well im having similar problem on a komatsu d20 but as far as I know their power train is almost exactly the same except a bit bigger, first thing is i would check is take off the bolts to the cover on the sprocket and there is a big black nut i would see if it is loose posibly the sprocket is spining on the shaft that would be the worst case senerio but one of the easist to check, make a mark with a flet tip maker and then drive it a few feet and see if it has moved if it hasnt then great , the next thing is possible your linkage has gotten stuck on that side and is not releaseing the pin that sends oil to the hydraulic cyclinder to push your yoke arm in to disenguage power to your clutches just take seat off then plate and look at linkage and pull on arms and see if things are working like the other side, if good but possible your brake linkage is stuck but that would bog the engine down so that cant be it. the next thing is a real pain in the a hole , next i check and see what the oil looks like in that final drive see how much glitter if any is in the oil hopefully there is no chunks. if just dirty then your going to have to pull the clutch cover off that side its heavy and a pain, take picture of your linkage and so you know the extact lenght everything was when taking it apart. ok take cover off now your going to see a drum and a brake band on it, next to it will be a arm that gets pushed into the clutch pack in that drum. now if the arm is rock hard and wont move then the bearing might have or has broken and its frozen the arm pushing in the clutch pack but if it moves back and forth nice and smooth then another pain in a hole job is that your clutches are worn out which would be the best senerio and you have to unbolt the drum for both sides and lift it out, best to get some heavy duty zip ties and tighten brake band with 2 of them and then a set of come alongs to lift out unless you got some seirous guns on you its going to weigh about 85 to 90lbs my guess, now the flange that is closes to the drive sprocket there is a cover on a bolt take cover off and make sure bolt is tight hasnt moved or nothing if its loose then the pinion gear and flange most likely will have to be replace, now another issue that the bolts on the flange that is attached to the drum might have came out and the main shaft from the center of dozer is spining but now its not connected to drum so now power that you would be able to see as soon as you take off clutch cover thats a still a pain if that happend due the the threads might have got messed up and you have to change drum depending what side bolts broke from... I know this alot to absorb so any questions just ask away
