Repair of the A4VG40 Pump – What Did the Disassembly Reveal?
A4VG hydraulic pumps are among the most commonly found in construction machinery. With a wide range of configuration options and various variants (from 40 to 125 cm³/rev and larger), they are suitable for loaders, excavators, conveyors, and concrete mixers. This is an example that a device "for everything" does not have to be useless – on the contrary, flexibility makes it an extremely versatile solution.
A4VG40 – Drive and Rotation Pump in One
In our workshop, we received an A4VG40 pump from a loader, where it served as a drive pump. With minimal cost – by replacing the regulator and removing the start valve – the same model can also be used as a rotation pump in excavators. This is a significant advantage of this design.
Unfortunately, the unit that came to us had "weakened," and there was an additional problem with zeroing the pump. The diagnosis could only be one – disassembly and detailed verification were necessary.
Disassembly Step by Step
The first element that was checked was the gear pump responsible for the preliminary supply of the unit. Here, we already noticed scratched gears – a clear signal that metal shavings were circulating in the system. Next, we disassembled the closing plate and the rotary group. It turned out that:
- there were damages to the working surfaces,
- there were visible wear marks from the bearings,
- the ball and pistons were scratched,
- and the cause of the entire failure turned out to be worn basket bearings.
These are the components that most often fail in the lower part of A4VG pumps – the balls gradually wear down the swash plate, leading to its blockage. The effect? Destruction of the entire rotary group and contamination of the system with shavings.
Scope of Repair
In this case, the extent of the damage included, among others:
- complete rotary group,
- bushings and sliding bearings,
- swash plate,
- pistons, ball, separator, and disc springs,
- cylinder.
Fortunately, the pump housing was not damaged, which allowed for a decision to be made about a more economical solution – the client used a pump readily available from our stock.
Why Is It Important to React Quickly?
Hydraulics does not forgive delays. One damaged bearing leads to the failure of the entire group, and shavings contaminate the entire system. That is why it is so important to react quickly to the first symptoms – drops in pressure, noises, or problems with the pump operation. Early diagnosis helps avoid a cascade of costly repairs.
The entire video can be seen here.
