us novices. When different things happen on the track, there's so much (subtle) going on, that often it seems hard to recollect or know immediately what is really happening. For instance, when "brakes fade" or fail. Selfishly, I'd like to get some notes on what the different types of fade feel like, for future reference. I figure this discussion could be useful to a lot of folks new to track driving.

With that in mind, here's a starter. Who's got spears to chuck at this? Good reference links? Anyone want to add any thoughts? I know there has to be *a lot* more to add that can make us all smarter on brakes. Caveat: this is part Wikipedia, part bro-science, and part just me trying to explain things I've experienced.

TYPES OF BRAKE FADE:

1. Friction Fade
- Brake Pads reach "knee point", aka, overheat. Meaning, your pads are so hot, they lose effectiveness. Your pedal remains firm, but the stopping power gradually (sometimes quickly) is reduced.
- If the stopping power drops suddenly with a firm pedal, it could be "green fade". Meaning, new pads that have not fully bedded-in could suddenly vaporize some internal materials at high temperatures, resulting in an off-gas event that suddenly reduces braking ability
- Faded pads will return to normal effectiveness after cooling, unless "glazed" with a shiny appearance of melted material. This glazed coating should be scrubbed off (e.g., rub on asphalt).
- Note: may higher-temperature pads do not begin to provide high coefficients of friction (mu) / performance until they reach a specified operating temperature. They may feel weak or faded when (relatively) cold.

2. Fluid Fade
- Brake fluid boils. Your brake fluid exceeds it's current boiling point (that point in temperature reduces over time as the fluid absorbs moisture). Your pedal suddenly becomes "spongy", aka "pedal fade".
- Brake fluid has air bubbles. Your brake lines were not bled properly and there are bubbles of air within the system lines. Your pedal is spongy all the time, when the fluid is cold or warm.

Any other types of brake fade and failure we should know about?

Decent article for reference: http://www.torquecars.com/articles/brake-fade.php

[Midnight Cinderella]

Really wishing someone had replied to this thread right about now

[GrandSport]

I mean, brakes can fail in all kinds of ways, but if it's fade, it's probably your pad or fluid. As mentioned, fluid is when your foot goes to the ground but the car doesn't slow down (as much). Pad is when the pedal is firm but it doesn't slow down.
Air in the lines is different though. You always have a soft pedal that feels mushy- cold or hot. That's not really "fade." You can also have a bad master cylinder that can be confused for air in the lines. I think you pump the brakes with the car off and if your foot goes down, rather than it getting firm, it's a bad MC.

[ka-t_240]

Since they mention specifically Willwood in this case... One more thing to consider....

If they were the 4pot willwood/superlites there have been many cases of those calipers having major issues with caliper flex. I have seen it on a Miata and a SRT4 where the calipers flexed so much it created a soft pedal feel.

[ka-t_240]

Looks like GrandSport has the basics pretty well covered:

pad fail = Firm Pedal no stopping ability
boiled Fluid = Pedal seems fine, then it get soft and travel increases as you are on track.

[DarkPira7e]

Pedal does nothing = ruptured line

[ka-t_240]

Originally Posted by DarkPira7e

Pedal does nothing = ruptured line

That sounds like a much more serious issue than fade

[GrandSport]

Originally Posted by DarkPira7e

Pedal does nothing = ruptured line

depending on where it ruptured, car pulls hard AF to one side = ruptured line.
More than likely, a small leak will be "deceleration is dependent on acceleration of brake pedal and my brakes are on fire"

[dpaqu]

Originally Posted by GrandSport

depending on where it ruptured, car pulls hard AF to one side = ruptured line.
More than likely, a small leak will be "deceleration is dependent on acceleration of brake pedal and my brakes are on fire"

I thought the two MC circuits were on the front and the rear respectively. If you blow a hose you'll lose the front or the rear not the left or the right.