Section 2  - Frame

pressure allows the piston spring to force the piston outward, creating a partial vacuum behind the piston. The partial vacuum causes the intake valve under the head of the piston to open, permit­ting the fluid to flow under the piston head and fill the piston chamber, Fig. 7.
parallel cylinder type. Fig. 9 is a cross section view of this type unit.
Fig. 9—Cross-Section of Parallel Double-Acting Shock Absorber Action
Fig. 7—Shock Absorber Action When Car Strikes a Bump
As the wheels pass over the bump, the car springs rebound and the car frame moves upward, carrying the shock absorber with it. This causes the shock absorber arm to move downward, apply­ing cam pressure on the piston. The cam forces the piston into the cylinder, closing the intake valve. The oil, trapped in the cylinder, forces the
Inside the body and pressed on the camshaft is a double cam, one end of which bears on one piston during compression, and the opposite end on the other piston during rebound. A return spring is provided under each piston to keep the latter firmly against the cams. An intake valve is pro­vided in each piston whose function is to permit fluid to be replenished when lost by piston leakage as the cylinders are filled under pressure from valve discharge of the opposite cylinder. The fluid reser­voir is in the area around the cam.
The two cylinders are identical and the fluid discharge takes place from one cylinder to the other under operating conditions through the relief valves located in the drilled passageways in the shock absorber body. One of the relief valves con­trols the rebound resistance while the other controls the compression resistance. Both of these valves may be reached after removing the valve plugs or nuts. Removing the filler plug permits filling or adding fluid.
Fig. 8—Shock Absorber Action in Controlling Rebound of Car
relief valve off its seat and passes through a re­stricted orifice into the reservoir. This action, Fig. 8, slows up the rebound of the car springs.
The type single-acting shock absorber shown in Fig. 6, with a separately mounted intake valve and relief valve, is used on the front and rear of the 1/2, 3/4 and 3/4-ton special and on the front only of the 3/4-ton long Wheelbase panel truck.
The double-acting shock absorbers used on the front and rear of passenger cars are known as the
Fig. 10—Passenger Car Front Shock Absorber Mounting





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