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Caterpiller D5G WGB01981, Dozer will only track FWD. in a R.H.

turn. Dealer diagnosed as FRONT...
Caterpiller D5G WGB01981, Dozer will only track FWD. in a R.H. turn. Dealer diagnosed as FRONT L.H. pump stuck in high. Question: Then why when you command FWD. FULL speed. Does the dozer then not run straight. You are inputting thru trans. control a duplicate response from BOTH pumps. I dont feel the diagnosis is complete. And do not want to spend $3500.00 on one pump. To then find out there are additional problems. Where can I find Field applied diagnostic testing procedure?
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Answered in 2 minutes by:
8/12/2013
Mechanic: catmastertech, Technician replied 9 years ago
catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 3,996
Experience: Field service technician for CAT 19 years.
Verified

catmastertech :

The motors should not turn when the lever is in neutral.

catmastertech :

His call for the LH pump stuck sounds correct.

catmastertech :

The first test I would perform is to see if pump can be set to neutral. If not, an internal problem is causing the pump to stick in the forward position.

catmastertech :

Were any fault codes present related to this issue?

catmastertech :

Here is the procedure to perform the neutral adjustments.

catmastertech :

click the above line to see the test.

catmastertech :

ECM is most likely locking the speed control since the speeds are not match to input of the joystick. I am surprised it is not locking the brake. Needle may move on the dash but, track speed will not change under this derate condition.

catmastertech :

All calibrations must be done with the service software CAT ET that the dealer has.

Customer:

So if ECM detects a mismatch. It goes to derate? If I select REV. it does immediately lock the park brake. But in FWD. the R.H. motor will drive slowly no matter speed position.

catmastertech :

I am guessing (since I did not see the testing) when you select reverse, the servo has just enough control to bring the pump swash plate back to neutral and make some reverse output.


So, you are some what correct to say the pump is not stuck. However, something is not allowing the pump to stay in neutral.

Customer:

Can the servo be removed from the pump. No matter the position of the swashplate? I would like to start by checking if the servo is stuck. Will the swashplate neutral after servo is removed?

catmastertech :

No servo is built into the pump.

catmastertech :

The servo is physically attached to the swash plate.

catmastertech :

The electric solenoids are controlling the servo. If this is stuck open, you could get pressure to one side when it should be in neutral.

Customer:

OK, Thanks for your help. I will remove the pump and take to hyd. shop for service/repair.

catmastertech :

A simple test may be to swap the solenoids.

catmastertech :

This would allow you to know that they are not causing the failure to neutralize.

catmastertech :

Remove the coils and then change the stem of the solenoid. Inspect for trash or blown seals in the end of the stem.

catmastertech :

If the problem moves to the other side, then the solenoid is the fault.

Customer:

The FWD. solenoid was removed and L.H. pump runs the same no matter what. As soon as park brake is released. It does not change. I was just concerned WHY when you input a fwd full speed command. The R.H. track did not respond resulting in a straight line travel.

catmastertech :

You would need to know the servo inputs to see if it is responding to ecm output. Monitoring servo pressure should be equal in forward to produce equal travel. Since you are already starting out with a mismatch of speed, the ecm will prevent motor speed changing.

catmastertech :

Travel speed is both motor servo and pump servo controls to make highest speed.

Customer:

THANKS.

catmastertech :

The ECM will control the speed of each track independently in order to achieve the desired speed and steering. The advantages of the feature for the desired speed and steering are listed.



  • Precise motor speed control

  • Repeatable speed and steering control

  • Improved straight tracking capability

  • Consistent tracking and steering control in all speed ranges


The feature for the desired speed and steering will help compensate for changes in the machine such as the oil temperature and component wear. The ECM uses the input from the operator from the following items in order to determine the desired speed and steering:



  • The joystick FNR

  • The joystick steering

  • The joystick buttons for acceleration and for deceleration

  • The decelerator pedal

  • The service brake pedal

  • The parking brake switch


The desired speed can be modified. The modification is based on the conditions of the underspeed condition, the overspeed condition, and the fault condition. The ECM modulates the current to the pump and motor solenoids. The modulation is based on the feedback from the motor speed sensors. The modulation is used in order to achieve the desired speed on each track.


Note: The parameters of the ECM are programmable through the Caterpillar Electronic Technician. Refer to Testing and Adjusting, RENR5539, "Position Sensor (Forward/Neutral/Reverse) of Joystick Control - Calibrate".

catmastertech :

This may make more sense. Look at the pump speed as part of the engine throttle and the motor speed as part of the thumb rocker on the direction lever.

catmastertech :

BUT, when the ecm see a fault, all controls are locked down to a minimum.

catmastertech :

You have a pump this is not under the ecm control and cannot be controlled so, the ecm only allows minimum output.

Customer:

I believe you have given me the information I need to proceed. Thanks Again for the help. You put it in terms that made sense. The Cat dealer did not go to those measures. Thats why I am here. Dont want to throw money at a gremlin w/o a FULL diagnosis. Until next time Thanks.

catmastertech :

Your welcome.

catmastertech :

If you still fell uncomfortable about the diagnosis, ask for the machine to be checked again. I am sure the dealer would like to keep you as a customer than loose you.

catmastertech :

I would recommend the tractor be sent to the shop if they have a Master Tech there that has some experience on this machine.

catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 3,996
Experience: Field service technician for CAT 19 years.
Verified
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Category: Construction and Road Equipment
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