I inspected the brakes carefully on the pre-purchase. They looked like new and the owner said it got new rotors, pads, and a air/hydraulic unit just before he bought it. After 4 years I decided to check the brakes and flush the system. All four calipers had cracked boots. This can lead to the pistons getting seized from corrosion. I couldn't get new boots without buying caliper rebuild kits. They ran about $50 a wheel so it wasn't too bad.
The brakes were really easy to work on compared to a lot of light vehicles I've worked on. The retaining clip is held on by one bolt and drives out easily. The pads were still in good shape but new ones were pretty cheap so I replaced them while I had the calipers off. I did find that someone used brass fittings to connect the brake lines to the calipers. Not a good idea as they are pretty easy to bust off. There was also no way to remove the lines without rotating the whole caliper as there was no swivel fitting. Also leads to issues of not being able to properly torque the fitting. I believe this was the factory installation.
I had new brake lines made up at a local shop with the proper steel ends.
The Pistons popped right out with the air hose. Be sure to put a wooden block in to keep one from popping all the way out with no way to get the second one out as the chambers are interconnected. I don't learns fast but what I learns I remembers. Wear splash goggles as the propylene based brake fluid can cause permanent damage to your eyes.
The bores on the calipers looked like new which was a relief as the Meritor calipers run about $800 a piece and about 1/2 that for remans. Assembly takes a bit of a technique that you will master by the 4th caliper.
Total cost was about $500 including hoses and a gallon of Castrol Dot 3/4 to flush and fill the system. The job really wasn't PITA I expected.
Next write up will be on installation of a Pacbrake.