What SRAM shifter do you have? That would help for sure. Some grip shifts are Shimano compatible and they would work wiht both Road and MTB rear mechs from Shimano as well as some SRAM rear mechs as all of these are 2:1 ratio. Example - Attack Grip shifts http://www.sram.com/sram/mountain/pr...-twist-shifter

All SRAM X series grip shift are 1:1 ratio and will only work with SRAM 1:1 rear mechs ie. X.7 - X.9 etc.
http://www.sram.com/sram/mountain/technologies/311