First question I have to ask is..., what kind of condition are the brakes in..?? Work good, work just OK, or like stepping on a plum, and hardly any braking..??
Almost sounds like the wheel cylinder may have leaked some brake fluid into the brake mechanism. Or, dust turned into semi solids crudding things up. If it's not letting it fully release, it may be rubbing enough to self engage the expanders. If by chance when you get it torn down, and need replacement parts, call here:
Remanufactured Transmissions, Torque Converters, Engines - Joseph Industries They had the best prices on parts I found. If you call, and order before 10:00 a.m., parts will be at your door, more than likely the next day.
I know it's a whole lot easier to work on the brakes with that fender removed, but not sure how hard it is to remove with that type cab.
You'll need to drop the oil level in the trans/rear end also. The lower bolts that hold the brake assy. on, are lower than the oil level, and the holes go clear through the housing.
Hopefully the seal behind the brake unit is still in good shape, and not leaking. If it needs replaced, most definitely PM me on that one... Not that bad of a job, but you need to slip that seal over the splines, which can ruin it. Got an easy simple solution for that. I can give step by step directions on that one...
Also, if you want to have a look at the brake system, go here:
Construction Equipment Products & Services | Case Construction You'll need to navigate your way through the parts section to find your model, but it will give a great exploded view of it, and part numbers.
Hopefully you've got an OEM repair manual coming. If it is, you will love it..!! Very good manuals with step by step instructions.
And as for the diff. lock... Do NOT engage it when spinning..!! It can cause some serious damage...
I will try and keep tabs on this thread, but if I happen to lose track, and you have any problems, be sure and PM me... I'll help you with what I know.