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Discussion Starter · #1 ·
Hey guys, I've got a strange issue with my hydroboost on my 98 GMC k2500, with the 6.5.

So It's got a pretty loud buzzing noise only at idle coming from the brake pedal that starts when its pressed lightly. If I press the brake pedal hard it gets louder. The weird part is turning the steering wheel very slightly makes it start buzzing too, even if I'm not touching the brake pedal. It goes away the second I turn the steering wheel with any force. I never hear the noise when at any rpm above idle.

The brakes and steering work and feel normal, maybe a bit stiff. No leaks anywhere as far as I can tell. I can feel the buzzing when holding the pressure line going into the hydro boost unit.
The fluid was DARK BLACK so I flushed it with new fluid but to no avail...

Guessing my power steering pump or hydro boost unit is toast? Is there a way to tell which one it is?
 

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Sounds to me you may have air in the HB system. Did you bleed it by jacking up the front with stands under it. then with engine at idle to 1200 rpm, cycling the steering wheel R to L many times {Not lock to lock). Also pumping the brake pedal down as far as you can a bunch of times?
 
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Discussion Starter · #3 ·
Sounds to me you may have air in the HB system. Did you bleed it by jacking up the front with stands under it. then with engine at idle to 1200 rpm, cycling the steering wheel R to L many times {Not lock to lock). Also pushing the brake pedal down as far as you can?
Haven't tried it but will give it a shot. But if I've never "opened up" the power steering system how would air get in there? When I flushed it I just did the "turkey baster" method. The buzzing sound started out barely noticeable and over the course of several months has gotten very loud.
 

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Hydraulic fluid is constantly circulating, if there are no requests for boost assist, the pressure remains low, just flow friction.
Steering or brake assist request restricts return flow, creating pressure. Buzzing felt or heard in both steering and brakes is most likely a pump or fluid issue. Open the reservoir cap after running, if there are bubbles or foam, that is a problem.
What fluid did you use? Is contamination possible? Is running level correct?
 

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Discussion Starter · #5 ·
Hydraulic fluid is constantly circulating, if there are no requests for boost assist, the pressure remains low, just flow friction.
Steering or brake assist request restricts return flow, creating pressure. Buzzing felt or heard in both steering and brakes is most likely a pump or fluid issue. Open the reservoir cap after running, if there are bubbles or foam, that is a problem.
What fluid did you use? Is contamination possible? Is running level correct?
Interesting, didn't think of it that way. I've never had a ps pump fail this way, they usually start whining like a bad bearing kinda sound. I used the cheap prestone universal ps fluid. Level is correct. Ill check for bubbles/foam while running.

I've noticed that it seems to get worse when hot.

Would a video of the noise help ? Appreciate everyone's input
 

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No need for the video or sound. Almost certain it is cavitation or foam/bubbles.
I've yet to find any PS pump that wasn't a vane type so they all work the same. Any air entrainment in the fluid causes noise, vibration and harshness as these collapse under pressure, then expand on pressure reduction.
On the reservoir, a heavier weight fluid could cause suction vortex, again producing cavitation.

Had this on an older Honda, drain and replace cured it.
 

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You don't need fancy fluid in tiny bottles for $9. Get several quarts or even a gallon of Dexron III (three; it's OK to use VI (six) but not necessary, and more expensive). You may need to change more than once to dilute the old stuff enough.
 
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^^^ Yup Dex3 is all I have ever used in GM HB systems. Best way to change fluid is do a total flush.
 

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Discussion Starter · #10 ·
Alright I'll do a full drain and flush with dex 3 and let y'all know the results
Well that failed. I did the full flush a week ago, very thoroughly, I pulled the return line and stuck a hose onto it going into a bucket , then started the truck and slowly turned the wheel and pressed the brakes while watching and adding fluid to the reservoir. I did this several times until the fluid coming out was bright red.

It seemed to quiet the noise for a few days but as I'm typing this it's back and just as loud as before.

What should I look at next?
 

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Since the power steering fluid was black, I would suspect the pump has been damaged from heat causing pressure fluctuations which make the noise. You could check running pressure to make sure.
 
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