I have a friend who has an old Trek 800 series mountain bike (maybe from the '80's?) and it has a set of brake calipers on the rear wheel that are mounted under the chain-stay! Some of you have probably seen this brake design before but I never have. Does anyone have any information about this brake design? It seems a bit odd to me and my friend says that it's a pain in the neck when he rides through mud or snow - the caliper tends to collect the aforementioned like a beaver dam.