Shimadzu Gear Pump, Bent Gear Teeth

Shimadzu gear pump failure: on a Caterpillar dozer. Here are some pictures of a recent gear pump failure. It is a Shimadzu gear pump from a D5C cat. It is the implement pump. This particular Cat has a core drill mounted to the back of it which is supplied oil from the ripper control valve. 
Before dissmantling
The main implement control valve has a pilot operated main relief as well as a direct acting work port relief for the ripper down port.  Oil from the ripper down port feeds the control valve that operates the functions of the core drill. This control valve also has a direct acting relief.
In an effort to increase available pressure at the core drill, the main relief valve  and ripper relief setting was increased. The particular shop that was working on the machine must not have been aware of the relief at the drill.  The relief at the drill was the pressure limiting factor, however the two reliefs on the implement control valve were left substantially increased.  All was well until implement fuctions were activated and dead headed that did not have work port reliefs. 
Gear teeth bent back from excessive pressure
This sudden increase in pressure bent the teeth of the gears back, producing excessive tip clearance. This resulted in a decrease in performance, as well as a decrease in maximum available pressure, as in a dead headed state, the entire volume of oil was bypassing across the gears tip clearance, overheating the oil and eventually blistering the paint on the pump.

Beyond economical repair

Situations like this can be avoided by 1) find out exactly why the pressure won’t increase past a certan level when increasing the main relief setting. The question must be asked, “where is the oil going?” and 2) always be sure to readjust the main relief pressure after making work port pressure adjustments.
The most common over pressure failures on gear pumps are split gear housings or extruded seals or extreme gear housing wear, but on this particular make of pump it seems the weak link is the amount of material at the base of the tooth.  I have heard of similar Shmadzu gear pump failures on Komatsu dozers.