Troubleshooting MTS Belt Untracking Problems Caterpillar

Problem:

It has been reported that on the above product, the MTS belts are untracking on some machines.

Solution:

The following steps can be taken to troubleshoot this problem to ensure the system is working correctly. It is important to first find out the story of how the machine was being used, in what conditions was it in when the track came off and how the track was running before it untracked.

1. Driver wheels / Idler wheels have Asphalt built up in between them. Clean Asphalt out so that the Guide blocks ride properly when traveling.

2. Track alignment issue? Reference Technical Information Bulletin dated November 25, 1998 Subject title "Steps to diagnose and correct the belt tracking". This procedure has been effective in getting the proper alignment of the tracking bar to frame relationship, with the shimming and temperature differential procedure being the critical steps.

3. Tracks in poor condition, missing Guide blocks, or MTS belt torn. Reference "Guideline for Reusable Parts and Salvage Operations" manual SEBF8351 for instructions to determine if the belt is reusable or must be replaced.

4. Loss of Track tensioning pressure.

a. Did the Track tension switch (110-6137) activate the alarm? This switch is normally closed at 1600 PSI and resets at 2000 PSI. The switch circuit must be checked for proper operation. Pin A is the ground, Pin B is normally open with Pin C being the normally closed pin. If you have lost the pressure, you should have 24 VDC through pins A & C. If you have 24 VDC through pins A & B and have lost track tension this switch should be replaced.

b. The track tension accumulator pressures should be checked also. To do this install a 148-1886 coupler to an 8T-0859 (0 to 3600 psi) pressure gage to the remote air bleed port on the tension ram. Rotate the gage to open the high-pressure quick coupler and read pressure. This pressure should be at 2400 ( 50 psi. If this pressure is low, you will need to check the Nitrogen side of the accumulator. (Proceed to step C.) If this pressure is within limits go to step five.

c. To test the nitrogen side of the accumulator the hydraulic pressure side must be bled off. To do this reference the steps in the manuals KENR2875/AP-1055B and KENR2878/BG-2455C section titled " Releasing Track Tension, (Trapped) Oil pressure". Add the two steps in Service Magazine media number - SEPD0412, April 13, 1998 titled "Correction to purging track tension" to the "Releasing Track Tension, (Trapped) Oil Pressure" procedure between step 1 and step 2.

Test for the old 107-6328 Accumulator

* For the old style accumulator part number 107-6328 (See Figure 1) reference the steps in the manual KENR2875/AP-1055B and KENR2878/BG-2455C and precharge to a pressure of 10340 ± 1520kPa (1500 ± 220psi).

NOTE: Refer to the Precharge vs. Temperature chart in order to find the correct accumulator precharge pressure that corresponds to the ambient air temperature.

Figure 1.

Test for the new 134-3684 Uncharged Accumulator

* To test the new style accumulator part number 134-3684 (See Figure 2) you will need a 9U-6740 Charging group and a 151-8856 charging seal.

Figure 2.

1) Remove plug cover and make sure the area doesn't have any paint or grease on it. Be sure that the bleeder side of the gage is closed (clockwise).

2) Loosen Allen plug (Counterclockwise) 1/6 of a turn with a 6 mm Allen wrench. 1/6 Do not loosen plug more than th turn or pressure will be lost!

3) Connect gage assembly to the accumulator first by putting the Allen part of the gage assembly into the plug on the end of the accumulator.

4) Next, hold Allen wrench tee so that it does not turn while threading gage assembly onto the accumulator. Make sure that the gage assembly is tight.

5) Loosen (counterclockwise) the Allen plug 1 to 2 turns. Do not loosen any more than two turns.

6) The gage should read 2200 ( 220 PSI. (See attached Chart 2 for Precharge vs. Temperature.) Hand tighten (clockwise) the Allen plug with the tee on the assembly. Relieve the pressure on the gage by turning the bleed valve counterclockwise. Remove the gage assembly from the accumulator and torque Allen plug to 8.5 ft-lbs. Max.

NOTE: If the accumulator is not serviced to the proper pressure, service with the 9U-6740 Charging Group and 151-8856 Charging Seal per the instructions in kit to 2200 ( 220 psi. Refer to the Precharge vs. Temperature chart in order to find the correct accumulator precharge pressure that corresponds to the ambient air temperature.

d. Once the Nitrogen side has been checked/properly serviced, you will have to recharge the hydraulic side of the accumulator. After this is complete go to step five.

5. The track tension cylinder has air in the ram. It has been found that air in the system will cause the ram to retract during certain conditions and allow the untracking of the track. You will have to purge the air out of the system. To do this, refer to the Service Magazine media number - SEPD0404 publication date 1998/02/16. Section titled "Air bleed procedure for Track Tensioning Ram equipped with the field update kit." The only corrections to this procedure are that item 4(B) should read: Start engine, adjust the auxiliary pump compensator to the pressure of 2400 psi. In addition, Item 5 should be repeated three or more times to ensure that the air is purged out of the system. Item 7 should read: Close the needle valve for the oil supply at the manifold. Note: The maximum torque that should be applied to this valve is 10 ft-lbs. Over torque will result in breakage of the needle valve. (Note: Some failures of this needle valve 123-8923 have been reported due to the breakage of the stem. Reference Service Magazine media number - SEPD0479 publication dated 1999/07/05 titled "New Knob Kit available for Track Tension Manifold.") After the system is purged of air, the Compensator will have to be readjusted to 2100 ± 50 PSI. A bleed hose can be made for this by using the following parts: 122-6887(50 inches), 124-2111, 148-1886, 4J-5477, and 8C-6866 qty. 1 each.

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