Air System Troubleshooting2019-04-10T15:00:47+00:00

Air System Troubleshooting

Eaton Fuller 8, 9, 10, 11, 13, 15, and 18-Speed Transmission Air System Troubleshooting

Symptoms

  1. Air Leak at Shift Knob
  2. Air Leak at Slave Valve
  3. Air Leak from Transmission Breather or Transmission Case is Pressurized
  4. Air Leak at Splitter Cylinder Cover Exhaust Port
  5. No or Slow Range Shift into Low
  6. No or Slow Range Shift into High
  7. Range Shifts with Shift Lever in Gear

warningWARNING: Use care when removing air lines or checking for air flow from disconnected lines. High-pressure air may exhaust suddenly. Wear safety glasses. Exhaust all air pressure from the system before removing air filter/regulator or combination cylinder cover.

Note: During all testing, the vehicle air pressure must be greater than 90 PSI (620 kPa). If during testing the pressure falls below 90 PSI (620 kPa), make sure the transmission is in neutral, start the engine, and let the pressure build to governor cutoff. After the pressure reaches the governor cut off, continue testing. The pressure is critical if the vehicle is equipped with a Pressure Protection Valve that would shut off the air supply to certain air circuits if the system pressure dropped below a preset level.
IMPORTANT: Use the following air system troubleshooting procedures for part replacement only if the symptom can be duplicated.
If the problem is intermittent, parts that are not defective could be replaced.

1. Symptom – Air Leak at Shift Knob

Normal Operation:

  • A burst of air will be exhausted from the shift knob when moving the range selector from low to high. This is the air being
    exhausted from the “P” air line.
  • A burst of air will be exhausted from the shift knob when moving the splitter button rearward (shifting to low split). This
    is the air being exhausted from the “SP” air line.

Possible Causes:

  • Incorrectly attached air lines
  • Internal leak in slave valve
  • Internal leak at insert valve
  • Internal leak at shift knob

See the table below for troubleshooting steps and possible solutions:

Air Leak at Shift Knob
Procedure Result Next Step
Step 1
Remove lower skirt on shift knob. Check for leaking fitting at the shift knob. Leak found. Repair leaking fitting or air line
No leak found Go to step 2
Step 2
Check air lines to make sure all lines are connected to the proper ports on the shift knob. Air lines are not connected to the proper ports Connect lines properly
A.) Reversal of “S” and “P” lines will result in a constant leak from the exhaust when high range is selected. Air lines are connected to the proper ports. Go to step 3
B.) Reversal of the H/L and “SP” lines will result in a constant leak when the splitter button is rearward.
Step 3
Move the range selector lever down to low range. Check for constant air flow from the exhaust “E” port. Constant air flow from the “E” port. Replace knob
No air flow from “E” port. Go to step 4
Step 4
Move the range selector up to high range. Disconnect the small air line connected to the “P” port of the shift knob. Check for air flow from the
port and air line.
Constant air is leaking from the “P” port or the “E” port. Repair or replace the shift knob.
Air is coming out of the disconnected air line. 1. Verify that the air line is connected to the slave valve “p” port.
2. If properly connected, replace the slave valve.
Air is not leaking from either port or disconnected air line. Go to Step 5
Step 5
Reattach the air line to the “P” port. Move the range selector down to low range and move the splitter button rearward. Disconnect line from the “SP” port. Check for air flowing from the SP port on the shift knob. Air is flowing from the SP line. 1. Check to make sure the “SP” line is connected to the splitter cylinder cover.
2. If the line is properly attached, check that the insert valve (old style) is properly installed (stem facing inward) and that the insert valve bore is not defective.
3. Replace the insert valve.
Air is not flowing from the line. Repair or replace the shift knob

2. Symptom – Air Leak at Slave Valve

Normal Operation:
A momentary exhaust of air at the slave valve occurs during a range shift. The air from the low side of the range cylinder is exhausted as air pressure is applied to the high range side. Likewise, air from the high range side of the piston is exhausted as air pressure is applied to the low range side. The exhaust port is located at the slave valve to transmission mounting interface.
Possible Causes:

  • Internal leak in range cylinder.
  • Internal leak in slave valve.

See the table below for troubleshooting steps and possible solutions:

Air Leak at Slave Valve
Procedure Result Next Step
Step 1 Confirm that air is leaking from the exhaust port on the slave valve and not a fitting or air line. Air is leaking from fitting or air line. Repair or replace fitting or air line.
Air is definitely leaking from slave valve exhaust port. Go to Step 2
Step 2 Move range selector down to select low range. Air is flowing from high range supply port on range cylinder. Remove range cylinder cover andrepair leaking range piston or piston seal. After repair, check for proper range operation.
Remove the 1/4″ I.D. rubber air line at the high range supply port on the range cylinder.
Feel for air flow from the open port on the range cylinder.
Notice if the air leak at the slave valve only occurs when the transmission is in high range.
Repeat the above test but remove the low range air hose and check with high range selected.
No air flow from high range port. Repair or replace slave valve.

3. Symptom – Air Leak from Transmission Breather or Transmission Case is Pressurized

Normal Operation:
There should be no measurable air flow from the transmission breather.
Possible Causes:

  • Leak at range yoke bar O-ring
  • Leak at splitter yoke bar O-ring

Air Leak from Transmission Breather or Transmission Case is Pressurized
Procedure Result Next Step
Step 1 Listen for the air leak with the transmission shifted to both low and high range. Leak is only in low range. Remove range cylinder and inspect for damaged range yoke bar, yoke bar O-ring, or range cylinder. Repair as necessary.
Leak is in both low and high range. Remove splitter cylinder. Inspect for damaged splitter yoke bar, O-ring, or cylinder. Repair as necessary.

4. Symptom – Air Leak at Splitter Cylinder Cover Exhaust Port

Normal Operation:
A burst of air will exhaust from this port when shifting into low split (the splitter button is moved rearward while in low range).
Possible Causes:

  • Damaged/defective insert valve
  • Leak past insert valve external O-rings
  • Leak past splitter cylinder piston

Air Leak at Splitter Cylinder Cover Exhaust Port
Procedure Result Next Step
Step 1 (old style) Remove insert valve. Check for contamination, damaged seals, or sticky movement. Check the insert valve bore in the splitter cylinder cover for contamination or damage which would result in leakage past the insert valve O-rings. Contamination or damage found. Repair or replace as necessary.
No contamination or damage found. Go to Step 2
Step 2 Remove the splitter cylinder cover and piston. Check the piston bore for contamination or damage. Check the piston seals for damage. NOTE: Early production transmissions used a paper gasket to seal the splitter cover to cylinder, if necessary, replace this configuration with the spool valve design which uses an O-ring. Contamination or damage found. Repair or replace as necessary.

5. Symptom – No or Slow Range Shift into Low

Normal Operation:
When the range selector on the shift knob is moved down to select low range, air pressure will flow through the shift knob to the “P” port on the slave valve. The slave valve will direct air pressure through the low range 1/4″ rubber hose to the range cylinder to shift the range. There will be a brief burst of air at the slave valve as the high range side of the range piston exhausts. Likewise, when high range is selected, the air pressure in the “P” will be exhausted at the shift knob. This will cause the slave valve to direct air to the rear side of the range cylinder piston. The air pressure on the low range side will be exhausted at the slave valve.
Possible Causes:

  • Incorrect air line hook up
  • Insufficient air supply to transmission
  • Damaged or defective air filter / regulator assembly
  • Damaged or defective shift knob master valve
  • Damaged or defective slave valve
  • Damaged or defective range cylinder
  • Damaged or defective range yoke or yoke bar
  • Damaged or defective range synchronizer
  • Damaged or defective gearing in auxiliary section of transmission

No or Slow Range Shift into Low
Procedure Result Next Step
Step 1 (old style) Place the shift lever in neutral. Check for constant air leakage at the shift knob, slave valve, and transmission case
breather when both low and high range have been selected.
Constant air leak is detected. Go to the other corresponding symptom first. See beginning of Air System Troubleshooting section.
No constant leak is detected. Go to Step 2
Step 2 Place shift lever in neutral. Move range selector up to high range position. At the rear of the transmission, disconnect the 1/4″ rubber air line from the low range supply port on the range cylinder. Check for air flow from the low range port. Air flows from the low range port. Remove range cylinder cover and repair leaking range piston or piston seal.
No air flow from low range port. Go to Step 3
Step 3 Check for air flow from the disconnected air line. Air flows from disconnected air line. Go to step 6.
No air flows from disconnected air line. Go to Step 4
Step 4 Install a 100 PSI air gauge in the disconnected air line end. With the shift lever in neutral, move the range selector down to select low range. Observe the gauge The gauge read 0 PSI. Go to step 6.
The gauge reads pressure but is lower than 58 PSI or higher than 63 PSI. Replace the filter/regulator and check for proper range operation.
The gauge reads between 58 – 63 PSI. Go to Step 5
Step 5 Confirm that shift lever is still in neutral. Have an assistant move the range selector up and down between low and high range. Does the pressure measured at the gauge respond rapidly when going from high to low? Pressure rapidly changes between 58-63 PSI and 0 at the gauge. Air system appears to be operating satisfactory. Go to step 10.
Pressure does not change rapidly at gauge. 1. Check for a plugged or dirty filter in the filter/regulator assembly.
2. Check for a pinched or obstructed 1/4″ rubber air line between the filter/regulator and slave valve.
3. Check for a pinched or obstructed 1/4″ rubber air line between the slave valve and the test gauge.
4. If all are satisfactory, go to step 6.
Step 6 Place shift lever in neutral. At the shift knob, move the range selection lever up to select high range. At the slave valve, remove the air line from the “P” port. (should be a black line). Check for air flow from the disconnected line. Air flows from the disconnected line. 1. Confirm that the air lines are connected to the correct ports at the shift knob.
2. If the lines are correct, replace the shift knob.
No air flow from the disconnected line. Go to Step 7
Step 7 Check for air flow from the “P” port on the slave valve. Air flows from this port Replace the slave valve.
No air flows from this port Go to step 8
Step 8 Place the shift lever in neutral. Install a 100 PSI pressure gauge in line with the “P” line. Move the range selector back and forth from low to high range. The gauge should show rapid pressure change. The gauge responds slowly. 1. Check for a restricted line between the shift knob and slave valve.
2. If the lines are correct, replace the shift knob.
3. Check for a plugged or dirty filter in the filter / regulator assembly.
4. Check for a pinched or obstructed 1/4″ rubber air line between the filter/regulator and slave valve.
5. Check for a pinched or obstructed air line between the slave valve and the “S” port on the shift knob.
6. If all are good, replace the shift knob.
The gauge rapidly moves between 58-63 PSI and 0 PSI. Go to step 9.
Step 9 If possible, leave air lines attached to slave valve. Unbolt the slave valve from transmission side. Check for free movement of the plunger pin protruding from the case under the slave valve. The pin should extract when the transmission is shifted into gear and retract when shifted into neutral.
NOTE: If desired, the slave valve can be actuated and tested while unbolted from the  transmission case. The air lines, of course, must remain attached.
Actuating plunger pin does not move freely 1. Remove actuating plunger pin and check for damage.
2. Check for missing or broken spring.
Actuating plunger pin moves freely. Repair or replace slave valve and check for proper range operation.
Step 10 If air system has been tested and found to operate satisfactory, the auxiliary section must be removed to inspect for mechanical
problem. Remove auxiliary section and inspect for:
•Binding of range yoke bar or piston
•Damaged or defective range yoke
•Damaged or defective range synchronizer
•Cracked countershaft weld resulting in gear turning on shaft
•Damaged or defective range sliding clutch
•Auxiliary section gearing out of time

7. Symptom – No or Slow Range Shift into High

Normal Operation:
When the range selector on the shift knob is moved down to select low range, air pressure will flow through the shift knob to the ‘P” port on the slave valve. The slave valve will direct air pressure through the low range 1/4″ rubber supply hose to the range cylinder to shift the range. There will be a brief burst of air at the slave valve as the high range side of the range piston exhausts.
Likewise, when high range is selected, the air pressure in the “P” will be exhausted at the shift knob. This will cause the slave valve to direct air to the rear side of the range cylinder piston. The air pressure on the low range side will be exhausted at the slave valve.
Possible Causes:

  • Incorrect air line hook up
  • Insufficient air supply to transmission
  • Plugged filter
  • Incorrect regulator pressure
  • Damaged or defective shift knob master valve
  • Damaged or defective slave valve
  • Damaged or defective range cylinder
  •  Damaged or defective range yoke or yoke bar
  •  Damaged or defective range synchronizer
  •  Damaged or defective gearing in auxiliary section of transmission

No or Slow Range Shift into High
Procedure Result Next Step
Step 1 Place the shift lever in neutral. Check for constant air leakage at the shift knob, slave valve, and transmission case breather when both low and high range have been selected. Constant air leak is detected. Go to the other corresponding symptom first. See beginning of Air System Troubleshooting section.
No constant leak is detected. Go to Step 2
Step 2 Place shift lever in neutral. Move range selector down to low range position. At the transmission rear, disconnect the  1/4″ rubber air line from the range cylinder high range supply port. Check for air flow from the cylinder high range port. Air flows from the high range port. Remove range cylinder cover and repair leaking range piston or piston seal. After repair, check for proper range operation.
No air flow from high range port. Go to Step 3
Step 3 Check for air flow from the disconnected air line. Air flows from disconnected air line. Go to step 6.
No air flows from disconnected air line. Go to Step 4
Step 4 Install a 100 PSI air gauge in the disconnected air line end. With the shift lever in neutral, move the range selector down to select high range. Observe the gauge The gauge read 0 PSI. Go to step 6.
The gauge reads pressure but is lower than 58 PSI or higher than 63 PSI. Replace the filter/regulator and check for proper range operation.
The gauge reads between 58 – 63 PSI. Go to Step 5
Step 5 Confirm that shift lever is still in neutral. Have an assistant move the range selector up and down between low and high range. Does the pressure measured at the gauge respond rapidly when going from high to low? Pressure rapidly changes between 58-63 PSI and 0 at the gauge. Air system appears to be operating satisfactory. Go to step 10.
Pressure does not change rapidly at gauge. 1. Check for a plugged or dirty filter in the filter/regulator assembly.
2. Check for a pinched or obstructed 1/4″ rubber air line between the filter/regulator and slave valve.
3. Check for a pinched or obstructed 1/4″ rubber air line between the slave valve and the test gauge.
rubber air line between the slave valve and the test gauge.
5. If all are satisfactory, go to step 6.
Step 6 Place shift lever in neutral. At the shift knob, move the range selection lever up to select high range. At the slave valve, remove the air line from the “P” port. (should be a black line). Check for air flow from the disconnected line. Air flows from the disconnected line. 1. Confirm that the air lines are connected to the correct ports at the shift knob.
2. If the lines are correct, replace the shift knob.
No air flow from the disconnected line. Go to Step 7
Step 7 Check for air coming out of the slave valve “P” port. Air flows from this port Replace the slave valve.
No air flows from this port Go to step 8
Step 8 Place the shift lever in neutral. Install a 100 PSI pressure gauge in line with the “P” line. Move the range selector back and forth from low to high range. The gauge should show rapid pressure change. The gauge responds slowly. 1. Check for a restricted line between the shift knob and slave valve.
2.Check for a restricted exhaust port on the shift knob.
3. Check for a plugged or dirty filter in the filter / regulator assembly.
4. Check for a pinched or obstructed 1/4″ rubber air line between the filter/regulator and slave valve.
5. Check for a pinched or obstructed air line between the slave valve and the “S” port on the shift knob.
6. If all are good, replace the shift knob.
The gauge rapidly moves between 58-63 PSI and 0 PSI. Go to step 9.
Step 9 If possible, leave air lines attached to slave valve. Unbolt the slave valve from  transmission side. Check for free movement of the plunger pin protruding from the case under the slave valve. The pin should extract when the transmission is shifted into gear and  retract when shifted into neutral. If desired, the slave valve can be actuated and tested while unbolted from the transmission case. The air lines, of course, must remain attached. Actuating plunger pin does not move freely 1. Remove actuating plunger pin and check for damage.
2. Check for missing or broken spring.
Actuating plunger pin moves freely. Repair or replace slave valve and check for proper range operation.
Step 10 If air system has been tested and found to operate satisfactory, the auxiliary section must be removed to inspect for mechanical problem. Remove auxiliary section and inspect for:
•Binding of range yoke bar or piston
•Damaged or defective range yoke
•Damaged or defective range synchronizer
•Cracked countershaft weld resulting in
gear turning on shaft
•Damaged or defective range sliding clutch
•Auxiliary section gearing out of time

7. Symptom – Range Shifts with Shift Lever in Gear

Normal Operation:
Range shifts should only occur when the shift lever is in neutral. The range selector can be moved up or down while the shift lever is in a gear position, but the shift will not occur until the shift lever is moved to neutral.
Possible Causes:
• Worn or missing actuating pin or air valve shaft
• Worn shift rail
Procedure:
If the range has been confirmed to shift with the shift lever in gear, unbolt the slave valve from the side of the transmission. Confirm that the actuating pin is present and that it is the proper part number for the corresponding slave valve. If correct, remove the shift bar housing assembly and check for a worn or damaged air valve shaft or worn shift rails. Replace necessary parts.

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