i just finally got my car tuned with my turbo on, and after letting off after boost and hit the brakes my brake pedal is super hard and i really cant stop. it makes sense because you loose all vaccum in boost. but i was wandering is this common or not? i was thinking about making a vaccum box to have a secondary source of vaccum. any input would be great.

 

They actually make vaccum pumps that go inline with your brake booster to help with this very problem!

I have seen a few links on here under brakes faq but don't have the time to link one right now >.< sry bro

 

your brake master shouldn't see boost anyway, so the issue here is do you have anything attached to that vacuum hose? maybe you are getting boost past the check valve and in the diaphragm?

 

Check to see if you have the backflow/check valve on the vac hose to your Master Cylinder. My buddy Zach didnt have one on his RX7....needless to say his antilag launches didnt work well. You would damn near have to be World's Strongman to hold that brake pedal down at 18psi

 

what if the brake pedal does the exact opposite and when im holding the brake it slowly goes down to the floor and i have to pump it to build pressure again?

 

yeah like schister said, there is a check valve that would prevent the master cylinder from seeing positive pressure.

 

if u did use that brake booster vac line as a vacuum source make sure you tapped before the check valve (side closer to the intake manifold) and not after it...i dont see why there wouldnt be one there in the first place..

 

yes, make sure the check valve is in and functional.

if the pedal goes to the floor there is more wrong with your brakes. master cylinder may be dead. out of fluid. and/or air in the lines.