Steering: Description and Operation
Power Steering PumpAll cars are fitted with power-assisted rack and pinion steering gear. movement of the rack by the pinion being assisted by hydraulic pressure acting on a piston carried on an extension of the rack
Hydraulic pressure is provided by a vane-type pump with integral reservoir, belt-driven from the engine crankshaft. steering assistance is, therefore available only while the engine is running. A control valve, located between steering column and pinion, directs hydraulic pressure to the appropriate side of the piston when the steering wheel is turned. Flow through the control valve is continuous, and when the car is travelling straight, a low pressure is applied equally to each side of the piston. When the steering wheel is turned, a small torsion bar at the base of the steering column allows it to rotate a few degrees before turning the pinion, if the pinion is restrained by the rack. This rotation is used to open and close ports in the control valve so that not only is the pressure directed to one side of the pistons but also, as the torsion bar is twisted, the pressure is increased from about 2,8 kgf/cm2 (40 psi) to a maximum of up to 84,4 kgf/cm2 (1200 psi), the increase in pressure being proportioned to the twist in the torsion bar, and reducing to a minimum when the load in the torsion bar from the steering wheel becomes zero.
The pressure is prevented from exceeding 84,4 kgf/cm2 (1200 psi) by a flow control valve in the pump which allows some fluid to circulate internally when this pressure is reached.
Two rigid pipes connect the control valve to the rack cylinder, and two hoses run from pump to control valve. A third rigid pipe, pressed into each end fitting of the rack, balances air pressure in the two gaiters as the rack operates
Servicing of the steering gear is confined to grease lubrication of the two outer ball-joints and the rack damper pad, topping-up the reservoir and inspection for fluid leaks, hose condition, and belt wear. When checking fluid level take great care to ensure that no dirt or scraps of cloth can enter the reservoir since if they should reach the control valve the operation of the system can become affected.
Power assisted steering racks are now oil filled by the supplier with Shell Spirax EP 80 oil. This has replaced the Shell Retinax 'A' grease fill. Racks to this condition were introduced on Jaguar production at the from VIN 426768.
It is important that when investigating power steering fluid leakage, this lubricating oil is not confused with the hydraulic fluid, as under normal operating conditions a small amount of the oil will be present in the steering rack gaiters. If any oil is lost from the gaiters, then an equal amount to that lost should be added to the gaiter prior to the refitment of the gaiter clips.
It is not necessary under normal circumstances to add oil to the rack during Service, unless a complete overhaul of the rack is undertaken. The total oil capacity of the steering rack is 0.19 liters.
WARNING: It is absolutely essential that the highest standards of cleanliness are maintained in any operations involving access to components in contact with fluid, since steering assistance can be seriously effected by the presence of dirt in the system.
DATA
To VIN 360145
Castor angle 2 1/4 ± 1/4 positive
Camber angle 1/2° ± 1/4° positive
front wheels to be within 1/4° of each other
From VIN 360146
Castor angle 3 1/2° ± 1/4°positive
Camber angle 1/2° ± 1/4° negative
Number of turns of steering wheel 3.36 lock to lock
Total stroke of rack 156.5 mm (6.16 in)
Axial rack load with feed pressure of 2,11 kgf/cm2 (30 psi) and pump flow of 9,45 liters/min) at 71° C is to be 18,1 kg (40 lb) max, 13,6 kg (30 lb.) min. Rack to traverse at 6 to 10 pinion rev/min in this test.
Front wheel alignment 0 to 3.18 mm (0 to 1/8 in) toe-in.