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Thanks to its compact design and relative mechanical simplicity, hydraulic power steering rack and pinions are found in most current passenger vehicles, sport utility and light trucks. Due to the specialized tooling needs, hydraulic power rack and pinion gears are generally supplied to the aftermarket as remanufactured units, in either the long version that include inner tie rod ends (the ones you see most commonly, think Volvos, Nissans, Mercedes, or the short version that does not (ZF rack BMWs, Audis).


Due to the steering racks relative inaccessibility, and the fact that some of the more mechanically inclined customers tend to tackle this job themselves, we tend to recommend the long rack with new (and vital, but I'll get to that later) power steering hoses. In addition, it's important to follow the remanufacturer’s installation procedures regarding the use of application specific fluids and to flush the hydraulic system to remove contaminated fluid.


How does it work?

A power steering rack contains four major components:

  1. The rack gear, the section that is attached to the tie rods and in turn the spindles,
  2. The pinion or steering gear attached to the steering column
  3. The hydraulic assist cylinder attached to the rack gear
  4. The metering valve connecting the steering wheel shaft to the pinion gear.

The metering valve includes a small torsion bar that twists or deflects according to the amount of torque applied to the steering wheel. As the torsion bar does so, the valve allows more fluid pressure to enter the assist cylinder.


Diagnosing a failure of a power steering rack in retrospect is rather simple, I made a point of not mentioning the pump as I want to keep the focus on the gear and rack assembly (also as oddly enough I sell more rack and pinions then I ever sell pumps). The most common of these failures is fluid leakage from the assist cylinder into the bellows. Often times customers will call in claiming there rack bellows appear to be bulging with fluid as if they will burst.

A less common fault and one a bit harder to spot is leakage coming from the metering valve and the housing for the cylinder (usually see fluid begin to drip from the portion of the gear where it meets the column), which can cause a temporary or intermittent loss of steering. Metering valve failure can also cause in some extreme cases, a pull to one side or another.

In either case, when a faulty or defective steering rack is confirmed, the proper steps need to be taken to ensure the replacement does not share the same fate. Though tedious, and time consuming, it is vital and imperative that whenever a replacement rack is installed all the associated lines, hardware, and fluid be changed along with them. You must ensure above all else, that the existing fluid within the system is flushed with manufacturer specific fluid, making sure you rid the system of ALL contaminants before final system pressurization is completed. The number one fault I have seen in most replacements of power steering racks is people thinking this is a simple "unbolt, bolt-on" procedure.

Now, I have never been one for doing the same labor twice, so before I even begin installing the new rack I run at least two bottles of fluid through the pump, reservoir, and lines to ensure they bleed through picking up what contaminants I can. You are basically throwing away this fluid but it definitely pays off dividends later (given the cost of replacement racks, and their hefty core fees, I can live with throwing away two bottles of 20 dollar fluid). After I feel comfortable with the cleanliness of the system I would begin installing a new rack, after of course I purchase new washers for the lines leading to it, or new lines if need be. Then I follow the rigorous procedure of bleeding the system outlined below.

  1. Lift the front end of the vehicle and properly support it on jack stands/lift ensuring the front wheels are off the ground and not supporting weight (I jack the car up fully front and back on cars with four wheel steering, ensuring all four wheels are off the ground).
  2. Drain the power steering fluid, first by disconnecting the low pressure hose at its lowest point on the car and allow as much fluid to seep as possible.
  3. Reconnect that low pressure hose, usually located near the rack leading from the power steering reservoir (but not always the same).
  4. Remove the cap from the power steering reservoir and add the recommend amount of the manufacturer suggested power steering fluid.
  5. Replace the power steering cap and seal the reservoir.
  6. Start the motor and rotate the steering wheels from lock to lock for about 5 minutes or at least 30 lock to lock cycles.
  7. While turning listening for any noise from the pump indicating there is air in the system.
  8. Continue turning until all air is removed from the system and there is no sound emanating from the system.
  9. Turn the car off and allow it sit for at least a few minutes.
  10. Disconnect the low pressure hose and allow that fluid to drain once again.
  11. Reconnect the hose and refill the reservoir to the appropriate level using the manufacturer suggested fluid.
  12. Start the vehicle and repeat step 6 turning lock to lock and "burping" the system of any air.
  13. Turn off the vehicle and let it rest for another few moments.
  14. Repeat the process of draining, filling, turning lock to lock until you have forced 2 quarts of the manufacturer suggested fluid through the system, flushing out any contaminants/old fluid/ debris that may be inside.
  15. Remove both lines leading to and from the steering rack ensuring both line ends stay elevated and do not come into contact with the ground.
  16. Remove old steering rack from vehicle. Following manufacturer recommended procedure.
  17. Install replacement rack and connect lines to rack using new washers, if applicable.
  18. Remove the cap from the power steering reservoir and add the recommend amount of the manufacturer suggested power steering fluid.
  19. Start the motor and rotate the steering wheels from lock to lock for about 5 minutes or at least 30 lock to lock cycles. Turning off motor to add more fluid periodically to refill the system.
  20. Test drive vehicle once lowered to ensure system is operating properly.


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Written by :
Michael Rivera

Mike is a former ASE Certified Technician and has over 10 years experience working on various European makes and models. This FCP veteran has been with us for almost 8 years and has worked very closely with our customers helping with technical advise and service. Mike is our Audi & VW catalog manager and is heading up the build out and restructuring the Audi & VW segments of the FCP Catalog. He can be reached at

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