Bobcat 863 Drive Issue

[314raptor]

I need some help with an 863 drive issue. The machine starts up and operates fine for 3-10 minutes before it acts up. Then all of the sudden I loose drive. The machine will coast to a stop and I can't steer. Engine RPM's remain unaffected. I still have lift/tilt bucket control, but no drive. I can get the machine to temporarily work again in either of 2 ways. First, if I throttle back to idle, and tilt the bucket, drive comes back. It will work for a couple of seconds up to a couple of minutes before the problem recurs. Tilting the bucket doesn't fix it unless the throttle is at idle. The second way I get drive back is simply turning off the ignition and restarting. Once I hear the BICS click it works for a couple of seconds up to a couple of minutes then fails as described above. It seems to malfunction most often when I increase RPM's, but will fail even when operating continuously just off of idle. Hydraulic fluid is full. The drive belt is properly tensioned. My mobile mechanic has tried unsuccessfully to fix it. He has replaced some solenoid underneath, some relief valve, and the seat bar switch and magnet. He was sure it was fixed each time, but he apparently never test drove it long enough after each repair. Any tips would be greatly appreciated.

 

[bttpe]

Here's some basics you probably already know. Movement of the Bobcat needs the hydrostatic pump to work and for both hydraulic motors to work. Most mechanics want to test pressure and flow out of the pump to verify the pump. You can get a pressure gauge and fittings and put them inline to one of the motors and that should tell you if you are at least building pressure. (the lift and tilt have their own pump so they would work independently). If the pump has pressure we have to suspect the motors. It would be weird if they both failed at once. Usually only one is weak and the other still works. The motors have three hydraulic lines to them. Let's call them Forward, Reverse and the return line. The return line will have a filter inline with it. The return line is smaller. Why don't you check the filter in the return line. Might as well buy one and replace it to check. When you take the filter out see if it has metal filings in it. That might tell you if a motor is failed. I would also have you check the brake but it sounds like it will move a little so the brake should be off. Sometimes I just unbolt the brake when testing movement just so I'm not fighting the lap bar and seat switch. (Please don't leave it off it's your personal safety device). Let me know how checking pressure and the filter goes.