I'm wondering what they did to get it out of diff lock. Normally the diff lock should release once you take the load off of the rear axle/ring and pinion. If your rear is loading up that solid, it makes me wonder what the runout is between the front wheels and back wheels. Post your tire sizes and what type. Maybe they put the wrong combo on your unit. Double check your tire pressures. Even still, you said you lifted the front end to try to break lock, right? Shoot, that may as well be the same thing as pulling it out of 4wd (runout problem or not). In case your wondering, the drive wheel tends to be the one with the least amount of weight on it, try an experiment, lift the rear off the ground (2 wheel drive only) and unlatch your brake pedals. With the wheels moving in either direction, tap the brake corresponding to either wheel, does it stop while the other keeps moving? If it does then the diff is working properly. With the diff lock engaged do the same
( just hold one brake) does it drag the engine down with increased whine from the trans? If it does then that's normal also. Now release the diff lock and repeat the first check, one wheel should stop while the other keeps moving. If the diff sticks again, gently move the pedal from forward to reverse and that should definitely break diff lock. If it does'nt, then there is a problem. As far as I know I've never seen a tractor with "limited slip" so that should not be a factor. If the tractor weight is fairly evenly distributed you will see tire spin from both wheels in a slippage situation. But if the diff lock stays engaged you will notice the nead for increased power when turning and if you are on solid ground where traction is good, you can't miss the fact that the diff is still locked. Your machine has a pinion gear that drives the ring gear, the ring gear is attached to a carrier assy that houses 4 diff gears. Without diff lock engaged the wheel that recieves the highest load will cause the diff gears to walk around each other and drive the opposite wheel. This makes it possible to make a smooth turn, being that the inside wheel does'nt have to travel as far as the outside wheel. With the diff lock engaged it basically "locks" up the diff gears so they can't walk around each other and both wheels will drive at the same time by engaging either a set of pins or somewhat of a cam lock to lock the opposite side of the diff gears to the carrier that the ring gear is fixed to. Kind of difficult to explain with just words but maybe that will help.
