Bobcat 463 hydraulic pump failure.
Very slow to operate, no power
This machine arrived in the shop with the complaint that every thing was working very slowly. The dipper arm was sloe to react and the bucket even slower. Even at full RPM nothing really changed. there was a small leak but that could not justify the poor response we were getting from the machine.
The first simple test was to establish if we had a flow problem or a pressure problem. We drove the machine up to the forklift and engaged the bucket. Trying to lift the counter weight of the forklift was futile, there was no power of grunt at all. So it seemed that we had very little pressure and flow. At this point there was a audible whine from the pump area, so we decided to connect a hydraulic flow and pressure gauge.
This device pointed us immediately in the right direction, we were only getting around 1 Bar of pressure at the most and the flow dropped off completely as soon as any load was present. As we had connected the pressure gauge in directly after the pressure side of the pump we had eliminated all the other valves and devices. This made us confident that the problem was the pump and not the valve bank or the pressure relief valve.
With a go ahead from the customer we started the job of getting the pump out of the machine. Now the workshop manual says that this can be removed with the drive pumps in place, in other words the entire pump assembly does not have to be removed. The photo below shows the setup with the two drive dumps and the lift pump right on the end.
Just look at the clearance here, about 15 mm to clear, how do you remove the pump off the spline and get it to clear the chassis?
After removing all the ancillary items such as the levers, linkages, hoses and support braces, we found that it was still impossible to get the pump out. the mounting bolts mentioned in the manual were not accessible and the main discharge hose was lost some where in the chicken nest, as can be seen in the photo below.
Not a pretty sight ! Well that is what it starts to look like after some years of hard work.
You will notice that to get to this stage of the exercise we had to first remove the diesel engine.
Not impossible, but defiantly a challenge.
With the engine out of the way we started the tedious task of cleaning up years of debris that had collected in between the hoses and pumps. Some time later we had the entire pump assembly on the workshop floor.
Just as well we had removed the entire assembly, there were a number of cracks and splits in the mounting brackets. The main bracket that holds the pump assembly to the engine was badly fatigued and was in need of some serious attention.
Notice how the pump mounting bracket broke, with the ear for one of the mountings gone missing completely!
Now to the root of the problem, the hydraulic pump. After removing the pump we stripped her down and this is what we discovered. Can you spot the problem?
Notice the scouring marks on the aluminium casing. What has caused this?
Typical marks left by the pump drive gears, but how does this happen?
well observe the bush in the drive side casing. The bush is worn through on the bottom. Yes right through the white metal, right through the copper to which the white metal is bonded, and into the steel bearing housing.
With this type of wear the poor housing stands no chance, it just gets eaten away but the teeth of the pump gears.
What causes this type of fatigue? Well mostly wear and tear, old age, and in some cases the needle bearings that support the gear shaft collapse. If the bush is not worn but there are score marks on the ally housing then the problem is most probably contamination.
When the gears below get spinning plenty damage can occur when bushes collapse or dirt enters the system.
With a new pump fitted and all the pipes and hoses washed and blown out with compressed air, the pump assembly is returned to the machine. Engine back and all ancillaries connected , and away we go.
Machine now lifts the forklift and operates like an impatient teenager.
Enjoy this You Tube clip that explains hydraulic pump failure.
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