988G Stall Speeds Require Careful Attention to Operating Parameters Caterpillar

988G Stall Speeds Require Careful Attention to Operating Parameters

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988G Stall Speeds Require Careful Attention to Operating Parameters

CONFIDENTIAL TIBU3437-01

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TECHNICAL INFORMATION BULLETIN	January 15, 2003
WHEEL LOADERS	988G (2TW1-Up, BNH1-Up)
	Component Code: 3101-V8, 5084- V8, 5070-V8

SUBJECT: 988G STALL SPEED TESTS REQUIRE CAREFUL ATTENTION TO OPERATING PARAMETERS

PROBLEM: Inaccurate single (torque converter) stall and double (torque converter and implement pump) stall speeds can be produced if the test procedures are not followed. The controls and position feedback of the linkage require specific settings to accurately determine stall speeds. The tests published in the 988G Hydraulic & Power Train Troubleshooting Testing and Adjusting publications will soon be revised to clarify these procedures.

SOLUTION: The following table describes the four stall speed tests and explains the test parameters:

Note: Stall speed tests should be performed at high idle with the parking brake on, the service brake pedal (right brake pedal) depressed and the transmission & hydraulic oils at normal operating temperatures. The bucket should be flat on the ground before starting the tests. To engage the transmission with the parking brake on in first or second gear, shift the transmission into the FORWARD position then to NEUTRAL and then back to FORWARD.

The variable fan pump should also be run at a known load in order to have consistent stall speed measurement. This can be accomplished by plugging the signal line for the fan pump. This will cause full displacement of the fan pump. Use the following procedure in order to plug the signal line.

1) Turn the engine start switch into the off position. Release the hydraulic system oil pressure. For more information on releasing the hydraulic system oil pressure, refer to Testing and Adjusting- "System Pressure ? Release" for the machine that is being serviced.

Typical example of a signal line connected to a pump control valve

2) Disconnect the signal line from the pump control valve for the hydraulic fan pump.

3) Install a 6V-9828 Cap and a 6V-9507 Face Seal Plug onto the fitting on the control valve. This will cause the pump to operate at maximum pressure and maximum flow.

Stall speeds can be read from the tachometer gauge or from the display window on the monitoring system (with the digital tachometer, operator mode 3, selected) after the above conditions are met and the engine rpm has stabilized.

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TEST	NAME	GEAR	IMPLEMENT HYDRAULIIC	RIMPULL SELECTION CONTROL	LOOSE MATERIAL CONTROL	ENGINE SPEED RPM	COMMENTS
1	Torque Converter Single Stall	4F	Idle/Hold-No Load on Hydraulic	N/A (2)	N/A (3)	2010 +/- 35	Torque converter single stall speeds for 2^nd, 3^rd, 4^th gear should be equal.
2	Torque Converter Double Stall (Using Implement Hydraulics)	4F	Relief- Hydraulic Pressure Achieved by Powering Down Boom Without Going Into Float. (4)	N/A (2)	N/A (3)	1535 +/- 115	Torque converter double stall speeds for 2^nd, 3^rd, and 4^th gear should be equal.
3	Torque Converter Single Stall w/PTS (1)	1F	Idle/Hold-No Load on Hydraulics	Maximum	Off (2)	1900 +/-30	Engine speed is reduced in 1F when "Dig Trigger" (PTS) is active
4	Torque Converter Double Stall (Using Implement Hydraulics) with PTS (1)	1F	Relief-Hydraulic Pressure Achieved by Powering Down Boom Without Going Into Float.	Maximum	Off (3)	1750 +/- 50	Implement Pump is destroked in 1F when "Dig Trigger" (PTS) is active

Powertrain Torque Strategy (PTS) adjusts the operating conditions of the machine when "Dig Trigger" mode of operation is active. In this mode, the maximum engine speed is reduced to 1900 rpm and the implement pump flow is reduced. "Dig Trigger" is active when the machine is in 1F and traveling less than 1.74 mph with the boom position below a horizontal orientation.

The machine will remain at maximum rimpull when the transmission is not in first gear.

Loose Material Mode keeps the hydraulic pump from destroking during a load cycle (i.e. when "Dig Trigger" (PTS) mode is active).

Hydraulic relief pressure can also be achieved by raising boom to full lift position, returning control lever to the HOLD position and then returning and holding the lift control lever in the FULL LIFT position. This second command to FULL LIFT after the boom is in the full lift position avoids a cylinder snubbing strategy, which would otherwise prevent the circuit from generating maximum relief pressure. This however prevents PTS from activating and cannot be used for tests requiring PTS to be active. NOTE: Full implement hydraulic relief cannot be achieved using the tilt circuit as the spool in the main control valve shifts to partially open center at the extreme bucket positions. This reduces the flow and pressure to the tilt cylinder as the bucket hits the travel stops.

NOTICE: To make sure that the transmission oil does not overheat, do not keep the torque converter in a stall condition for more than 30 seconds. After a torque converter stall test, reduce engine speed to low idle, move the transmission control to neutral, and increase the engine speed to approximately 1500 rpm to cool the oil.