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| Illustration 1 | g00423938 |
Steering and Brake Control Valve (The engine is stopped.) (1) Shaft of the parking brake. (2) Lever. (3) Poppet valve. (4) Check valve. (5) Passage. (6) Shaft for left turn. (7) Plunger for left steering clutch. (8) Spool for left steering clutch. (9) Passage to drain. (10) Chamber. (11) Passage. (12) Passage. (13) Passage. (14) Chamber. (15) Passage. (16) Passage. (17) Chamber. (18) Lever for left steering clutch and brake. (19) Chamber. (20) Chamber. (21) Passage. (22) Plunger for left brake. (23) Spool for left brake. (24) Lever for both brakes. (25) Plunger for right brake. (26) Chamber. (27) Spool for right brake. (28) Passage. (29) Lever for right steering clutch and brake. (30) Plunger for right steering clutch. (31) Spool for right steering clutch. (32) Chamber. (33) Chamber. (34) Passage. (35) Passage. (36) Chamber. (37) Passage. (38) Passage. (39) Shaft for right turn. (40) Shaft for foot brake pedal. (A) Shims. (B) Shims. (C) Shims. (D) Shims. | |
The steering and brake control valve is installed on the front of the case. The steering and brake control valve is operated by the linkage that connects the steering levers, the foot brake pedal and the parking brake lever to the steering and brake control valve.
The first movement of a steering lever causes the steering clutch to disengage and the tractor makes a gradual turn. Further movement of the steering lever engages the brake and the tractor makes an acute turn. The foot brake pedal engages both brakes in order to stop the tractor. The parking brake lever engages both brakes in order to prevent the tractor from moving.
Oil flow to the steering and brake control valve comes from the transmission charging section of the oil pump. Part of the oil flows to the priority valve. This oil then flows to the transmission controls. Part of the oil flows to the steering and brake control valve. The oil that flows to the control valve goes in the supply port. This oil then flows to passage (5) , to passage (12) and to passage (34) .
Oil that flows to passage (12) and to passage (34) flows through chamber (14) and through chamber (36) to the steering clutches. When the clutches, the passages and the chambers are full of oil, the pressure in chambers (14) and (36) increases. This oil pressure is sent through passage (15) and through passage (37) to chamber (10) and to chamber (32) . The oil pressure starts to move spool (8) and spool (31) to the left against the spring force. If the oil pressure that is against the spools is equal to the spring force, the spools will allow only enough oil into chambers (14) and (36) in order to make up any leakage. This will also keep a constant pressure on the clutches. The pressure that is on the clutches is approximately 2750 kPa (400 psi). This pressure can be adjusted by adding shims (A) or by removing shims (A) . When the clutch pressure is decreased to 0 kPa (0 psi), the clutches are released by the pressure of the lubrication oil that is around the clutches.
Oil to passage (5) flows through check valve (4) to passage (11) . Passage (11) moves oil to chamber (17) . The oil then flows to chamber (19) and to chamber (33) . Oil through these chambers flows to the brakes. When the brakes, the passages and the chambers are full of oil, the pressure in chamber (19) and in chamber (33) starts to increase. This oil pressure is sent through passage (16) and passage (38) to chamber (20) and to chamber (26) . The oil pressure starts to move spool (23) and (27) to the left against the spring force. If the oil pressure that is against the spools is equal to the spring force, the spools will allow only enough oil into chambers (14) and (36) to make up any leakage. This will also keep a constant pressure on the clutches. The pressure on the brakes is approximately 2750 kPa (400 psi). This pressure can be adjusted by adding shims (B) or by removing shims (B) . As the brake pressure approaches 0 kPa (0 psi), the brakes are applied by spring force.
Gradual Left Turn
(The Steering Clutch Is Not Engaged And The Brake Is Not Engaged.)
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| Illustration 2 | g00423940 |
Steering and Brake Control Valve (Gradual Left Turn) (6) Shaft for left turn. (7) Plunger for left steering clutch. (8) Spool for left steering clutch. (14) Chamber. (18) Lever for left steering clutch. (C) Shims. (A) Supply from pump. (B) Left brake. (D) Right brake. (E) Right clutch. (F) Left clutch. (AA) Pump oil. (BB) Oil for steering clutch pressure. (CC) Brake pressure oil. (LL) Drain oil. | |
When the operator starts to pull the left steering control lever, the linkage turns shaft (6) . Lever (18) is connected to shaft (6) and lever (18) is in contact with plunger (7) . During the first movement of the steering control lever, plunger (7) moves to the left until plunger (7) contacts the spring retainer that is on spool (8) . Further movement of plunger (7) compresses the springs on spool (8) . This starts a modulated reduction in the clutch pressure. As plunger (7) continues to move, the clutch pressure gradually decreases to 0 kPa (0 psi) and the clutch is released. This allows the tractor to make a gradual turn to the left.
Once the clutch pressure reaches 0 kPa (0 psi), plunger (7) comes in contact with spool (8) . Further movement of the plunger moves the spool to the left. This stops the flow of oil to chamber (14) . Chamber (14) opens and clutch oil is allowed to drain.
Sharp Left Turn
(The Steering Clutch Is Not Engaged And The Brake Is Engaged.)
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| Illustration 3 | g00423941 |
Steering and Brake Control Valve (Sharp Left Turn) (18) Lever for left steering clutch and brake. (22) Plunger for left brake. (23) Spool for left brake. (D) Shims. (A) Pump supply. (B) Left brake. (C) Right brake. (E) Right clutch. (F) Left clutch. (AA) Pump oil. (BB) Oil for steering clutch pressure. (CC) Brake pressure oil. (DD) Residual brake pressure oil. (LL) Drain oil. | |
In order to perform a sharp left turn, the operator pulls back the steering control lever all the way. During the first movement of the control lever, the clutch pressure is modulated to 0 kPa (0 psi). (When a gradual left turn is performed, the clutch pressure is modulated in the same way.) As the operator continues to pull the control lever, lever (18) comes in contact with plunger (22) . Plunger (22) then moves to the left until plunger (22) contacts the spring retainer on spool (23) . Further movement of plunger (22) compresses the springs on spool (23) and this starts a modulated reduction in the brake pressure. As plunger (22) continues to move, the brake pressure gradually decreases to approximately 225 kPa (35 psi) and the brake engages. However, the brake does not engage to maximum pressure due to this residual pressure. This results in a sharp left turn of the tractor. The residual pressure is maintained on the brake in order to avoid any harsh brake application during steering. Add shims (D) or remove shims (D) in order to adjust this residual pressure.
Brake Pedal Operation
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| Illustration 4 | g00423942 |
Steering and Brake Control Valve (The Brake Pedal Is Pushed In.) (1) Shaft for parking brake. (2) Lever. (3) Poppet valve. (4) Check valve. (5) Passage. (9) Passage. (11) Passage. (17) Chamber. (19) Chamber. (22) Plunger for left brake. (23) Spool for left brake. (24) Lever for both brakes. (25) Plunger for right brake. (27) Spool for right brake. (33) Chamber. (40) Shaft for foot brake pedal. (A) Pump supply. (B) Left brake. (C) Right brake. (D) Right clutch. (E) Left clutch. (AA) Pump oil. (BB) Oil for steering clutch pressure. (LL) Drain oil. | |
When the operator pushes the foot brake pedal, the linkage turns shaft (40) . Lever (24) is connected to shaft (40) and lever (24) is in contact with plunger (22) and with plunger (25) . Lever (24) moves plunger (22) and plunger (25) to the left until the plungers contact the spring retainers that are on spool (23) and spool (27) .
Further movement of the plungers compresses the springs on the spools and this starts a modulated reduction in the brake pressure. As plunger (22) and plunger (25) continue to move, the brake pressure gradually decreases to 0 kPa (0 psi) and the brakes are applied by force. This causes the tractor to stop and the torque converter is placed in a stall condition.
Near the end of the brake pedal travel, plunger (22) and plunger (25) come in contact with spool (23) and spool (27) . This moves the spools to the left, which stops the flow of oil to chamber (19) and chamber (33) . Also, the chambers and the brakes are opened in order to allow draining. This results in maximum brake capacity.
Parking Brake Operation (No Illustration)
When the operator engages the parking brake lever, the linkage turns shaft (1) . Lever (2) is connected to shaft (1) and pushes down poppet valve (3) against check valve (4) . This blocks the flow of oil from passage (5) to passage (11) , chamber (17) and the brakes. Passage (11) , chamber (17) and the brakes open in order to allow draining through passage (9) . With no oil pressure to the brakes, the brakes engage in order to prevent movement of the tractor.