Case 1816B hydro problem

[wford]

I've spent the summer trying to solve a weak left-side drive. The pump is a Sunstrand 15-series coupled to a TRW Ross MAB motor. The pump recently had new seals and was lapped then tested to 3000 psi for 20 minutes at a Hydraulic Repair facility. The motor has a new rebuild kit and was lapped after visual inspection but couldn't be tested by the Repair facility for lack of proper spline coupling. When in operation, the unit performs OK as you move the control lever forward (or backward) until you are about half way to maximum speed. According the the system pressure gauge, when the pressure builds to about 1500-1800 psi, the left side falls to zero on system pressure and charge pressure. The right side continues to function normally. And, the left side will return to "normal" once the lever is moved to neutral and then moved forward again. Until the pressure falls to zero on the left side, the torque motor has very good power. If you put the skid steer against an immovable object, the unit will spin the tires until it reaches the 1500-1800 psi threshold. This lemon is a real pain to work on, and I'm growing tired of tearing the thing down and putting it back together with no resolution to the problem. Can anyone help? Thanks!

 

[Tazza]

I wonder if it could be a relief, but it should have shown up when they did the test...... If you move the motors from side to side, does the problem move?

 

[wford]

I wonder if it could be a relief, but it should have shown up when they did the test...... If you move the motors from side to side, does the problem move?

Tazza, thanks for the reply. I've always thought it acts like a faulty relief valve, but haven't found any problem. I inspected the charge pump relief valve - it was clean and appeared to be in good working order. The charge pump operates at spec of 50 psi until the pressure dumps to zero. I inspected the two check valves and they were clean and in good working order. The three valves were also inspected by the Repair Facility. I don't know if the test truly replicates conditions as it would if pump is coupled to a motor...and I don't really know how they went about testing it, but the tech is known to do a good job. Since it is such a pain to work on, I've put off removing both motors and switching them until now - thought the repair facility testing would locate a problem. Rather than remove the motors, I may get a couple of longer hoses and just couple the right pump to the left motor and see what happens. When there is no resistance on the motors (up on blocks), the left side won't fall to zero pressure - only when there is some load on it, causing it to produce more than 1500-1800 psi. I'm concerned about the charge pressure falling zero and not providing lubrication to the pump, but the pump hasn't failed during the time that this has been a problem, so I don't know...

 

[the.hogman]

Tazza, thanks for the reply. I've always thought it acts like a faulty relief valve, but haven't found any problem. I inspected the charge pump relief valve - it was clean and appeared to be in good working order. The charge pump operates at spec of 50 psi until the pressure dumps to zero. I inspected the two check valves and they were clean and in good working order. The three valves were also inspected by the Repair Facility. I don't know if the test truly replicates conditions as it would if pump is coupled to a motor...and I don't really know how they went about testing it, but the tech is known to do a good job. Since it is such a pain to work on, I've put off removing both motors and switching them until now - thought the repair facility testing would locate a problem. Rather than remove the motors, I may get a couple of longer hoses and just couple the right pump to the left motor and see what happens. When there is no resistance on the motors (up on blocks), the left side won't fall to zero pressure - only when there is some load on it, causing it to produce more than 1500-1800 psi. I'm concerned about the charge pressure falling zero and not providing lubrication to the pump, but the pump hasn't failed during the time that this has been a problem, so I don't know...

I know this is a very old thread but I am curious as to the outcome. What was causing the issue of the pressure drop? Was it somethng so simple as a loose belt on the pump? Thanks!

 

[wford]

I know this is a very old thread but I am curious as to the outcome. What was causing the issue of the pressure drop? Was it somethng so simple as a loose belt on the pump? Thanks!

Hogman, the short answer was the belt on the left pump. I found it by plumbing in a test set on the left side and running the pressure up until the left side lost pressure. What happened is that when the pressure reached 1800 psi the belt would slip -- no smoke or no squealing -- just slip; and it would stop slipping and pull once the pressure fell below 1800 psi. The right side would always function normally. Although the belt tension always seemed to be within spec, it appears that the clutch assembly was not equalizing, so I disassembled that whole clutch mechanism, cleaned it, re-assembled, and adjusted the belt tension to be very tight. No problems have re-appeared. I never would have detected that problem without the test set in place and leaning over the back of the unit to watch the drive assembly while under full power. I wasted a lot of time on this one ... Grrr.