Hydraulic Transmission Case Flushing

Modified pump for case flushing

Case flushing in hydrostatic transmissions is almost essential in extending the life of the transmission. Flushing will substantially reduce pump and motor operating temperatures. The arrangement depends on whether the Hot Oil Shuttle is integral to the motor or is an external block. If it is integral to the motor, the case drain line from the top of the motor should run over to the bottom case drain port on the pump. The upper case drain port on the pump should then run through a cooler or heat exchanger if equipped. Depending on the make of pump, it may be possible to run the case drain line through a designated case return filter, however with some shaft seal arrangements, the seal will not tolerate the back pressure created from pushing oil through the filter, especially cold oil. Please keep in mind that any back pressure in the pumps case drain line will now be additive to the back pressure on the motors case drain line.

If the Hot Oil Shuttle is external to the motor, plumb the relief flow from the Hot Oil Shuttle to the bottom case drain port on the motor, then continue as stated above. The draw back to such an arrangement is that contamination created by the drive motor may end up contaminating the case of the pump, however if that is the case, chances are you already have damage within the pump as well.

This arrangement makes a huge difference on Low Speed High Torque motors that have extremely low case drain flow rates. With these motors, the stagnant case drain oil sits in the case, becomes extremely hot, and looses viscosity and lubricating properties. In a Staffa or KYB motor, the bronze surfacing of the connecting rod then smears on the crank shaft, as well as the connecting rod ball-end and piston gall up. Life on these motors is extended greatly by case flushing.

Caveat – do not exceed maximum recommended case pressures!

Older designs such as Dynapower units had charge pumps that did not relieve into the case of the pump; instead they discharged their charge pump flow across to the suction side of the charge pump. These charge pumps can be modified to discharge relief oil externally, which can then be plumbed into one of the ports in the trunion caps. This makes a huge difference on mobile equipment such as pavers or rollers that spend a lot of time idle over hot tarmac. A picture of such an arrangement is shown here. If you have any interest in this particular modification, please email me and I will provide more details.

Eaton VIS 45 motors are commonly used in grapple rotate applications, however they are the open loop version of the motor which allows drifting in neutral do to the method used to lubricate the bearings and drive spline in the motor. This motor can be arranged as a closed loop motor which will provide proper lubriction and better load holding capability if plumbed correctly.  The complete write up is in this PDF file: Closed_Vs_Open_VIS

Here is an extract:

The Eaton VIS motor is commonly used in grapple rotate applications. The open loop version of the VIS in this application allows rotation drift do to the method used in providing lubrication oil for the inboard shaft bearing and drive splines. The method of lubrication relies on two check valves that seat inside of the valve star.  The port with the highest pressure provides the lubrication for the inboard bearing. The highest pressure unseats it’s ball in the star, and feeds the lubrication passage. The other check valve prevents flow from bypassing through both check valves.

There are two drawbacks to using the highest pressure port to provide the lubrication for the bearing: 1) the high pressure drop creates heat, and 2) When the control valve (in it’s neutral position) is used to hold a load, this load induced pressure is allowed to flow through the check, allowing the load to rotate.

 These motors can be converted to closed loop operation which will reduce the amount of drift experienced. At this time this idea is  theoretical and has not been tried in this application. Modifications of an OEM system may void warranties and must be done at the users own risk.Closed_Vs_Open_VIS

To perform a fast shaft seal replacement on a Poclain MS08/Waratah motor:

Hanson Hydraulics Ltd. Blog article:

A quick reseal on a Poclain MS08-9-12A-A08-1129-DJMO motor. This unit is off of a 622B Waratah processor head. A factory seal kit is around $900.00. In this instance the customer wanted just the shaft seal replaced with absolute minimum down-time.

Ordering the high pressure double lipped shaft seal and housing orings came to $30.00. The following description of work covers only a fast shaft seal replacement. This is not a complete rebuild.

First, note direction of feed wheel. To change the direction, the wheel flips over, allowing the motor and wheel assembly to be used on the other arm. Remove the wheel.

Remove the housing bolts, remove the port end cover, be careful as the distributor may drop out of the cover, usually they stay sitting on the cylinder block, but be careful not to drop it, there are springs that load the distributor up against the cylinder block.

Remove the cam ring and the cylinder block. Remove the snap ring on the shaft, followed by the shims.  It is sometimes necessary to press on the inner bearing race to take the tension of the snap ring in order to get it off.

Support the housing, make sure there is clearance below for the output flange, and press the shaft out.

The outboard cone will remain on the shaft and is not removable without possibley destroying.  This bearing runs outboard of the shaft seal, so it does not get oil. Repack this bearing as is using a grease gun with needle attachment. There is a grease/dust seal between the outboard cone and output flange.  This will not be changed as it would necessitate removal and possible damage to the bearing.

The seal carrier is removed from the housing by driving out towards the cylinder block.  It will not pass through the inboard outer race, so this race will be driven out as well.  Find a driving tool with the largest diameter possible so the seal carrier does not become distorted. Drive or press the assembly out.  There are two seal carriers, the outboard has the double lip shaft seal, and the other has a high pressure PTFE seal.  In this instance the PTFE seal was not changed.

Pay attention to the stepped face on the high pressure seal carrier and make sure it is installed in the same direction.

Replace the double lip seal, applying a film of Ultra Blue to the outside of the seal. Make sure the housing and seal carriers OD are oil free, and apply a film of anaerobic sealant to the outside of the seal carriers.  Press back into the housing, but take as much time as you need to not distort the seal carriers! Be careful!!!. Press the inboard cup into the housing.

Put a film of grease on the lips of the seal, add a bit of grease to the cavity for the outboard bearing, and install the housing over the shaft.  Heat the inboard cone up and install it onto the shaft, followed by the shims and snap ring.

Reinstall the cylinder block, housing oring, cam ring, and install oring into the port end cover.  Clean the distributor and spring, making sure they are free of oil and grease the springs so they will stay stuck in the distributor.

Install the distributor into the port end cover.  Take a small piece of plastic round stock and insert it through one of the ports so that it will hold the distributor in place.  Tension will need to be maintained on the rod or the distributor will drop out, do not let the distributor drop out!!!

While maintaining tension, install the port end cover on top of the motor assembly, tighten the bolts up, If it appears there is any interference among the parts, investigate!!!.

Inner cup and cone A&S 31313F

Outer cup and cone A&S 33214F

Shaft seal BABSL 070090070-1  (70mmx90mmx7mm)

2-178/N1470 oring x2

 * Some units may use a 70mmx110mmx8mm shaft seal

Written for Hanson Hydraulics Ltd. Blog

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. 

Hanson Hydraulics Ltd. Blog article:

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.

Written for Hanson Hydraulics Ltd. Blog