howdy to all. well I had been fighting a bear of a problem on my Kubota L355ss and finally found the problem, and the fix was simple (and practically free) so I thought I'd share it here so if other folks have the same problem they might be able to fix their tractor.
the problem was: my L355ss had a slipping trans- especially in the higher gear ranges, the problem was the same in forward or reverse. i built a pressure guage using an inexpensive guage that reads up to 500 psi and had an adapter hose made to connect it to the 1/8"npt pressure fittings found just below the direction selector valve on the shuttle shift valve. I performed a pressure test of the shuttle valve and found that at idle the pressure on the forward/reverse circuits was barely 50 psi, and at high rpm it was barely 100 psi, spec is 230-255 psi. after messing with the shims for the shuttle pressure regulator i managed to get the pressure up to 75 psi idle and 150 psi at high rpm. still not enough. i looked elsewhere for the pressure problem. i found that the pressure has to go from the pump to the three point lift first before going to the shuttle valve. at the left hand side of the three point control system (below the seat just below the seat bracket is a valve setup with a pipe on it that feeds the shuttle valve. this valve is called the "Flow Priority Valve". in essence it allows two hydraulic systems to use the same pump- in this case the shuttle system and the three point. i took it apart and found that the plunger (part #4 on the attached picture) was stuck in the bore of the valve body. i removed all three plugs (one on top and two others one just above the feed pipe to the shuttle valve (#6) and one on the back side (that is #5) on the diagram. i had to tap the control plunger out using a dowel (it should slide smoothly). to repair the plunger i mounted it hand tight in my drill press and used emery cloth to polish it to the correct size. this will take some time as i would do it a little at a time till it was just right- patience here is a must. when it fit 'just nice' i re-assembled everything and re-checked my pressures. now at idle i have 280 psi and it holds steady at 280 all the way through the rpms. i was able to take the tractor off and in 2wd mode i can now burn out in 4th gear!!
so I'd say its fixed. hope this helps someone not think their tractor is junk.
in the end I'd say check that plunger in the flow control valve first, and if its stuck like mine was, fix that BEFORE tearing into the shuttle system. it needs to slide back and forth easily.
the problem was: my L355ss had a slipping trans- especially in the higher gear ranges, the problem was the same in forward or reverse. i built a pressure guage using an inexpensive guage that reads up to 500 psi and had an adapter hose made to connect it to the 1/8"npt pressure fittings found just below the direction selector valve on the shuttle shift valve. I performed a pressure test of the shuttle valve and found that at idle the pressure on the forward/reverse circuits was barely 50 psi, and at high rpm it was barely 100 psi, spec is 230-255 psi. after messing with the shims for the shuttle pressure regulator i managed to get the pressure up to 75 psi idle and 150 psi at high rpm. still not enough. i looked elsewhere for the pressure problem. i found that the pressure has to go from the pump to the three point lift first before going to the shuttle valve. at the left hand side of the three point control system (below the seat just below the seat bracket is a valve setup with a pipe on it that feeds the shuttle valve. this valve is called the "Flow Priority Valve". in essence it allows two hydraulic systems to use the same pump- in this case the shuttle system and the three point. i took it apart and found that the plunger (part #4 on the attached picture) was stuck in the bore of the valve body. i removed all three plugs (one on top and two others one just above the feed pipe to the shuttle valve (#6) and one on the back side (that is #5) on the diagram. i had to tap the control plunger out using a dowel (it should slide smoothly). to repair the plunger i mounted it hand tight in my drill press and used emery cloth to polish it to the correct size. this will take some time as i would do it a little at a time till it was just right- patience here is a must. when it fit 'just nice' i re-assembled everything and re-checked my pressures. now at idle i have 280 psi and it holds steady at 280 all the way through the rpms. i was able to take the tractor off and in 2wd mode i can now burn out in 4th gear!!
so I'd say its fixed. hope this helps someone not think their tractor is junk. in the end I'd say check that plunger in the flow control valve first, and if its stuck like mine was, fix that BEFORE tearing into the shuttle system. it needs to slide back and forth easily.
