06YarisRS
07-11-2020, 06:42 PM
I recently changed my front rotors. Although I didn't do a brake bleed/flush then - I did this fairly recently - I started experiencing soggy brakes. The pedal would almost go to the floor. The car stopped fine, but the pedal was way too spongy. I started poking around and discovered that one of the old pieces of hose I spliced into the brake booster line - to tap into for my boost gauge and blow off valve - had a huge crack in it. While removing that small section of hose, I decided to check the brake booster check valve on the manifold. You could both blow into the manifold and suck air from the manifold. Strange indeed. I expected to be able to blow air into the manifold, but not suck air out. So, either it's not actually the check valve or it's broken. I dug a 3/8" a barbed aluminum check valve that I bought as an extra for my water/methanol injection system out of my junk box. I plumbed that in between the boost/BOV tee and the brake booster. Instantly, my firm pedal returned. As an added bonus, I boosted over 9 psi as opposed to my normal 7.5 - 8 psi. I may have to loosen my wastegate. Getting into sketchy territory at 9 psi with the stock engine.
All this to say, that if you have a spongy brake pedal, check the brake booster check valve. It is unlikely to be a regular failure item on most cars, but in my case, where I'm boosted, the pressure, as opposed to normal vacuum may have killed the check valve.
All this to say, that if you have a spongy brake pedal, check the brake booster check valve. It is unlikely to be a regular failure item on most cars, but in my case, where I'm boosted, the pressure, as opposed to normal vacuum may have killed the check valve.