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Discussion Starter #1
While attempting to bleed the power steering system I am getting a distinct hissing sound when the wheel is in full lock and it will continue to hiss as long as I am holding at lock. Anything less than full lock and the hiss goes away.

Some Background: Had leaking hoses and replaced (Reservoir to pump, Cooling coil to reservoir, and Box to cooling coil). I also replaced the reservoir and banjo bolt and two washers on the Box to cooling coil hose.

I am not having any fluid leaks and pump is fairly quiet. It is hard to pinpoint where the hiss is coming from exactly but it is loud enough that I think I should be able to feel air coming out but have not been able to locate it yet. While driving the car I am still getting assisted steering but it seems like there may still be air in the system. It may also be worth noting that even after removing 3 of the 4 power steering hoses I only had to use less than a full quart of fluid total to fill the system up even after my attempted bleed. Any ideas?
 

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When I did my PS hoses and reservoir a month or so ago I ended up cracking the stupid cooling coil somewhere near the fittings because the coil-reservoir and box-coil hoses were on so tight. No hissing but the plastic holder behind the radiator kept getting wet with ATF. Replaced it and all is well.

I also didn't know that bleeding was necessary at first so kept starting the car before turning wheels lock to lock a bunch of times up on the jack stands. If you do that, you will really quickly know if you have air in the system because the pump will make a terrible racket and your PS/ATF fluid will turn into foamy bubble gum for about 15 minutes until the air settles out. I think if you have any air getting in to the system the same thing would happen to you.
 

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Discussion Starter #3
I was pretty careful with the cooling coil so I don't think I cracked it.

I did get bubbles from the first few turns of the wheel during the bleeding but none since then. The hissing really sounds like there is air coming from somewhere and only at full lock.

One other thing I noticed was after replacing the #8 hose from the steering box to the cooling coil (32411094205) the replacement hose is a lot looser where it attaches to the cooling coil than it was with the original hose. This is a genuine BMW hose with genuine BMW o-rings attaching to a genuine BMW cooling coil. I cannot tell if the hiss is coming from this area but the hose is so much looser that it seems like BMW may have updated this part to not fit so tightly in the coil. I'm not sure if anyone has had this experience as well?
 

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its normal, any hydraulic steering is gonna make noise once it hits full lock. i did not have luck with bmw oe seal, they kept weeping so i just used some thicker universal nitrile seals.
 
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