Power Steering Failures

Power steering loss can be attributed to many causes, including those indirectly related to the steering system. For troubleshooting tips, read on.

When a power steering failure occurs, the ability to steer the vehicle remains, but the effort to steer it increases dramatically. For our readers over 50-years-old, you probably still remember manual steering. For those of you who are younger, power steering—like other options such as power brakes and air conditioning—is taken for granted. You probably don’t recall a car without it.

Power steering loss can be attributed to many causes, including those not related to the steering system. For instance, if the serpentine drive belt fails, the power steering pump is rendered inoperable and power assist is lost. On the other extreme, if the pump fails, power assist is lost. We’re going to discuss power steering in general, and failures, in particular.

POWER STEERING BASICS

Before we get into diagnosing power steering problems, let’s quickly review the basics of how power rack & pinion 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.

The power assist is provided by a belt-driven, rotary, constant displacement, vane-type pump. A typical power steering pump, such as that used on the 3.3L and 3.8L V-6, is shown in Figure 1. 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 one direction to steer the vehicle.

Modern power steering pumps usually do not have an integral fluid reservoir. The fluid reservoir is in an easy-to-reach location and connected to the pump with high pressure hoses. This allows the fluid level to be easily checked. Also, fluid can be added, as needed, without much difficulty.

DIAGNOSIS AND TESTING

When a power steering problem occurs, defined as hard steering, one of three conditions has occurred. First, as mentioned earlier, the drive belt has broken, or is covered with oil, preventing the pump from rotating. The net result is the lack of pressurized fluid to provide power assist. This condition is pretty easy to diagnose and can be done visually.

The second condition that will cause hard steering is a fluid leak. A leak itself won’t necessarily cause hard steering, but if enough fluid leaks from the system, or the leak occurs within the steering gear, steering effort will increase.

A very common location for a fluid leak is one of the high pressure hoses. Check the hoses at each compression fitting where the metal tube is connected to the flexible hose. Such a leak should be easy to find and will leave power steering fluid stains on the ground.

An internal leak within the steering gear is harder to find. In the early days of rack & pinion steering, it was not uncommon for the spool valve seals to wear grooves into the housing. When the steering gear was cold upon start-up, fluid would bypass the seals, causing a noticeable reduction in power assist. After operating temperature was reached, the seals would expand and seal as designed and provide the required power assist.

Nowadays, on occasion, the seals at either end of the rack will deteriorate and fail, causing fluid to leak. Over time, enough fluid can leak out of the steering gear to reduce the power assist. Quite often, though, there will be no sign of fluid on the ground. Where does the fluid go? Well, it accumulates in the bellows, or protective boots, on the ends of the rack. In extreme cases, the boot will expand and look like a small football.

If you suspect an internal leak such as this, simply squeeze the bellows. If you hear a squishing sound, that’s power steering fluid that has leaked past the rack seal. Unfortunately, rack and pinion gears are not serviceable components. The solution to this problem is a replacement steering gear.

The third condition that will cause hard steering is a bad pump. Something inside the pump is preventing the build-up of pressurized fluid. If you have determined that the pump is rotating and there are no fluid leaks anywhere in the steering system, check the pump.

To check the performance of the pump, perform a power steering system flow and pressure 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 not 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 special tool 6826, 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; start the engine.
7. Record the initial pressure reading and flow reading and compare these numbers to the specifications listed in the appropriate service manual. Caution: 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. Completely open the valve on the power steering analyzer; 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 internally and must be replaced.