Chatter after PS pump replacement.

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Jan 13, 2006
Just replaced a leaking PS pump on an 2004 STi for a friend. Followed the book to the letter, including the priming and air purging.
While rotating the wheels to the left with the car on the ground, it has a bad throbbing chatter at idle, like it is stuttering. It is not noticeable while driving it. The pump is quiet, and it is not foaming or bubbling in the remote mounted tank. I spent about 10 min rotating the steering wheel from far left to right purging the air.
Fluid is OEM Subaru. The reservoir has been vacuumed empty, re-filled with fluid and run for several minutes while rotating the wheels several times. The fluid looks perfectly clean.

Any ideas? I am hoping that there is just some residual air in the pump.
check your PS pump belt for proper tension. Too loose of a belt will cause it to chatter (squeal) when you are doing the lock -to-lock turns.
Both belts were replaced and set to the factory manual specs of 8-9mm deflection.
There is no squeal, and it only does it on turning the wheel to the left, for the last 25% travel.
It sounds like you still have air in the rack, and that can be hard to get out. I know they have a vacuum unit you can put on the power steering pump reservoir, but that does not even always get it out. If it is not too bad, just driving it may work this out.
That is what I think it is, and I told him to drive it, keep an eye on the fluid and let me know if it is still doing it in a few days.
Yeah - drive it at this point, and keep an eye on the level.
If it's not better after a week or so, the pump is bad. The rack is probably fine since it had no problems before. Is it a rebuilt pump?
Brand new OEM pump from the dealer. ( $$$ OUCH!! )
I just got a text from the cars owner, and he is noticing nothing abnormal.
If I remember right, the procedure for bleeding the PS system on the Grand Prix was to lift the front of the car off the ground and turn the wheel lock to lock a number of times with the engine off. Could be wrong...
Jack the car up (front wheels off ground) loosen or remove p/s pump cap. Start car and do 10-15 lock to lock turns checking fluid level each 3 complete turns (if oil shoots out put cap on loose). If it still does it take it to the dealer for them to bleed it or give you a replacement pump.

BTW, most Subaru's take ATF in the PS system. What is your speced for?
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