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Old 07-11-2020, 05:42 PM   #1
06YarisRS
 
Drives: 06 2ZR Turbo Yaris RS
Join Date: Aug 2017
Location: Fredericton, New Brunswick, Canada
Posts: 2,384
Soggy Brake Pedal

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.
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2006 Yaris 5 Door RS 2ZR-FE (2011 Corolla 1.8L) Swapped, Automatic, T-28 Turbocharged (8 psi), HSD MonoPro Coilovers, DIY W/M Injection, custom 3" cold air intake, custom 2.5" exhaust, TRD rear sway bar, Penguin Garage 13mm spacers (rear), custom Civic front lip, full repaint, Android 6.0 7" touchscreen, Rockford Fosgate speakers, tweeters, NVX underseat subwoofer
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Old 07-13-2020, 08:09 AM   #2
CrankyOldMan
2ZR swap. DO IT! Ask how!
 
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Good catch! I've always found the pedal feel to be pretty soft but never had it go almost to the floor to bite.
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Old 07-13-2020, 02:18 PM   #3
06YarisRS
 
Drives: 06 2ZR Turbo Yaris RS
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Quote:
Originally Posted by CrankyOldMan View Post
Good catch! I've always found the pedal feel to be pretty soft but never had it go almost to the floor to bite.
Thanks man. Yeah, it was a LOT softer than usual. I've been out for a few drives and it's good and solid now! I might still do a brake fluid flush. Never hurts, right.
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2006 Yaris 5 Door RS 2ZR-FE (2011 Corolla 1.8L) Swapped, Automatic, T-28 Turbocharged (8 psi), HSD MonoPro Coilovers, DIY W/M Injection, custom 3" cold air intake, custom 2.5" exhaust, TRD rear sway bar, Penguin Garage 13mm spacers (rear), custom Civic front lip, full repaint, Android 6.0 7" touchscreen, Rockford Fosgate speakers, tweeters, NVX underseat subwoofer
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Old 07-14-2020, 11:56 AM   #4
CrankyOldMan
2ZR swap. DO IT! Ask how!
 
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Drives: 09 Meteoric Metallic HB
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Speaking of brake flush, the Motive Power brake bleeder system is amazing! I bought the kit for my GM truck and also got an adapter for the Yaris--Motive doesn't seem to have one for our reservoir--from Assenmacher Tools: TOY18B. Pretty spendy if you won't be flushing the system more than once every 3 years but if you start doing track/race stuff it will be invaluable.
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