anyway to tell if i have 1" or 1.75" rear piston bores on 99merc w rear dsk
 

It looks like the 99merc i have been trying to get running while 100 miles away will need brakes on all 4corners before it will pass inspection (no wear sensor noise but brake light on the dash is lit). i see rockauto has a very good selection of pads but it seems there are two part#s and one factor is rear inboard caliper piston diameter for the retainer spring. Is there anyway to know which size it has without pulling the wheel/caliper?

Sometimes if you provide the complete vin# to the dealer parts dept they may be able to tell you which calipers the vehicle had when built.

thanks- i just pulled the wheels last night and had a look. it uses the larger ones. Found a nice package deal on ebay for 150$shipped, but it uses the smaller rear piston. The backs didnt look that bad anyway. I will probably just do the front and see if the light goes out (already checked the brake fluild level in the resv)

If the reservoir got too low, it may have picked up air in the lines. Be sure to do a fluid exchange to clear all air bubbles. Run fluid through each cylinder until it comes out clear and clean, starting at the passenger rearm then driver rear, then passenger front, and finally driver front. You will exchanging all the old fluid out.