DRUM ASSEM. 7F4047 - Caterpillar

Main Relief Valve
Illustration 1 g00936964
(1) Transmission hydraulic control
(2) Main relief valve
(3) Adjustment screw for main relief valve
Illustration 2 g00908021
Components of the main relief valve
(1) Transmission hydraulic control
(3) Valve adjustment screw
(4) Spring
(5) Spool
(6) Slug chamber
(7) Slug
(8) Drain
(9) Passage to transmission modulating valves
(10) Passage to transmission lube
(11) Drain
(12) Locknut Main relief valve (2) is located in transmission hydraulic control (1). The transmission hydraulic control is mounted on the top of the transmission planetary. The main relief valve maintains system pressure in the controls section of the power train oil pump. This oil is used to control the brakes and the transmission clutches.Some of the oil that flows through the main relief valve supplies the modulating valves for the transmission. The excess oil that passes over the relief valve flows to the transmission and to the bevel and transfer gears for lubrication purposes. Oil from the pump flows into passage (9). Oil in this passage enters a hole in spool (5) and flows through an internal passage in the spool. The pressure of this oil is felt in slug chamber (6). This oil acts on slug (7). Slug (7) cannot move to the right. Therefore, the oil pressure wants to push spool (5) to the left. When the oil pressure in slug chamber (6) exceeds the force of spring (4), the spool moves to the left. This allows some oil to flow through the passage (10), and the oil then becomes transmission lube .Spring (4) has external adjustment screw (3) and locknut (12) which is located on the side of the manifold for the main relief valve. Movement of the adjustment spring changes the pressure setting of the relief valve.
Illustration 3 g00897904
Top view of transmission hydraulic control
(1) Transmission hydraulic control
(2) Main relief valve
(3) Adjustment screw
(A) Drain
(B) Supply
(C) Number 1 clutch
(D) Number 2 clutch
(E) Number 3 clutch
(F) Number 4 clutch
(G) Number 5 clutch
Illustration 4 g01897433
Bottom view of transmission hydraulic control
(F) Number 4 clutch
(G) Number 5 clutch
(E) Number 3 clutch
(C) Number 1 clutch
(D) Number 2 clutch Transmission Modulating Valves
Illustration 5 g00936965
Transmission modulating valves
(F) Clutch 4
(G) Clutch 5
(C) Clutch 1
(D) Clutch 2
(E) Clutch 3
Illustration 6 g00908024
(13) Test port
(14) Ball
(15) Orifice
(16) Valve spool
(17) Spring
(18) Solenoid
(19) Pin
(20) Passage to clutch
(A) Drain
(B) Supply oil from pump The transmission clutches are hydraulically engaged and released by spring tension. There is one modulating valve for each clutch. Solenoid (18) is energized in order to engage the corresponding clutch.The modulating valve allows the respective clutch to fill with oil to a pressure that is determined by the amount of current going to the solenoid. The ECM determines the amount of current that is supplied to the solenoid.The amount of current that is supplied to the solenoid is determined by the response of the machine, which includes the following indicators:
Speed sensors
Gear selection
Oil temperatureAs current is applied to the solenoid, pin (19) extends to the right. The pin moves ball (14) closer to orifice (15). The ball begins to restrict the amount of oil to drain (A). This increases the pressure on the left end of valve spool