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Articles and Publications |
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| · Tech Tips · | 07.28.2006 |
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Put the Power back in your Steering
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 Did you know that $60 billion in vehicle maintenance goes unperformed each year? Too often, motorists let small problems become big problems before they do anything about it. Plus, they fail to have regular and adequate vehicle checkups. Also, many systems and components wear gradually over time so worsening performance may go unnoticed. But when the power steering goes, it becomes painfully obvious right away. Driving today’s vehicles without power steering can be a major workout, especially on large vehicles. Very simply, power steering equipped vehicles are not designed to be driven without power assist.
If there is no puddle of power steering fluid on the ground under the vehicle (an obvious sign that a power steering hose has burst), what causes a power steering system to fail? We’ll find out. Also, we’ll review some specific power steering system problems that have been addressed in DaimlerChrysler Technical Service Bulletins (TSBs).
Power Steering Basics
Before we get into diagnosing power steering problems, let’s quickly review the basics of how power steering operates. The rotary motion of turning the steering wheel is converted into linear (side-to-side) motion through the meshing of the helical pinion teeth with the rack teeth within the steering gear. This lateral travel pushes and pulls the tie rods to change the direction of the front wheels on the vehicle (Figure 1 shows a typical power rack and pinion steering gear).
The power assist is provided by a belt-driven, rotary-type pump and is controlled by an open center, rotary-type control valve. It directs pressurized fluid to either side of a piston located on the rack gear inside the steering gear housing.
Rotation of the steering wheel directs more pressurized fluid to one side of the piston than the other. This imbalance in fluid moves the rack gear in.
Diagnosis and Testing
When a problem occurs with the power steering system, it can usually be traced to the pump, the fluid or the power steering hoses. In the early days of power rack and pinion steering, wear problems in the steering gear housing resulting from the seals of the rotary-type control valve were quite common. Improvements in materials and design, however, have eliminated such problems. Nowadays, the types of problems usually encountered are either effort-related or noise-related.
The first step in diagnosing a power steering problem is a thorough visual inspection of the system. As the fluid is the lifeblood of power steering, a loss of fluid, obviously, can reduce the amount of power assist provided. Check the fluid level in the reservoir. If the fluid level is low, look for any signs of fluid leaks, especially at connection points on the pump, steering gear, cooler and reservoir. Also check the supply, pressure and return hoses for any cracks or splits. Finally, check the tension on the power steering pump drive belt.
If the fluid is low but no external leaks can be seen, there might be an internal leak within the steering gear. Although this type of failure is not common, it can occur from time to time. To check for an internal leak, remove the bellows on each end of the steering gear housing. If fluid comes out of the bellows or is found inside the bellows, there is an internal leak. In severe cases, the bellows might even bulge out from the build-up of fluid. Do not attempt to repair this internal leak. Simply replace the entire steering gear.
If the fluid level is adequate and no leaks can be found, the next step is a flow and pressure test. To perform this test, you will need a power steering analyzer, similar to the one shown in Figure 2.
This test will determine if the power steering pump or power steering gear is functioning properly by measuring the flow rate of the power steering pump, as well as the maximum relief pressure. The power steering system flow and pressure test is performed in the following manner:
1. Disconnect the power steering fluid pressure hose from the power steering pump.
2. Connect the adapter fitting, attached to the pressure hose from the inlet (gauge end) of the analyzer, to the pressure fitting on the power steering pump.
Note: adapter fittings are unique to a particular engine; check the appropriate service manual for the vehicle you are repairing.
3. Connect the vehicle power steering fluid pressure hose to the appropriate adapted fitting, which should be installed in the outlet hose of the analyzer.
4. Completely open the power steering analyzer.
5. Start the engine; run the engine at idle until the fluid circulates through the analyzer and hoses and the air is purged from the fluid. Turn the engine off.
6. Check the power steering fluid level. Add fluid as necessary and start the engine.
7. Record the initial pressure reading and flow reading; compare these numbers to the specifications listed in the appropriate service manual.
NOTE: Do not leave the control valve closed for more than five seconds as the pump could be damaged.
8. Close and open the analyzer valve three times. Record the highest pressure indicated each time. All three readings must be within specifications. If any of the readings are above or below specifications, replace the pump.
9. With the valve on the power steering analyzer completely open, turn the steering wheel to the extreme left until the stop in the steering gear is met. Then turn the steering wheel to the extreme right until the stop is met. Record the highest indicated pressure at each stop. Compare the recorded readings to the specifications. If the highest output pressures are not the same, the steering gear is leaking
Specific Power Steering Problems
Several power steering problems have occurred over the last few years that have caught the attention of DaimlerChrysler engineers. As a result, Technical Service Bulletins (TSBs) have been issued to address these problems. Let’s take a look at a couple of these bulletins.
The first TSB deals with momentary loss of power assist when driving in heavy rain and through deep puddles. This problem is specific to Dodge Neons and involves correcting the tension on the power steering accessory drive belt (TSB 07-04-97). If it is determined that this problem does occur under the conditions, the loss of power assist is caused by water intrusion into the accessory drive belt area. Readjust the belt tension to 100 lbs., using a belt tension gauge (refer to Figure 3). Apply torque to the square hole D, then tighten in order, locking bolt A to 20 ft.-lbs., bolt B to 20 ft.-lbs., and pivot bolt C to 40 ft.-lbs. TSB 19-07-99 is applicable to all vehicles and covers a low frequency noise or moan emitted by the steering system during low speed turns and parking maneuvers. Although some noise is normally present during these conditions, this moan reaches an unacceptable level when the power steering fluid is aerated as a result of low fluid level in the reservoir.
To correct this problem, the air entrapped in the power steering fluid must be purged. This can be accomplished either with or without a vacuum pump. The procedure is rather straightforward.
1. Fill the reservoir to the recommended level at ambient temperature with new fluid, leaving the reservoir cap off.
2. Lift the front wheels off the ground to allow the wheels to be turned without friction.
3. Turn the steering wheel lock-to-lock three times.
4. Check the fluid level and add fluid, if required.
B 5. Start the engine.
6. Slowly turn the steering wheel lock-to-lock ten times while maintaining an engine speed of 2000 rpm (+/- 150 rpm).
7. Let the engine idle for three minutes, then shut off the engine.
8. Lower the vehicle.
9. Check the fluid level and add fluid, if required. |
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