SHIM PACK 1387436 - Caterpillar

Illustration 1 g06268504
(1) Service Brake Control ValveThe service brake control valve is located underneath the front side of the cab.A mechanical link connects the two brake pedals to each other. When a brake pedal is depressed, a lever and cam assembly actuates the service brake control valve. The control valve is a fully split modulating valve with two independent output pressures.
Illustration 2 g03369959
Service Brake Control Valve
(J) Outlet to rear service brakes
(U) Outlet to front service brakes
(M) Supply from accumulator for the rear service brakes
(X) Supply from accumulator for the front service brakes
Illustration 3 g03369910
View A-A of the Service Brake Control Valve
(B) Piston
(C) Spring
(D) Spring
(E) Retainer
(F) Ball
(G) Spacer
(H) Upper valve spool
(J) Outlet to rear service brakes
(K) Outlet to hydraulic oil
(L) Passage
(M) Supply from accumulator for the rear service brakes
(N) Drain port to tank
(P) Upper valve spool passage
(R) Cavity
(S) Lower valve spool
(T) Plug
(U) Outlet to front service brakes
(V) Passage
(W) Lower valve spool passage
(X) Supply from accumulator for the front service brakes
(Y) Cavity
(Z) SpringThe service brake control valve modulates the flow of pressurized oil between the brake accumulators and the service brakes. The position of either brake pedal causes a specific pressure at the service brakes. As the position of the pedal changes, the pressure at the service brakes also changes.When a brake pedal is depressed, piston (B) applies a force on springs (C) and (D). The force of springs (C) and (D) moves retainer (E) and ball (F). Movement of retainer (E) and ball (F) causes upper valve spool (H) to move away from the seat in spacer (G).The movement of upper valve spool (H) causes the movement of lower valve spool (S) and the compression of spring (Z). When valve spools (H) and (S) move, oil flow through passages (L), (N), and (V) to the hydraulic oil tank is blocked.This action allows pressurized oil from accumulator ports (M) and (X) to flow through passages (L), (P), (V), and (W). The oil then flows through passages (J) and (U) in order to apply the service brakes. At the same time, pressurized oil flows into cavities (R) and (Y), and through passages (P) and (W). The oil pressure at the service brakes has the same pressure as the oil in cavities (R) and (Y).Oil pressure in cavity (Y) and the force of spring (Z) act to balance lower valve spool (S) against the force of the pressure in cavity (R). In the same manner, pressure in cavity (R) creates a force against the bottom of upper valve spool (H). The upper valve spool is balanced by the force of spring (C) at the top of spool (H).The force of springs (C) and (D) is balanced by the force that is applied to the pedal. Upward movement of valve spools (H) and (S) causes accumulator ports (M) and (X) to be covered. The level of pressure in the independent valve sections creates a force of feedback. This action allows the operator to modulate the pressure to the service brakes.Valve spools (H) and (S) balance between