sonikk4, I am referring specifically to unbranded ali calipers from aftermarket suppliers, and some that are branded, and rather expensive, but not made by a recognised brake system manufacturer, and not tested to a sufficient number of load cycles. Sorry if that was not obvious. Willwood are made to US standards, which are likely to be less stringent than what we usually see in the UK, but probably still acceptable, and of course genuine AP, Girling, etc will be ok.
However, it is a necessary consequence of using ali that such calipers have a finite fatigue life, unlike steel, whose fatigue life will be infinite, if properly designed. We don't know what design assumptions the manufacturers have made. The only guidance I have found on the number of brake cycles to be applied was for trailer towbars, where the testing is for 100 million cycles, and if that is applied to brakes, certainly copper pipes will fail, many times over, and I have severe doubts that an ali caliper will survive. But it all depends on the detail design, and those which have been modified to get wheel clearance are extremely vulnerable, as metal has been removed from the vital, highly stressed area. I assume that certain German vehicles, for example, have plenty of metal in the critical part of the caliper, so that the remainder of the vehicle is life expired long before the caliper reaches the end of its fatigue life, but that may turn out to be untrue. I am seriously expecting an outbreak of structural failure of ali space frames and suspension parts within the next 5 to 10 years, and it will in part be due to owners having managed to stress the cars beyond the assumptions made by the designers. It does not take much repetitive overstress to undermine the calculated fatigue life very seriously.
Basically, none of the manufacturers are telling us what we really need to know, in order to determine whether their products are safe in our proposed applications, and for how long. And that is what concerns me most. I did see someone, possibly Willwood, publish rated pressure, which is a start, indeed on a steel caliper, if the peak pressure remains below the fatigue threshold, that is the only bit of information that is really needed, but with ali it is not that simple, and some kind of graph or formula relating peak pressure to cycles before failure is the bare minimum that would be acceptable.
Edited by tiger99, 05 April 2014 - 01:10 AM.
