Cavco Machine Tool Rebuilding Maintenance Tips: Close Coupled Hydraulic Pump / Motor Failures
Cavco Machine Tool Rebuilding News

There are no “simple motor bearing failures” or “simple hydraulic pump failures,” if one or the other fails, when they are close coupled. One invariably takes out the other.

You'll recognize a close coupled hydraulic pump/motor assembly (or any close coupled assembly for that matter) when the motor shaft does not extend out of the front motor housing. Instead it is bored and broached to accept the keyed input shaft of the pump. It is cheaper to produce but when it fails, it can cause extensive down time for the following reasons:

- When a front motor bearing fails, the heat will destroy the front seal of the pump.
- If a pump fails, it takes out the key-way in the motor. If you try to replace only the pump, the resulting poor fit (pump key to motor key-way) will cause premature failure.
- Motors with female ends aren’t as readily available as the standard motor with a front shaft.
- Pumps usually outlast motors, but they are not usually stock items. There’s nothing worse than an OEM telling you that there is a pump in stock, but they don’t know what it goes to or if it will fit your machine. (This actually happened, very recently.)
- You have to add retrofit design time and parts order/delivery time once you establish that you can’t order a direct replacement assembly. The new design needs to incorporate what is on the shelf.

We have seen all of the above while repairing machines in the field. A “simple motor bearing failure” takes more than a week of down time, even though parts are flown in from all over the country. Recently, we had a motor bearing seize and spin on the motor shaft. This clamped the input shaft of the pump in the motor. The motor and the pump had to be cut apart, which proved to be a waste of time since both were NG.

We have seen so many problems in the field with close coupled pumps/motors, we now advise our customers to replace those assemblies with a standard motor, pump, three piece coupling and interface, to avoid unacceptable down time with critical machines.

Contact Cavco Machine tool Rebuilding at 860-355-1382 for further information