| Binding Steering Gear |
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| Care should be taken that uneven mounting surfaces are not distorting the steering gear housing. The steering linkage should be able to be turned freely, from lock to lock, with the engine switched off. It is best to rotate the pitman arm, with linkage and column disconnected, by hand if tightness is suspected. In the case of rack and pinion systems both links should be disconnected from the wheels and the column also disconnected. There will be some resistance to movement but operation should be smooth throughout the full cycle. If binding is evident then loosen one of the mounting bolts and check to see if the housing pulls away from the mounting surface. Re-tighten and then check the next bolt. Any low points can be shimmed prior to tightening the bolt. Because of the small clearances used in steering gears any housing distortion will cause binding. |
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| Column Friction or Drag |
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| As mentioned previously, there is no mechanism to self centre a steering gear after turning a comer. The system relies on the self centering force generated by caster. If there is excessive column friction, say in excess if 1.5 - 2 Nm (15 in/lbs), then the valve may be displaced, by column drag, causing a pressure build up which will oppose the self centering force generated by caster. |
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| Column Universal Joint Phasing |
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| Universal joints in columns, if used, can create speed variations in steering shafts. Normally, in drive lines, joints operate at equal angles with the yokes placed in line. This arrangement cancels out speed variations. However, in steering columns universal joints can rarely be set to operate at equal angles. In many cases there are 3 or more u joints all operating at different angles, or worse different compound angles. To reduce speed variations the yoke of u joints are purposely misalignment so that some u joints may cancel, or reduce shaft speed variations. If columns are removed they should be marked before any attempt is made to dismantle them so that factory alignment is maintained. |
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| Figure 6 |
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| Figure 6 demonstrates the effect of universal joint operating angles by plotting the ratio of the velocity fluctuation over 180degree rotation. The operating angle of the universal joint in this illustration is 40deg. Ideally this problem is magnified by the use of a 2nd U joint operating at the opposite angle. However this is almost impossible to achieve in many steering column installations. |
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| Free Play |
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| Steering free play should always be checked with the engine running. There is a degree of lost motion due to the operation of the valve and spring in the steering gear. This lost motion is at it's highest when high steering gear outputs are required, when parking for example. However, on the highway only small amounts of pressure are required and therefore lost motion due to valve movement is minimal. |
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| Pump Belt Tension |
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| Pumps can use considerable power and the correct belt tension is most important. You have often heard belt squeal as slippage occurred when parking a vehicle. If the steering action is "knotty" or jerky when parking then look at the pump pulley while the steering is cycled lock to lock. You will probably see the slippage. |
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| Worn or Seized Links |
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All steering links should be free to move and not have any free play. Split seating boots are a good indicator that a ball joint may be worn or seized. Worn ball joints can cause wheel shimmy and seized or tight joints can promote steering darting and a reluctance to self centre. |
