Testing and Adjusting

Service Information System

Friday, January 29, 2016

2:49 PM

Testing and Adjusting

D6H TRACTOR HYDRAULICS

Media Number -SENR3244-00 / Publication Date -01/02/1986 / Date Updated -11/10/2001

Testing And Adjusting

Troubleshooting

Problem 1: Noise from the pump, cylinder movement is not smooth and regular and a sample of oil from the tank has air bubbles in it.

The probable cause of these problems is air in the system. The noise from the pump is caused by cavitation (air bubbles at the inlet side); the cylinder that does not work smoothly is caused by the compression of air; and the air bubbles in the oil are caused by a leak in the system.

1. Check the hose and connections between the tank and the pump for leaks. If oil can leak out when the machine is setting idle, air can leak in when the pump is working.

2. Check the level of oil in the oil tank. If the level of the oil is below the return line, air can get into the oil.

3. Another cause of air in the oil is low oil viscosity. Make reference to the MAINTENANCE GUIDE.

Problem 2: The oil in the system gets too hot.

There are many factors that can cause heat in the hydraulic system. The common causes are: low oil level in the tank, a short rapid duty cycle, a pressure setting on the relief valve that is too low, a restriction in a line that causes an orifice effect.

1. Low oil level in the oil tank. Check the oil level. Add oil if it is low. Check the lines, hoses, connections, valves and cylinders for leaks.

2. If the duty cycle of the machine is short and fast, the temperature of the oil can become high. When oil temperature goes above 98.8°C (210°F) it destroys oil seals in the system.

3. A low setting for relief valve opening will also cause higher temperature in the system oil. This can be corrected by an adjustment to the relief valve that gives an opening pressure according to specification.

4. A more difficult cause to find is a restriction in an oil line. A restriction in the pump supply line will reduce the flow of oil to the pump and cause the pump to become very hot. A restriction in a line that is between the pump and the implements will cause a reduction in efficiency and high oil temperature. Removal of the restriction will normally remove the problem.

Problem 3: Oil delivery by the pump is not according to specification.

There are many reasons why a pump is not delivering oil. Problem 2 shows that a restriction in the supply line to the pump will reduce the flow of oil. If the quantity of oil in the system is low, the pump delivery will be low. Low oil level in the system can cause aeration (air in the oil). Aeration in turn can cause cavitation at the pump. This will cause less output from the pump. If the viscosity of the oil is too high, there will be a decrease in the flow of oil from the pump. A badly worn pump or one that has not been correctly assembled will also cause less output flow.

1. Check the supply line to the pump for a restriction. Check the tank to be sure there is not a restriction in the supply line to the pump.

2. Check the level of the oil in the oil tank. Make reference to the MAINTENANCE GUIDE.

3. Check the type of oil used in the system. Make reference to the MAINTENANCE GUIDE.

4. Remove and inspect the pump. Check it for wear and be sure that it is assembled correctly.

Problem 4: Oil pressure in the system is too low.

This problem is normally caused by leakage in the system, the opening pressure of the relief valve is too low, or a bad pump.

1. Carefully check the system for leakage. Remember that leakage inside a control valve cannot be easily seen.

2. Check the opening pressures of the two relief valves in this system.

3. Remove and inspect the pump for damage and correct assembly.

NOTE: Low oil flow from the pump will cause low oil pressure in the system. See Problem 3.

Problem 5: Loss of efficiency in the implement circuits. (Slow cylinder movement and loss of pressure.)

The probable cause for this problem is normally the same as the causes for Problems 3 and 4. Low oil output from the pump, leakage in the system and the opening pressure of the relief valve is too low. Check Problems 3 and 4 for solutions to this problem. Also check all control linkages for full travel of control valve spools.

Problem 6: Cylinder drift that is more than specification.

For the cause of this problem, see the DRIFT TESTS for the different circuits.

Problem 7: Slow (or loss of) movement in the bulldozer lift, bulldozer tilt or ripper lift circuits.

If the problem is not caused by low pump pressure or output, then the control valve linkage, control valves or oil lines could be the problem.

1. Check control valve linkage for damage or incorrect adjustment.

2. Check main relief valve pressure.

3. Check the operation of the charging valve in the inlet valve group.

4. Check the control valves for damage or contamination that could cause valves not to function correctly.

5. Check oil lines to cylinders for leaks or restrictions.

6. Check cylinders for piston seal leakage.

Testing And Adjusting

Hydraulic oil, under pressure, can remain in the hydraulic system on this machine after the engine and pump have been stopped. Serious injury can be caused if this pressure is not released before any work is done on the hydraulic system. To release any pressure, move the hydraulic control levers into all positions after the engine is off. When the bulldozer control lever is moved to FLOAT position, the bulldozer will move down (drop) suddenly. When the ripper control lever is moved to LOWER position, the ripper will drop suddenly.
The bulldozer and ripper must be flat on the ground before service work is started.
Always move the machine to a location away from the travel of other machines. Be sure that other personnel are not near the machine when the engine is running and tests or adjustments are made.

During a diagnosis of the hydraulic system, remember that correct oil flow and pressure are necessary for correct operation. The output of the pump (oil flow) increases with an increase in engine speed (rpm) and decreases when engine speed (rpm) is decreased. Oil pressure is caused by resistance to the flow of oil.

Visual checks and measurements are the first step when troubleshooting a possible problem. Then do the Operation Checks and last the Instrument Tests.

Use the 5S5123 and 6V4161 Hydraulic Test Groups, a stop watch, a magnet, a thermometer and a mm (inch) ruler for basic tests to measure:

1. The opening pressure of the relief valve for the system. Relief valve pressure that is too low will cause a decrease in the lift, dig and rip characteristics of the machine. Opening pressure that is too high will cause a decrease in the life of hoses and components.

2. Drift rates in the lift and tilt circuits: Circuit drift is caused by leakage past cylinder pistons, O-ring seals in the control valves, load check valves or makeup valves that do not seal correctly or bad adjustment or fit in the control valves.

3. Cycle times in the lift and tilt circuits: Cycle times that are longer than shown in the charts are the result of leakage, pump wear and/or pump speed (rpm).

If the basic tests give an indication of circuit leakage, install a flow meter and do a system test. This procedure will find the source of the leakage.

Visual Checks

A visual inspection of the hydraulic system and its components is the first step when a diagnosis of a problem is made. Stop the engine, lower the blade and the ripper to the ground. To remove the tank filler cap, slowly turn the filler cap until it is loose. If oil comes out the bleed hole, let the tank pressure lower before the filler cap is removed. Make the following inspections:

1. Measure the oil level.

2. Look for air in the oil that is in the tank. Do this immediately after the machine is stopped. Use a clear bottle or container to get a sample of the oil. Look for air bubbles in the oil that is in the bottle.

3. Remove the filter elements and look for particles removed from the oil by the filter element. A magnet will separate ferrous particles from nonferrous particles (piston rings, O-ring seals, etc.).

4. Inspect all oil lines and connections for damage or leaks.

5. Inspect control linkage for bent, broken or damaged components.

Checking Pump Efficiency

For any pump test, the pump flow, measured in U.S. gpm (liter/min) at 100 psi (690 kPa) will be larger than the pump flow at 1000 psi (6900 kPa) at the same rpm.

The difference between the pump flow of two operating pressures is the flow loss.

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*Numbers in examples are for illustration and are not values for any specific pump or pump condition. See SPECIFICATIONS FOR D6H TRACTOR HYDRAULICS, Form SENR3243, for pump flow of a new pump at 100 psi and 1000 psi.

Flow loss when expressed as a percent of pump flow is used as a measure of pump performance.

Example of finding percent of flow loss:

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If the percent of flow loss is more than 10%, pump performance is not good enough.

Test On The Machine

Install a flow meter. Run the engine at 1900 rpm. Measure the pump flow at 100 psi (690 kPa) and at 1000 psi (6900 kPa). Use these values in Formula I.

Formula I:

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Test On The Bench

If the test bench can be run at 1000 psi and at full pump rpm, find the percent of flow loss using Formula I.

If the test bench cannot be run at 1000 psi at full pump rpm, run the pump shaft at 1000 rpm. Measure the pump flow at 100 psi (690 kPa) and at 1000 psi (6900 kPa). Use these values in the top part of Formula II. For the bottom part of the formula, run the pump shaft at 2000 rpm. Measure the pump flow at 100 psi.

Formula II:

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Operation Checks

The operation checks can be used to find leakage in the system. They can also be used to find a bad valve or pump. The speed of rod movement when the cylinders move can be used to check the condition of the cylinders and the pump.

Raise and lower the blade and ripper several times. Operate the tilt control valve until the tilt cylinder is fully extended and retracted several times.

1. Watch the cylinders as they are extended and retracted. Movement must be smooth and regular.

2. Listen for noise from the pump.

3. Listen for the sound of the relief valve opening. The opening pressure of the relief valve is given in the subject, PRESSURE TEST OF THE MAIN RELIEF VALVE.

Cylinder Speed Tests

All speed test are made with the engine at maximum rpm.

System speeds that are the same as those given in the chart is an indication that the circuit operation is normal. The relief valve must be tested to be sure that the opening pressure of each is correct. (See chart for settings.)

If only one of the cylinder speeds is slow, check that circuit for cylinder drift.

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If the travel time is not correct:

1. Check pump efficiency.

2. Check the setting of the relief valve.

3. Check the cylinders for leakage.

4. The makeup valves could have leaks.

5. The valve spools in the bulldozer control valves and in the ripper control valve could be worn.

Drift Tests for Bulldozer Lift Cylinders

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TEST NO. 1: Raise the front of the machine off the ground by lowering a level blade. Put the control lever in HOLD position. Shut off the engine and watch the lift cylinder rods for movement.

TEST NO. 2: Raise the front of the machine off the ground by lowering a level blade. Shut off the engine. Hold the lift control lever in LOWER position. Watch the lift cylinder rods for movement.

TEST NO. 3: Raise the blade off the ground. Put the control lever in HOLD position. Shut off the engine and watch the lift cylinder rods for movement.

TEST NO. 4: Raise the blade off the ground. Shut off the engine. Hold the lift control lever in RAISE position. Watch the lift cylinder rod for movement.

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Drift Tests for Bulldozer Tilt Cylinder

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TEST NO. 1: Put the blade flat on the ground. Raise the front of the machine off the ground by lowering the right side of the blade (TILT RIGHT). Put the tilt circuit in HOLD position. Shut off engine and watch the tilt cylinder rod for movement.

TEST NO. 2: Put the blade flat on the ground. Raise the front of the machine off the ground by lowering the right side of the blade (TILT RIGHT). Shut off engine. Hold tilt control lever in TILT RIGHT position. Watch tilt cylinder for movement.

TEST NO. 3: Put the blade flat on the ground. Raise the front of the machine off the ground by lowering the left side of the blade (TILT LEFT). Put the tilt circuit in HOLD position. Shut off the engine and watch the tilt cylinder rod for movement.

TEST NO. 4: Put the blade flat on the ground. Raise the front of the machine off the ground by lowering the left side of the blade (TILT LEFT). Shut off the engine. Hold tilt control lever in TILT LEFT position. Watch tilt cylinder for movement.

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Drift Tests for Ripper Lift Cylinder

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TEST NO. 1: Raise the rear of the machine off the ground by lowering the ripper. Put the ripper control lever in HOLD position. Shut off the engine and watch the ripper lift cylinder rod for movement.

TEST NO. 2: Raise the rear of the machine off the ground by lowering the ripper. Put the ripper control lever in HOLD position. Shut off the engine. Hold the ripper control lever in LOWER position and watch the ripper cylinder rod for movement.

TEST NO. 3: Raise the ripper off the ground. Put the control lever in HOLD position. Shut off the engine and watch the ripper lift cylinder rod for movement.

TEST NO. 4: Raise the ripper off the ground. Shut off the engine. Put the ripper control lever in RAISE position and watch the ripper cylinder rod for movement.

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Pressure Test Of The Main Relief Valve

The main relief valve is installed in the inlet valve group that is part of the implement control valve group. It is in all the implement hydraulic circuits.

Before making the pressure test, move the machine to a location where the blade can be lowered and will be level on the ground (floor). Get the hydraulic oil to operating temperature. Stop the engine. Move the control lever for the bulldozer and ripper (if equipped) to each operation position several times to take the pressure out of the lines.

Make reference to Warning on first page of Testing and Adjusting section.

Main Relief Valve

6V4161 Hydraulic Test Group

1. If the tractor has a ripper or a tilt cylinder, go to Step 2. If not, get two blocking plate assemblies from the hydraulic test group. Disconnect the rod end hydraulic line from each lift cylinder and install a blocking plate assembly (1) in each line.

2. Put a 0 to 28 000 kPa (0 to 4000 psi) pressure gauge on the 6V3081 Hose.

3. Remove the floor from the tractor.

4. Go through the opening (floor removed) and connect the gauge and hose to pressure tap (2).

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BLOCKING PLATE INSTALLATION (Typical Example)

1. Blocking plate assembly.

5. Start and run the engine at maximum rpm. If the tractor has a ripper or a tilt cylinder, lift the ripper as high as it can move or raise the blade and tilt it all the way to the right. If not, lift the bulldozer blade as high as it can move. Look at the test gauge and slowly move the control lever to the RAISE or TILT RIGHT position (bulldozer lever or ripper lever to the RAISE position or bulldozer lever to the TILT RIGHT position). The high reading on the gauge is the pressure setting of the main relief valve. The pressure setting of the main relief valve is 19 800 + 700 - 0 kPa (2875 + 100 - 0 psi). Do not hold the lever in the RAISE position at relief valve pressure for more than 10 seconds. If more time is needed, wait one minute before moving the control lever again.