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I have an issue I'm trying to figure out. I have a ls9 and wilwood master cylinder/calipers and there is a problem with boost pressure feeding into the booster causing the master cylinder to pressurize and the brakes to lock up . Only does it user boost. Supply is coming off the factory location. The factory check valve can't stop it. The pressure over takes it. Can't understand why I have boost pressure bleeding back? I have to crack open the line to release the pressure on the brakes . Unhook the vacuum and the breaks work fine . With the vacuum hooked up it will idle all day and drive it with no boost it's fine. Only does it under boost . Has great vacuum.
The check valve is to keep vacuum in the booster not to keep pressure from entering so that if the engine should die while driving you'll have power brakes long enough to get the car stopped.
One fix is to just go with a hydroboost setup. You will always have good brakes and won't have to worry about lack of vacuum or in your case a pressurizing the booster.
Is this where you have your brake vacuum line plumbed?
Last edited by LLLosingit; 01-09-2015 at 11:31 PM.
I'm not familiar with that blower but on most the brake like would hook up on the vacuum side of the system, Not below the blower where it will see boost. One example is a 6-71 blower, The vacuum port for the brakes would be below the carbs and above the blower. This is a constant vacuum point. Below the blower would see vacuum only at idle like you are experiencing.
Strange-I have had 15-20 boosted cars and never run into this problem, and they all had power brakes
have you tried replacing the valve at the booster, cheap thing to try anyway
the only other thought is somehow a residual valve in the brake system is creating to much hyd. pressure in the brake system, locking them up
The brakes should release, if they don't the resd. valves are holding them
not sure if its possible, maybe boost is somehow, thru a hole in the booster, and getting to the back side of the booster-pulling the ck valve should release it though
I have used ck valves in the PCV system so boost wasn't blown back into the crankcase, maybe those would work-be interesting to see what you find
The check valve or non return valve does both those things.
It maintains vacuum in the booster AND prevents boost from entering it. It's the same thing.
It was late lol, This is true to a point. The valves were designed to stop low vacuum from escaping not pounds of boost from entering, I've seen the same thing when people have hooked the vacuum line under the blower where it see's boost, The booster didn't hold boost but it did make the brakes pretty much worthless.
We just use Hydro boost setups from Chevy Astro vans, Very cheap and work better than most vacuum systems.
Last edited by LLLosingit; 01-10-2015 at 09:28 AM.
Cant say I've ever needed anything other than engine vac to assist with brakes, other than a car using proper anti-lag which leave you with no vac at all a lot of the time.
Then just either use an electric or mechanical vac pump instead, or just remove the booster altogether and go solely mechanical
Cant say I've ever needed anything other than engine vac to assist with brakes, other than a car using proper anti-lag which leave you with no vac at all a lot of the time.
Then just either use an electric or mechanical vac pump instead, or just remove the booster altogether and go solely mechanical
My experience has always been with roots style blowers that start making boost off idle. I could see where a turbo or centrifugal would be different because they aren't making boost a good part of the time. The Hydro boost conversion isn't that hard really and it does work much better than vacuum style.
My experience has always been with roots style blowers that start making boost off idle. I could see where a turbo or centrifugal would be different because they aren't making boost a good part of the time. The Hydro boost conversion isn't that hard really and it does work much better than vacuum style.
When you're braking, your foot is off the throttle so there should always be vac available.
And even if the blower is making a little boost between blower and engine, doesnt always mean there will be no vac between blower and throttle.
I dont think the correct place to take booster vac from would be below the blower ? Surely it would be between blower and TB in the case of a rootes or twin screw style ?
So in that respect, the booster should never see boost as it would with a turbo or centri install.
I dont think the correct place to take booster vac from would be below the blower ? Surely it would be between blower and TB in the case of a rootes or twin screw style ?
As I said earlier
I'm not familiar with that blower but on most the brake line would hook up on the vacuum side of the system, Not below the blower where it will see boost.
01-09-2015, 09:37 PM
Issue with supercharger and brakes 
