Tie-Rod Assemblies Two  tie-rod  assemblies  (fig.  8-19)  are  used  to fasten  the  center  link  to  the  steering  knuckles.  Ball sockets are used on both ends of the tie-rod assembly. An adjustment sleeve connects the inner and outer tie rods. These sleeves are tubular in design and threaded over the inner and outer tie rods. The adjusting sleeves provide  a  location  for  toe  adjustment.  Clamps  and clamp  bolts  are  used  to  secure  the  sleeve.  Some manufacturers require the clamps be placed in a certain position in relation to the tie rod top or front surface to prevent interference with other components. STEERING RATIO One   purpose   of   the   steering   mechanism   is   to provide   mechanical   advantage.   In   a   machine   or mechanical device, it is the ratio of the output force to the  input  force  applied  to  it.  This  means  that  a relativety  small  applied  force  can  produce  a  much greater force at the other end of the device. In   the   steering   system,   the   operator   applies   a relatively small force to the steering wheel. This action results  in  a  much  larger  steering  force  at  the  front wheels. For example, in one steering system, applying 10 pounds to the steering wheel can produce up to 270 pounds at the wheels. This increase in steering force is produced by the steering ratio. The steering ratio is a number of degrees that the steering wheel must be turned to pivot the front wheels 1   degree.   The   higher   the   steering   ratio   (30:1   for example). the easier it is to steer the vehicle, all other things being equal. However, the higher steering ratio, the more the steering wheel has to be turned to achieve steering. With a 30:1 steering ratio, the steering wheel must turn 30 degrees to pivot the front wheels 1 degree. Actual steering ratio varies greatly, depending on the type of vehicle and type of operation. High steering ratios  are  often  catted  stow  steering  because  the steering   wheel   has   to   be   turned   many   degrees   to produce  a  small  steering  effect.  Low  steering  ratios, called fast or quick steering require much less steering wheel  movement  to  produce  the  desired  steering effect. Steering  ratio  is  determined  by  two  factors— steering-linkage ratio and the gear ratio in the steering mechanism. The relative length of the pitman arm and the steering arm determines the steering linkage ratio. The steering arm is bolted to the steering spindle at one end and connected to the steering linkage at the other. When the effective lengths of the pitman arm and the steering arm are equal, the linkage has a ratio of 1:1. If the pitman arm is shorter or longer than the steering arm,   the   ratio   is   less   than   or   more   than   1:1.   For example, the pitman arm is about twice as tong as the steering  arm.  This  means  that  for  every  degree  the pitman  arm  swings,  the  wheels  will  pivot  about  2 degrees. Therefore, the steering linkage ratio is about 1:2. Most  of  the  steering  ratio  is  developed  in  the steering  mechanism.  The  ratio  is  due  to  the  angle  or pitch of the teeth on the worm gear to the angle or pitch on  the  sector  gear.  Steering  ratio  is  also  determined somewhat by the effective length and shape of the teeth on the sector gear. In a rack-and-pinion steering system, the steering ratio  is  determined  largely  by  the  diameter  of  the pinion  gear.  The  smatter  the  pinion,  the  higher  the steering ratio. However, there is a limit to how small the pinion can be made. MANUAL  STEERING  SYSTEMS Manual   steering   is   considered   to   be   entirely adequate  for  smatter  vehicles.  It  is  tight.  fast,  and accurate   in   maintaining   steering   control.   However, larger and heavier engines. greater front overhang on larger  vehicles,  and  a  trend  toward  wide  tread  tires have  increased  the  steering  effort  required.  Steering mechanisms  with  higher  gear  ratios  were  tried,  but dependable  power  steering  systems  were  found  to  be the answer. There are several different types of manual steering systems, which are as follows: Worm  and  sector Worm  and  rotter Cam  and  lever Worm and nut Rack and pinion Worm and Sector In  the  worm  and  sector  steering  gear  (fig.  8-20), the pitman arm shaft carries the sector gear that meshes with the worm gear on the steering gear shaft. Only a sector of gear is used because it turns through an arc of approximately  70  degrees.  The  steering  wheel  turns the worm on the lower end of the steering gear shaft, which rotates the sector and the pitman arm through the use  of  the  shaft.  The  worm  is  assembled  between tapered rotter bearings that take up the thrust and toad. 8-18