RV Repair: pace arrow 1986 rear diff type, rear disc brakes, pace arrow

Question
we are servicing rear brakes 1986 pace arrow & tech was asking what diff it has,it has rear disc brakes & full float rear axles

Answer
He wants to know what size ring and pinion you have.  How strong of a rear axle you have, mainly.  My guess is this matters for what size brakes to get.  You can find that out by calling a good auto parts store, like NAPA.  In Michigan, you can call the Romulus NAPA and they deal with heavy truck parts.  Might be long distance but worth the call.  You can also try a truck stop in your area, if they repair trucks there.  These places should be able to tell you exactly what axle you have.