MAINTENANCE OF HAT & ROTOR ASSEMBLIES USED IN HIGH SALT ENVIRONMENTS
Inspection and Maintenance of Hat & Rotor Assemblies in Severe Weather Conditions Where Road Salt is Used
Most high end performance brake upgrades historically have been used on cars typically not driven in harsh environments. With the advent of sports performance 4-wheel drive vehicles, brake kits are now more often used under severely corrosive conditions. StopTech 2-piece floating hat and rotor assemblies are designed for performance track use and in most circumstances can also be used without any special considerations on the street. While there are some original equipment 2-piece hat & rotor systems, none are of a floating design intended for competition. Routine maintenance is required for floating brake systems if they are to be exposed to salt. Regular maintenance will significantly lessen the chances of salt related corrosion problems, while in some cases, switching to the stock brakes for the winter may be the best option.
Why "Floating" Rotors?
All metals "grow" when heated. The diameter of gray iron brake discs can increase as much as 2mm (0.080 inch) at elevated braking temperatures. When the disc is radially restrained from growing (as in all one-piece discs or solidly bolted 2-piece assemblies) the friction plates are forced into a cone shape as temperature increases, adversely effecting both temperature and pressure distribution within the pads and the feel of the pedal. The StopTech racing and high performance street discs are mounted on separate billet aluminum hats or bells. The fastening system is designed to allow radial growth and minimal axial float resulting in a mechanically stable system. The images below show details of the hat, drive pins and rotor.
StopTech Floating Rotor System
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The ability of the system to “float” is compromised by severe
salt conditions as the open areas of the slots in the rotor become filled
with corrosion by-products (Fig. 5 & Fig 6). Driving in severe weather
where salt is used on the roads can also lead to corrosion and cracking
of the hats due to a galvanic couple between the dissimilar metals of
the Aluminum hat and iron rotor. This type of corrosion only occurs in
the presence of salt deposits and water (Fig. 7). In severe conditions
where salt is allowed to build up over long periods of time without cleaning,
electron flow between the hat and rotor can weaken the structure of the
aluminum hat along grain boundaries causing pre-mature cracking, termed
corrosive exfoliation. Brake systems driven in severe weather conditions
should be cleaned during the winter as often as practical, particularly
on the inside of the rotor where salt and corrosion can build up. Annual
inspection after winter is also recommended for early detection of any
pre-mature cracking. Salt will also attack the hard anodized finish on
the rotor hat if allowed to stay in contact without periodic cleaning.
Flushing the rotor vanes with fresh water as often as practical after
exposure to salt will significantly reduce corrosion build-up in salted
environments. After winter and before taking the car onto an open track,
excessive corrosion inside the rotor should be cleaned as best as possible
for optimal cooling performance.
Corrosion Effects
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Stoptech offers a zinc coating (Figures 8-10) for their Aerorotors®
to provide a sacrificial coating for its customers that reside in severe
weather environments. This coating provides corrosion protection without
the pad and rotor friction bed-in compromises and environmental impact
of other coatings.
In the near future, Cadmium, Zinc, and some other heavy metal coatings,
will not be allowed in Europe or the United States so we are working on
coatings like GEOMET® to replace the zinc-coating that we currently
offer.
We do not recommend Zinc or GEOMET® be used on a dedicated racing application or in non-severe weather environments.
Strict adherence to StopTech’s bed-in procedures is required to maintain the functionality of the coating.
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