Trying to mount a Hayes HMX-1 mexhanical disc brake on my GT I-drive. The caliper bottoms out on the rotor (6")and I still need about 1/2" before the mounting holes line up- so I need some kind of adaptor shim and longer bolts- the holes on the caliper are 54 mm as are my frame mount holes- LBS guy shrugs his shoulders and I can't find anything in the catelogs- can anyone tell me what I need and where to get it - online.