How to bleed power steering correctly?


New Member
Feb 15, 2021
02 Mustang GT, 155k

TLDR; Perpetual power steering whine when at idle and especially when braking and turning.

Had a bad brake fluid leak that ended with no brake pressure at all. Replaced caliper and line and bled system and that fixed that and the pedal felt normal.

However, as soon as I started it it started making a very loud power steering noise. It gets worse when turning and when braking. These cars have a hydro boost brake booster so the brakes are related to the power steering fluid in ways. I don’t think the steering is any worse now, but the brakes feel different, you go further on the pedal to get the same braking pressure. The noise is really bad even just at idle.

The level of fluid is fine. I attempted to bleed the ps system by turning wheel lock to lock 10 times, and pumping brake 10 times with res open and car off but that didn’t really do anything.

Could it really just be air in the system? Maybe I’m not bleeding it right. And why did it happen after brake replacement?

After attempting to bleed it a second time the noise was a little less worse when idling and turning but still awful when braking. I looked at the reservoir after I started it and turned it off and there were tons of bubbles.

(This is my first post so please let me know if I'm posting in the wrong place)
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Here's the bleeding procedure (taken from another thread I recently read). The system itself is pretty self-bleeding, so it's entirely possible the pump is beginning to fail. BTW, depressing the gas pedal to the floor will also prevent the vehicle from starting (it signals flood clear to the ECU and does not fire the fuel injectors.

1. NOTE: The Hydro-Boost power brake booster is generally self-bleeding, and the following procedure will normally bleed the air from the power brake booster. Normal operation of the vehicle will further remove any additional trapped air. Fill the power steering oil reservoir with MERCON (R) Multi-Purpose ATE XT-2-QDX or MERCON (R) equivalent.

2. Remove the Powertrain Control Module (PCM) fuse to prevent the engine from starting.

3. Crank the engine for several seconds.

4. Check the fluid level in the power steering oil reservoir and add if necessary. Install the Powertrain Control Module (PCM) fuse.

5. Start the engine.

6. With the engine running, turn the steering wheel from stop to stop twice. Turn the engine off.

7. Depress the brake pedal several times to discharge the accumulator.

8. Repeat Steps 5 and 6.

9. If foaming occurs, stop the engine and allow the foam to dissipate.

10. Repeat Steps 5 and 6 as required, until all the air is removed from the system (when the foaming stops).
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If and when you stop the engine get ready for a messy fluid bath. I do not do that. Leave it running and wait for the bubbles to go away. Then slowly turn the steering wheel. Observe the fluid return to the reservoir for bubbles as you approach one steering stop. Time is your friend. I wait for all the bubbles to subside before moving toward the other steering stop. A few of these and you are done with no whine if you got a good rebuild. I prefer ew C2 pumps from Ford for about 325 if you want no further trouble. I used to rebuild these pumps under warranty Fairly easy to replace the vane ad rotor and both end plates. If you go that route make sure and bench test the pump because it is easy to get the new parts installed incorrectly and it will not pump. The book has fairly flakey pictures to reassemble the pump and the new rotor and end plate parts do not match the pictures of the old parts. A true hold your mouth right job if the vane and rotor comes apart on you
I swapped the steering rack on one of my 96’s two weeks ago and basically did what was posted above. Only difference is my car was on jackstands so the tires were not on the ground or on the car for that matter. It basically self bled itself in ~5 min or less following the instructions.

Something does not sound right to me in your situation. I would double check everything. Sorry I can be of more help.
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When I replace a power steering part I refill it with fluid and then loosen the belt. This allows me to spin the pump pulley several revolutions while watching the fluid for bubbles. I quit when I am satisfied there are no more bubbles coming back to the pump. This is real helpful when replacing long power steering hoses like Taurus or any vehicle with a cooler. Air ratchet with the appropriate bolt in the shaft makes it easier