whooshing sound from under the dash when I press on the brakes

[Ontheboulder]

I am getting a whooshing sound from under the dash when I step on the brakes, it goes away after i pump the peddle a few times. Any ideas?? 1987 GMC V2500.All the brakes are new with zero miles on them,new calipers and rear wheel cylinders as well as new master cylinder!

 

[Turbo4whl]

If you have a vacuum brake booster, the diaphragm most likely has a crack in it.

 

[CalSgt]

There should be a foam filter in the vacuum booster around the brake pedal rod where it mates to the firewall. I think you should be able to see it with a flashlight from under the dash. If it’s missing that can happen. The one in my factory booster looked like rotten seat cushion foam which crumbled and disintegrated when I removed it.

Did you replace the booster? I’ve read a bunch of customer reviews on refurbished boosters missing the plastic boot that seals to the firewall. I could see them forgetting that part too.

 

[Ontheboulder]

There should be a foam filter in the vacuum booster around the brake pedal rod where it mates to the firewall. I think you should be able to see it with a flashlight from under the dash. If it’s missing that can happen. The one in my factory booster looked like rotten seat cushion foam which crumbled and disintegrated when I removed it.

Did you replace the booster? I’ve read a bunch of customer reviews on refurbished boosters missing the plastic boot that seals to the firewall. I could see them forgetting that part too.

thanks! the booster is original I think! why would the noise go away after a few pumps on the pedal ??

 

[Radiohead]

The seal gets exercised and starts to work?

 

[Craig 85]

Another possibility is there is a valve under the dash near the brake pedal if you have cruise control. This hose hose hooks up to the cruise control pod (between the TBI and power brake booster here) and runs through the firewall to the cruise cut off switch.

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[Ontheboulder]

Another possibility is there is a valve under the dash near the brake pedal if you have cruise control. This hose hose hooks up to the cruise control pod (between the TBI and power brake booster here) and runs through the firewall to the cruise cut off switch.

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Thanks!! I bet that is it, cause I was knee deep under the dash last year,never noticed anything

 

[Ontheboulder]

Thanks!! I bet that is it, cause I was knee deep under the dash last year,never noticed anything

Thanks for the picture, mine has 2 vac lines 1 big and 1 small which goes to the vac ball and the big one goes inside the cab. My cruise is disconnected so no worries on it working but just want the brakes to be good.I did hit the brake pedal hard a few times thinking of the proportioning valve,now the pedal seems much firmer and no more whooshing noise.