No brake immediately after psi boost. Not check valve or booster
Thread Starter
Launching!
Joined: Feb 2017
Posts: 225
Likes: 19
No brake immediately after psi boost. Not check valve or booster Need some help. It’s downright scary to be in third gear, near full throttle, the car pulling like a freight train — then you stab the brake pedal and it’s hard as a rock. Thankfully, the second press is totally normal.
I replaced the check valve. The old one held vacuum just as well as the new one. Even added a second inline valve.
Vacuum line from the back of the manifold to the booster isn’t leaking.
Did a leak‑down with a vacuum gun: pulled 15 inHg, and after 20 minutes it dropped to 7. Could be the three different hose sizes I Frankensteined together, but all the connections felt tight.
When I start the car with my foot on the brake, the pedal softens quickly. When I shut the car off with pressure on the pedal, I don’t feel it push back. After releasing and reapplying, I still get vacuum assist — but noticeably less on the second press, and by the third it’s basically manual brakes.
Boost gauge shows 14 inHg at idle and low 20s off‑idle.
A brake booster isn’t a “while you’re in there” job, so I don’t want to replace it unless it’s absolutely the culprit.
Next step is adding a vacuum reservoir and/or a vacuum pump.
Thoughts? And if a new booster, reservoir, or vacuum pump is the move, I’m looking for top‑tier, safety‑grade parts only.
Thank you.
I replaced the check valve. The old one held vacuum just as well as the new one. Even added a second inline valve.
Vacuum line from the back of the manifold to the booster isn’t leaking.
Did a leak‑down with a vacuum gun: pulled 15 inHg, and after 20 minutes it dropped to 7. Could be the three different hose sizes I Frankensteined together, but all the connections felt tight.
When I start the car with my foot on the brake, the pedal softens quickly. When I shut the car off with pressure on the pedal, I don’t feel it push back. After releasing and reapplying, I still get vacuum assist — but noticeably less on the second press, and by the third it’s basically manual brakes.
Boost gauge shows 14 inHg at idle and low 20s off‑idle.
A brake booster isn’t a “while you’re in there” job, so I don’t want to replace it unless it’s absolutely the culprit.
Next step is adding a vacuum reservoir and/or a vacuum pump.
Thoughts? And if a new booster, reservoir, or vacuum pump is the move, I’m looking for top‑tier, safety‑grade parts only.
Thank you.
So, I don't think you have a booster or check valve issue, I've had two boosted 4th gen Camaro's both with power brakes up around 14-15 lbs. and never had an issue. Now I also don't hit the brakes right after lifting from a WOT pull, I wait a second until the chassis settles and then hit the brakes. Are you hitting the brakes immediately after WOT because you may need to wait for the pressure in the intake to revert back to vacuum. Is your BOV working correctly, perhaps its not opening and bleeding off boost pressure quickly enough. Now @LS1Formulation replaced his booster after having some odd hard pedal issues but I don't think his issues were happening after WOT but perhaps he can chime in. If all these things check out, I'd look at getting an electric vacuum pump off a new GM car/truck like below.
GM Auxiliary Vacuum Brake Booster Fits Camaro STS HHR CTS OEM 20804130 | eBay
GM Auxiliary Vacuum Brake Booster Fits Camaro STS HHR CTS OEM 20804130 | eBay
Thread Starter
Launching!
Joined: Feb 2017
Posts: 225
Likes: 19
Thanks for the reply. Yes — the issue happens when I brake immediately after boost (9–14 psi). If I wait a second or two, the pedal returns to normal. I’ve had a couple moments where I couldn’t wait, and the second press stopped the car ‘normally’.
The BOVs seem to work at low boost. Under heavy load the engine/exhaust are too loud to hear them, but I can try the other springs that came with the BOVs(?). For context, I’m pretty sure these BOVs that came with the turbo kit lare knockoffs — I already had to replace the turbo kit wastegates with Turbosmarts.
I’m fine adding a vacuum pump if that’s the fix. Sounds like good insurance regardless.
What I don’t get is why the booster loses vacuum so fast — even with two check valves — after only a few seconds of boost. I thought these booster give 2-3 good brake pumps after shutting off the motor (?)
The BOVs seem to work at low boost. Under heavy load the engine/exhaust are too loud to hear them, but I can try the other springs that came with the BOVs(?). For context, I’m pretty sure these BOVs that came with the turbo kit lare knockoffs — I already had to replace the turbo kit wastegates with Turbosmarts.
I’m fine adding a vacuum pump if that’s the fix. Sounds like good insurance regardless.
What I don’t get is why the booster loses vacuum so fast — even with two check valves — after only a few seconds of boost. I thought these booster give 2-3 good brake pumps after shutting off the motor (?)
Thanks for the reply. Yes — the issue happens when I brake immediately after boost (9–14 psi). If I wait a second or two, the pedal returns to normal. I’ve had a couple moments where I couldn’t wait, and the second press stopped the car ‘normally’.
The BOVs seem to work at low boost. Under heavy load the engine/exhaust are too loud to hear them, but I can try the other springs that came with the BOVs(?). For context, I’m pretty sure these BOVs that came with the turbo kit lare knockoffs — I already had to replace the turbo kit wastegates with Turbosmarts.
I’m fine adding a vacuum pump if that’s the fix. Sounds like good insurance regardless.
What I don’t get is why the booster loses vacuum so fast — even with two check valves — after only a few seconds of boost. I thought these booster give 2-3 good brake pumps after shutting off the motor (?)
The BOVs seem to work at low boost. Under heavy load the engine/exhaust are too loud to hear them, but I can try the other springs that came with the BOVs(?). For context, I’m pretty sure these BOVs that came with the turbo kit lare knockoffs — I already had to replace the turbo kit wastegates with Turbosmarts.
I’m fine adding a vacuum pump if that’s the fix. Sounds like good insurance regardless.
What I don’t get is why the booster loses vacuum so fast — even with two check valves — after only a few seconds of boost. I thought these booster give 2-3 good brake pumps after shutting off the motor (?)
Joined: Apr 2006
Posts: 3,911
Likes: 1,158
From: Grand Rapids, Michigan
Mine didn't have a hard pedal immediately after boost, but the booster was definitely bad. Hard pedal sometimes, other times it would stick on after applying the brakes. Replacement wasn't terrible, and now my brakes work perfectly again. I would be replacing it if I were you, whether with a hydroboost or electric boost as others have suggested.
Thread Starter
Launching!
Joined: Feb 2017
Posts: 225
Likes: 19
Mine didn't have a hard pedal immediately after boost, but the booster was definitely bad. Hard pedal sometimes, other times it would stick on after applying the brakes. Replacement wasn't terrible, and now my brakes work perfectly again. I would be replacing it if I were you, whether with a hydroboost or electric boost as others have suggested.
