Originally posted by UncaStuart
Turns out that with the amount of braking they had been doing, the disc brake had heated to the point where the hydraulic fluid expanded and actuated the brake independently. We had to wait by the side of the road for the brake to release after it had cooled. They said this had happened to them a few times before, in similarly severe conditions. I don't know if this is symptomatic of disc brakes or if they are a special case for some reason. In any event, I have been perfectly happy with using a drum brake for a drag these last five years.
A hydraulic disc on a Calfee? What type of disc system is it: A Formula?
I'll try not to rant here, but hydraulic disc brakes -- even open system models like the Magura Gustav M or Hope's Enduro/04DH -- are not designed to be used like a drag brake on tandems. Mechanical discs can be used as a replacement for a rim brake and/or both rim brakes but if you "need" a drag brake the only proven product is the Arai drum.
We have mechanical disc drag brakes on both of our road tandems but they are older models of a Hope brake that's no longer produced. The disc does an adequate job of srubbing off speed for unloaded racing tandems touring in very steep mountain areas but are prone to fade, rapid pad wear and rotor problems when used for heavy teams or loaded tandems, i.e., they're better than not having a drag brake for the most severe terrain but they are still not as good of a drag brake as the Arai.
Avid's BB road disc brake is becoming a very popular item on the high-end custom and go-fast tandems as a replacement for the rim brakes; some builders like Co-Motion are offering them as the OEM rear brake to be used in combination with a front rim brake. Todd Shusterman at daVinci tandems -- the same guy who pioneered the independent coasting system for tandems -- has been fitting his 26" road & off-road tandems (all his tandems use 26" wheels) with primary Avid BB brakes front & rear. Although he works closely with Avid whose business HQ is located just down the street from daVinci in Colorado, Avid will not officially state that it's disc brakes are suitable for use on tandems as a drag brake or as a primary brake. Glenn Erickson has also started to build road tandems with dual Avid brakes as OEM equipment.
While Co-Motion, daVinci & Erickson's use of the Avid's is best characterized as real world "Beta" testing, I believe these folks must have a high degree of confidence in what they've experienced in their own use of these brakes on their personal tandems before offering them to their customers. However, consumers must recognize that these are still not disc "drag brakes" and, instead, are a new form of primary brake that offers superior modulation and stopping power in dry & wet conditions and offer a method of preventing heat-induced tire/tube failures. Yes, they have their own unique failure modes, but none come to mind that are as potentially hazardous as tire blow-out caused by excessive rim heating.
Lastly, we can also speak to hydraulic brake performance as it pertains to off-road tandems. We have a F/S tandem fitted with Hope's Enduro 4 pot hydraulic discs -- an open reservoir system designed for downhill racers -- and also owned the previous model of 4 pot Hope hydaulic disc -- the DH04. These are great primary brakes for off-road tandem teams who venture onto single track, ride aggressively and/or who ride in wet or muddy conditions. However, as good as the hydraulic brakes are they are still not useable as drag brakes and if you overuse the rear brake to scrubb off downhill speed on long descents even the open reservoir models will eventually lock-up.
Disc brakes may never replace rim brakes entirely, but I suspect you'll continue to see them on more and more higher end road and off-road tandems. Make sure your dealer or builder knows how you intend to use your tandem if you think you'd like to use discs. Some applications are perfect for the discs whereas others are best met with the very reliable Arai drum brake.