The brake calipers on these bikes are what is known as a "sliding caliper" i.e. the pistons in the brake caliper are only on one side - the back pad is passive. When you apply the brakes, the pistons are pushed out and this forces the inner brake pad against the inner side of the rotor. The caliper simultaneously slides inward on sliding pins, pulling the brake pad in the outer side of the caliper against the outer surface of the rotor. This system works fine - until the sliding pins seize up due to corrosion from road crud etc. Then the piston side does all the work leading to uneven pad and rotor wear and I suspect that this lies at the heart of the rotor problems some people on the board have been experiencing. This design was in use by the Japanese in the 1970's for god's sake...the only thing to commend it is that it's CHEAP. Other than that, a POS....
Most modern bikes have fixed caliper brakes with one, two or even three pistons in each side of the caliper (two, four or six pistons total). The pistons are said to be opposed - i.e. they work against each other. When you apply the brakes, all of the pistons force the brake pads against the rotor, and the caliper assembly does not have to move. True, these brakes can also suffer from stuck pistons but so do the sliding caliper type. IMHO, the stock brakes should be replaced with an opposed piston type. I beleive the Harrison billet calipers for the Thunderbird sport will fit our bikes and also there is an offering available via Triumph. Hope this helps
Jan
