hi everyone, i am new to forum so excuse me dont know to much about my old bobcat. the problem is its not moving back /forward , i changed the drive motors around but left side still will not move. i have been told that it is the hydrostatic pump , i have also been told that it is the hydraulic pump. thats why i am here, i have looked but i cannot find anything on the 643 bobcat. help would be gratefully appreciated, i live in qld australia. thankyou shreder.
Welcome to HEF shreder. :usa I'm not familiar with the 643 as I've never worked on one, but if it's anything like the 743 the engine and pumps are in-line with each other, not sideways like later models. If that's the case, the 743 has a very short universal joint coupler between engine flywheel and pump input shaft. They are know for either stripping the splines on the coupler or u-joint going south. I'd check that first.
hi Willie, thanks for your quick reply, i may have not mentioned that the bobcat drives on the rhs and not on the left. sorry for that but i dont know how to add that on my question. thanks again jim
I wish I could help more but I don't know anything about the 643. Does it have the engine sideways in the machine frame driving the pumps by some form of belt?
hi Willie, the pump is driven by the motor with a coupling not by belts its strait in line with the pump. there is 2 pumps in line 1 drives the rhs drive motor and the other drives the lh drive motor . the rear pump must drive the lhs as that is where the hoses go to , so im thinking it cant be the engine to pump coupling or the internal coupling that connects both pumps together and the front pump operates the rhs drive motor.and the rhs drive motor is working ok.and the rest of the machine is working ok.thanks jim
Ok, that sounds like the same arrangement as the 743, the engine is is a straight line with the pumps coupled with a u-joint coupling. Yes, you have two variable displacement pumps (hydrostat) for each drive, left and right drive. Piggyback on the drive pumps would be the work equipment pump, typically a gear pump that works the loader functions, lift arms, bucket tilt, and aux hyd functions. If the various loader functions work proper, then not a problem with the shaft coupled to the engine. So, if we conclude we don't have a problem with power delivery from engine, loader functions work, yet drive doesn't work proper, it's unlikely that both drive motors would crap out at the exact same time. But at the same time, it doesn't make logical sense that both drive pumps would crap out at the same time??? Again, I don't know this machine, just throwing some thoughts out there. It almost sounds like the charge pump (which is internal within the two drive pumps) is not feeding oil to the drive pumps. But take that with a grain of salt as I don't know this machine. Again, 643, maybe related to the 743. As I recall the 743 had Vickers variable displacement pumps for the drives, whereas the later Bobcat machines used the Sauer Danfoss VDP pumps. Again, I know so little about these machines that it makes advice almost irrelevant. But I do hope you find a solution to your problem.
hi Willie, its a vickers pump, it may be the charge pump, would that let one drive motor work and the other not. do they have a charge pump for each side. i have been trying to download some thing but no success. thanks shreder
Shredder, I am wondering if you ever figured out the problem with your machine. I am looking at a 643 that has the exact same problem; no drive on the left. So I am extremely curious what your problem was and what it took to fix it. Mike