Hydroboost nightmare!!

Hi friends, I’m new here, so bare with me. I have just completed building a pro touring 69 cougar with 4.6 DOHC out of a 98 LSC mark 8..
I put a hydroboost from an 01 mustang GT in as space is very limited. My issue is, when I apply the brakes, I get a woosh sound, and under light application of brakes, I also get a pulsation in the brake peddle?? When the car is slowing, I can feel the transmission down shifting. Once the car has come to a complete stop, I feel the peddle jump up and down, ah have the whoosh sound continue, but If I lift my foot to the point the brake peddle is barely applied, sound goes away.
So, I have spent hours bleeding the system, (3 times now). I replaced power steering pump, cause had original LSC pump on motor, and figured I may need to replace with pump from hydroboost car, so replaced with rebuilt pump from 98 cobra. Everything else is new, rack, reservoirs, Lines, everything is dry, no leaks. Hydroboost is only thing not rebuilt or new. Do I need to rebuild, replace, or is it some other cause
So I’m hoping someone here can help me out with this pulsing whooshing sound?? I’m lost, out of ideas and don’t know where to turn next.
Some pics included


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Are you running manual or power rack?

Is the noise a buzzing sound that increases under load? Or distinctly a whoosh? Can you take a video and maybe put it on yourtube?

Is the sound/pulsation RPM dependant? In other words, is the reason you hear it at a dead stop because the motor has returned to idle?

If you create excessive load on the PS pump, the pump will make a noise against the pressure relief valve. If you stand hard on the pedal at a stop you may feel this.

Given that you have changed the pump, I’m leaning towards he hudrobooster being the issue unless something is askew with the plumbing of the lines.

Are you running manual steering? If so how did you route the lines?
I have a power rack. Brand new piece.I will try to load a video in the next day or 2 to see if it can help. Included is how I ran my lines. I here the sound from initial application of applying brakes. Once at a complete stop, with light pressure applied to the pedal I would call a pulsating kick back,buy If I apply more pressure to pedal, the kick back stops, but the sound continues. It is a more distinct whoosh sound.
Thank you for the help so far, once I post a video, I will let you know.
Kool Kat


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I have 2 Videos that I will try to Upload. I find that when the car is at a complete stop, and pedal is held down ever so softly, it starts to kick back (pulsate).. I have also come to think that the steering isn’t as easy as I feel it should be for a power system.
Once again, thanks for any help and or suggestions you may have.
That sounds like the pump straining against restriction. Can you do the same and have somone press the pedal while you hold a screwdriver on the pump and see if you can feel a vibration in time with the noise. Given that you've replaced the pump, i would see if any of your fittings are undersized and presenting a flow restriction.