Editing Brake fade (section)

==Factors contributing to fade==
Brake fade failures can [[Cascading failure|cascade]]. For example, a typical 5-axle truck/trailer combination has 10 brakes. If one brake fades, brake load is transferred to the remaining 9 brakes, causing them to work harder, get hotter, and thus fade more. Where fade is non-uniform, fade may cause a vehicle to swerve. Because of this, heavy vehicles often use disproportionately weak brakes on steered wheels, which hurts the [[stopping distance]] and causes brakes on non-steered wheels to work harder, worsening fade. An advantage of low-fade brakes such as [[disc brakes]] is steered wheels can do more braking without causing brake steer.<ref name="ganaway">[http://www.dtic.mil/ndia/2002tactical/ganaway.pdf Gary Ganaway, Air Disc Brake Production, Use & Performance] {{Webarchive|url=https://web.archive.org/web/20110604041202/http://www.dtic.mil/ndia/2002tactical/ganaway.pdf |date=4 June 2011 }}, NDIA Tactical Wheeled Vehicles Conference, Monterey California, 28 January 2002. Accessed 2010/01.</ref>

Brake fade typically occurs during heavy or sustained braking. Many high-speed vehicles use disc brakes, and many European heavy vehicles use disc brakes.<ref name="ganaway"/> Many U.S. and third-world heavy vehicles use drum brakes due to their lower purchase price. On heavy vehicles, air drag is often small compared to the weight, so the brakes dissipate proportionally more energy than on a typical car or motorcycle. Thus, heavy vehicles often need to use [[compression release engine brake|engine compression braking]], and slow down so braking energy is dissipated over a longer interval. Recent studies have been performed in the United States to test the stopping distances of both drum brakes and disc brakes using a North American Standard called FMVSS-121.  The results showed that when newer compounding of friction materials typically used in disc brakes is applied to drum brakes that there is virtually no difference in stopping distance or brake fade.{{citation-needed|date=January 2022}}  As the United States changed its FMVSS-121 rules for Class Eight trucks built in 2012 to reduce stopping distances by about 1/3rd there was no recommendation to use either drum or disc brakes in the current law.

Newer drum technologies and turbine cooling devices inside of these drums has also eliminated any edge disc brakes may have had in heavy duty applications.  By installing brake turbines inside of a specially configured drum, temperatures are many times cut in half and brake fade is nearly eliminated.

Brake failure is also caused by brake drum [[thermal expansion]] in which brake shoe clearance becomes excessive from wear. This was largely remedied in the 1950s by [[Drum brake#History|self-adjusting brakes]].<ref name="Spartan">[http://digital.lib.msu.edu/collections/sesquicentennial/se/se-38.pdf?CFID=1834320&CFTOKEN=86763474 ''Spartan Engineering 1959'']{{dead link|date=November 2016 |bot=InternetArchiveBot |fix-attempted=yes }}; Disk Brakes; accessed 2007-02-26</ref> Maladjustment with wear is still a factor in trucks with drum air brakes.<ref name="Dana">http://www.roadranger.com/ecm/groups/public/@pub/@roadranger/documents/content/rr_axag-0300.pdf{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }}; Dana Spicer Trailer Axles & Brakes; Application Guide AXAG-0300 March 2006; See "Brake Fade" in glossary; accessed 2007-02-26</ref> A Canadian survey of randomly stopped heavy trucks found over 10% of trucks using self-adjusting brakes had at least one brake out of adjustment, due either to failure of the self-adjust mechanism or wear beyond the capacity of the self adjuster.  Newer brake pistons ("cans") extend stroke from about {{cvt|65|to|75|mm|in}}; since about {{cvt|30|mm|in}} of stroke is used just putting the pads in contact with the drum, the added {{cvt|10|mm|in|1}} of stroke is over 25% increase in useful stroke. Longer stroke reduces especially wear-related fade, but drum brakes are still fundamentally prone to fade when hot.

After cooling, faded brakes usually perform as well as before, with no visible change to the brake shoes and pads. However, if the brakes have been excessively hot for a prolonged period of time, glazing can occur on both of the friction linings of the shoes and pads.
When this happens, the contacting surfaces of the linings will have a smooth, shiny appearance, and will not perform as efficiently to slow the vehicle under braking.
This glazing can be easily removed by either gently using [[emery paper]] on them, or by driving the vehicle carefully whilst implementing light use of the brakes for several miles.

Long dual-tire [[skid mark]]s on highways, made by trucks with drum brakes, are visible examples of non-linearity between brake response and pedal pressure. Large trucks still use drum brakes because they are economical and fit easily where an equivalent disc brake does not. More recently disc brakes for trucks have been promoted listing features such as no fade, possible because they have no self-assist (self-servo).<ref>[http://www.roadranger.com/Roadranger/productssolutions/brakes/airdiscbrakes/index.htm Air Disc Brakes]</ref>