Can anyone explain brake differences on these trucks?
 

I'm mixing and matching brake components between a 1987 squarebody and a 2001-ish gmt800. Both trucks are 3/4 tons. I've been trying to figure out what diameter pistons are used on the front calipers of a 2001. RockAuto is showing 57+57 and 40+44 calipers. I've seen some evidence of a 48+48 caliper as well. The vast majority of the available calipers are the 57+57 mm size.

When are the different caliper sizes used? Are they accompanied by a change in the master cylinder size?

Re: Can anyone explain brake differences on these trucks?
 

I will make an educated guess and say if you have the hydroboost setup, then you would get the bigger piston due to higher brake pressure. Most 2500/3500 came with hydroboost, while 1500s were your traditional vacuum booster setup.

Re: Can anyone explain brake differences on these trucks?
 

On 88-98's, caliper was dicatated by GVW.
1/2tons used the same caliper as low GVW 3/4ton.
Heavy GVW 3/4ton and low GVW 1tons used the same caliper with larger piston then the 1/2tons.
And then you had the heavy 1ton gvw which used a specific caliper I don't know anything about since I can't use it on my 1/2ton lol.