2010/03/04 Caterpillar

Articulated Truck:

735 (S/N: B1N1-UP; AWR1-UP)

740 (S/N: AXM1-UP)

740 (S/N: B1P1-UP)

740 EJECTOR (S/N: B1R1-UP; AZZ1-UP)

Service Magazine SEPD0861, 25 October 2006, "Orifices in the Brake Lines Improve the Performance of the Pressure Switches Articulated Trucks". Disregard this article. See the replacement article that follows.

Description of Change: Orifices have been introduced into the lines for the parking brake system and the service brakes system in order to improve the performance of the pressure switches for the low pressure warnings of the brake systems.

Adaptable To: Two orificed elbows have been introduced into the service brake system and the parking brake system on the listed machines. Each of the orificed elbows are made of a 294-2630 Elbow, a 101-4845 Orifice Plug and two 3J-1907 O-Ring Seals .

One of the orificed elbows is installed between the check and pressure reducing valve and the 213-6947 Pressure Switch for the low pressure warning for the service brake system.

One of the orificed elbows is installed between the brake control valve and the 213-6947 Pressure Switch for the low pressure warning for the parking brake system.

The orificed elbows are effective on 735 (S/N: B1N598-UP), 740 (S/N: B1P1468-UP) and 740 EJECTOR (S/N: B1R253-UP).

The orificed elbows are adaptable to all earlier machines that are listed. First, make two orificed elbows for each machine that is being reworked. Refer to "Making of an Orificed Elbow". Then install the two orificed elbows into the systems for the service brakes and the parking brakes. Refer to "Installing the Orificed Elbows into the Brake Lines".

Making of an Orificed Elbow

Make two orificed elbows for each machine that is being reworked. The parts that will be required to rework one machine are given in Table 1.

Table 1

Parts that Are Required to Make a pair of Orificed Elbows
Item	Part Number	Description	Qty
1	294-2630	Elbow	2
2	101-4845	Orifice Plug	2
3	3J-1907	O-Ring Seal	4

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Illustration 1	g01291897

1. Apply a small amount of 185-3996 Thread Lock Compound to the thread of orifice plug (2). Ensure that the thread lock compound does not block the hole of the orifice plug.

2. Install orifice plug (2) into the 1/16" - 27 NPTF threaded hole of elbow (1). Ensure that the orifice plug does not protrude from the elbow and that the hole of the orifice plug is clear.

3. Install O-ring seals (3) onto each end of elbow (1) .

Installing the Orificed Elbows into the Brake Lines

Start By

• Park the machine on a surface that is flat and level.

• Engage the parking brake and block the wheels.

• Install the steering frame locks. Refer to Operation and Maintenance Manual, "Steering Frame Lock".

• Raise the body and install the body prop. Lower the body onto the body prop. (This does not apply to the 740 EJECTOR Articulated Truck.)

• Raise the cab. Refer to Operation and Maintenance Manual, "Cab- Tilt".

• Shut down the engine. Refer to Operation and Maintenance Manual, "Engine Shutdown Control".

• Turn the battery disconnect switch to the OFF position. Refer to Operation and Maintenance Manual, "Battery Disconnect Switch".

Modifying the Check and Pressure Reducing Valve

1. Locate the check and pressure reducing valve that is positioned at the rear of the front frame.

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Illustration 2	g01291904

2. Remove any cable straps that secure harness (4) to pressure switch (6) before disconnecting the harness from the pressure switch.

3. Remove pressure switch (6) from adapter (5) .

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Illustration 3	g01291906

4. Loosen hose (7) at the connector to the check and pressure reducing valve. Reposition the hose in order to provide clearance for the new position for the pressure switch. Refer to Illustration 5. Tighten the connector when the hose is correctly positioned.

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Illustration 4	g01291908

5. Install orificed elbow (8) to adapter (5). Orient the orificed elbow in order to face the direction that is shown in Illustration 4.

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Illustration 5	g01291909

6. Install pressure switch (6) to orificed elbow (8) .

7. Reconnect pressure switch (6) to harness (4). Secure the harness to the surrounding components with a suitable cable strap. Refer to the arrow in Illustration 5.

Modifying the Parking Brake Valve

1. Locate the parking brake valve that is positioned on the inside of the rear frame.

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Illustration 6	g01292130

2. Remove any cable straps that secure harness (10) to pressure switch (9) before disconnecting the harness from the pressure switch.

3. Remove pressure switch (9) from the parking brake valve.

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Illustration 7	g01292131

4. Install orificed elbow (8) to the parking brake valve. Orient the orificed elbow in order to face the direction that is shown in Illustration 7.

5. Install pressure switch (9) to orificed elbow (8) .

6. Reconnect pressure switch (9) to harness (10). Secure the harness to the surrounding components with a suitable cable strap. Refer to the arrow in Illustration 7.

End By

• Turn the battery disconnect switch to the ON position. Refer to Operation and Maintenance Manual, "Battery Disconnect Switch".

• Return the engine shutdown control to the START position. Refer to Operation and Maintenance Manual, "Engine Shutdown Control".

• Lower the cab. Refer to Operation and Maintenance Manual, "Cab- Tilt".

• Start the machine and observe the alert indicator on the dash for the brake oil pressure. Ensure that the alert indicator momentarily illuminates at start-up with all the other alert indicators and ensure that the alert indicator turns off with all the other alert indicators. Refer to Operation and Maintenance Manual, "Monitoring System".

• Raise the body and remove the body prop. Lower the body onto the frame. (This does not apply to the 740 EJECTOR Articulated Truck.)

• Remove the steering frame locks. Refer to Operation and Maintenance Manual, "Steering Frame Lock".

• Remove the blocks from the wheels.