TROUBLESHOOTING POWER STEERING MALADIES
No one thinks much about a truck’s power steering system until something goes wrong. Then it becomes mighty important. If the steering doesn’t work, the truck can’t move.
• Hard steering — Can be intermittent, or more obvious, during cold weather, fast turning or when starting out under cold temps. If, for instance, hard steering occurs during cold weather (’tis the season!), TRW’s chart immediately suggests that the steering pump’s vanes are sticking, and refers to “Comment A” on the next page; this further explains that this is a temporary condition that revving the engine a bit will cure.
If hard steering happens while the driver’s trying to spin the wheel fast, one of seven things could be wrong. These range from binding at the input side of the steering gear to internal fluid leakage. In each case, you are referred to one or more numbered “tests,” found elsewhere in the booklet and manual, which you can follow in your diagnosis and repairs.
• Reduced wheelcut — If the truck can’t make it through what should be a routine tight turn, the problem could be with the wheel stops, or with misadjusted pitman arm, draglink or poppets.
• Steering wheel kick — Drivers are sure to complain about this. It can be traced to air in the system, mechanical looseness or low pump flow. One other cause can be badly set up linkage geometry, which is something the truck builder should attend to.
• Binding/darting/oversteer — Disconcerting to the driver and something interdependent on a number of variables. If, for instance, cyclic binding can be felt at the steering wheel and it happens once per revolution, the chart says friction, eccentricity or interference are probably to blame. If it happens other than once per revolution, U-joints in the steering column are at too high an angle or need to be lubed.
On the other hand, if cyclic binding cannot be felt at the steering wheel, then seven more things can be at fault. These range from improperly adjusted steering gear to bad kingpins. One of seven tests needs to be done, depending on what you find out as you proceed. TRW engineers have designed 29 separate tests, each appropriate for one or more complaints.
• Directional pull — Hang onto the wheel as you check to see if it happens during braking (which points to brake balance or adjustment, or a steering arm of improper length), or during acceleration (which will lead you in seven other directions, from improper pressure in the steer-axle tires to unbalanced steering gear).
• Road wander/loose steering — Could be the fifth wheel, axle or steering alignment, or several other things.
• Non-recovery — Eleven different causes are possible, the chart says. For instance, interference between the steering gear and the frame, a sticking control valve in the gear, insufficient slip joint travel and excessive pump flow. As you’d expect, some things can cause a number of conditions and complaints.
• Shimmy — Only one of the four possible causes is limited to the power steering system (air present). The others (tire, wheel or brake imbalance or runout, vehicle alignment, and looseness in mechanical systems) can usually be found elsewhere on the vehicle.
• Noise — Tune your ears, because the “squeal” or “click” might or might not be a change from normal sound. If it’s “normal,” there can be four sources (not to worry). If it’s not normal, there can be five causes, ranging from low fluid level to loose components (check ’em out).
• External leakage — The source of the leak may be obvious. If not, check fittings; hoses; the pump, reservoir or cooler; or steering gear. The chart for this condition lists several items under each cause.
Chart Your Way to Easy Steering is available by writing TRW Commercial Steering Division, 800 Heath St., Lafayette, IN 47904, or call (317) 424-5377. Need quick help? Call the emergency road service hotline: (800) TRW-0899.
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