2011/03/29 Caterpillar

Wheel Tractor-Scraper:

621G (S/N: DBB1-UP; CEN1-UP)

623G (S/N: DBC1-UP; CES1-UP)

627G (S/N: DBD1-UP; CEX1-UP)

631G (S/N: DFA1-UP; CLR1-UP)

637G (S/N: CEH1-UP; DFJ1-UP)

657E (S/N: 5YR1-UP; 6TR1-UP)

657G (S/N: W1B1-UP; W1C1-UP; A4G1-UP)

ReferenceRefer to the steering system Testing and Adjusting for information on adjusting the pilot pressure.

Description of Change: There is a new check valve that is being used on certain Wheel Tractor-Scrapers. The new check valve will improve rough steering and erratic steering.

Adaptable To: The new 308-9433 Check Valve Gp replaces the previous 9T-6005 Check Valve Gp. This change is adaptable to the following machines:

• 621G (S/N: CEN1-UP; DBB1-UP)

• 623G (S/N: CES1-UP; DBC1-UP)

• 627G (S/N: CEX1-UP; DBD1-UP)

• 631G (S/N: CLR1-UP; DFA1-UP)

• 637G (S/N: CEH1-UP; DFJ1-UP)

• 657E (S/N: 5YR1-UP; 6TR1-UP)

• 657G (S/N: A4G1-UP; W1B1-UP; W1C1-UP)

Illustration 1	g01446180

308-9433 Check Valve Gp (1) is mounted to the Hand Metering Unit (HMU) under the cab. After the check valve gp (1) is installed, the steering pilot pressure will need to be checked in the steering control valve. The steering pilot pressure should be 380 ± 69 kPa (55 ± 10 psi).