Well, I finally got around to pulling the compressor and rebuilding the unloader valves. That thing is a pain to get out, it weighs almost 100 lbs with that pump on the back and you have to climb back into the little access area on the curb side to get to it. Word of advice should anyone be contemplating doing this, the bolts in the back are very difficult to see (you will need a mirror on a stick) and get to and they are not all the same. Looking at the photo, the bolts at the 6, 8 & 10 positions are 15mm bolts and easy to get to, the one at 12 is a 15mm nut and in close quarters but accessible but the 15mm bolt at 2 is tough and requires a fairly long extension and the one at 4 surprises you and is an 8mm socket head bolt and the most difficult of the bunch.
Once out the actual job of rebuilding is very easy, just pull the plate from the top of the compressor,
remove the valve pistons, drop in the new ones and put it back together. I tested it with the rig I had built to check it in the first place
prior to reinstalling it and unlike before it held pressure. After installation the system came up to pressure near what it had usually maintained though not quiet there. I installed a gauge in the line between the wet tank and the governor
so that I could check the cutout on it. fired up the engine and the cutout was set at 115 so I adjusted the governor to between 125 and 130. Starting with the tanks at atmospheric pressure I reach cutout in about 11 minutes. I still have a leak somewhere but the bus builds and maintains pressure very well so it is once again derivable. Now I just have to chase down the last of the leaks. Here is the kit you need.
