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Vacuum Bleeding

After replacing a rack & pinion or power steering pump, and proper flushing & bleeding processes are performed, air may remain trapped in the system; this is particularly true on Chrysler Minivan and Ford applications. Hydraulic noise, groaning or whining, will plague the installer until the trapped air is purged from the system, and using vacuum is the best and easiest way to pull these small air bubbles out.

Vacuum Bleeder Tools (Special Service Tools), specific to O.E. applications can be found through Tech Service Bulletins on Alldata or Mitchells. However, many aftermarket products are available (see Figure 1 and Figure 2) for a reasonable price. Some models use a reservoir to trap fluid, but this is not necessary to complete the job.


Figure 1


Figure 1

A rubber stopper or plug will be needed to seal off the fill hole of the reservoir. Simply purchase the correctly-sized stopper at your local hardware store. Drill a hole through the center of the stopper and Insert the tubing from the vacuum tool into the stopper (see Figure 3).


Figure 3
For large Ford (C2) pumps, use # 2 or # 3 stopper.
For small (C3) Ford pumps, use # 10 ½.
For Saginaw pumps, use # 7.

Using the vacuum tool, apply 15 inches Hg. to the pump reservoir with the engine idling. Cycle the wheel from lock to lock every 30 seconds for approximately 5 minutes while maintaining 15” of vacuum. After 5 minutes, shut off the engine and check the fluid level, topping it off as necessary. Repeat these steps until air has been removed from the system and the whining or groaning noise is eliminated.

If air continues to enter the system, you may have a defective pressure hose or connection. It is possible for pressure hoses to allow air to be sucked into the system because of the amount of power steering pressure (some applications as high as 2,000 PSI) but not have external leakage. When in doubt, always change the hoses. It is impossible to inspect the internal condition of hoses, so be safe and replace if suspected or if the vehicle has high mileage.

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