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Old 08-05-2019, 09:46 AM   #1
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Hydraboost Noise

Greetings all - I put a hydra boost back into a truck that I've had in the truck before, where it worked great and silently. Then the unit came off, sat on the shelf for 10 years, and then I went and put it back on (long story).

This second time, though, it's noisy like I cannot bleed it. It's a tiny bit noisy just sitting at idle, and then if you turn the wheel or hit the brake it starts to groan.

I've done the bleeding procedure (including the one from Ford, which includes the brake pedal step) many times now and no improvement.

The shop thinks the flow is too high and is going to install a restrictor. But should I have any hope of that working?

I'm wondering if there's too much flow to the return now that there are parallel return paths and that's unloading the relief valve? Kinda grasping for theories...

Any good theory welcome!
1970 GMC Sierra Grande Custom Camper - Built, not Bought
1969 Pontiac 2+2 427/390 4-speed Coupe
1969 Pontiac 2+2 427/390 4-speed Convertible
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Old 08-05-2019, 10:27 AM   #2
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Re: Hydraboost Noise

How did you bleed it? Likely just not fully bled yet, despite best efforts. I'm bleeding mine, engine off, by turning the wheel lock to lock 5 times, then pressing on the brake 3 times, checking the fluid, and repeating. I'm 21 times in and it's still accepting new fluid. I've read it can take anywhere from 20-80 times to truly get all the air out.

Last edited by siggyfreud; 08-05-2019 at 11:43 AM.
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Old 08-05-2019, 05:37 PM   #3
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Re: Hydraboost Noise

I would try to tighten the belt real tight, just to see if it stops. Every time I have a groan, it's caused by steering and it's the belt. I don't think you have too much pressure. Pump needs it's full dose of horsepower when you steer, the accumulator helps in breaking, so I think it's why I never get groaning on breaking, just steering.

White K20
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Old 08-05-2019, 08:29 PM   #4
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Re: Hydraboost Noise

10 years on a shelf means the seals have dried up and its bypassing causing the groaning noise....

Put a kit thru it and it will be good....

You can get a kit from

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1974 C-10 Longbed
2001 GMC Sierra
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Old 08-17-2019, 02:39 PM   #5
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Re: Hydraboost Noise

I have a similar problem my daily driver. Stepping in the brake to put it in gear is soft and groaning, especially after sitting in the sun all day. Not as bad first thing in the morning. Can’t tell if it’s the pump or hydraboost.
'72 K5, known as 'the Fox.'
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