Brake Booster Check Valve, Loss of Power Brakes

[lmcgrew79]

I know a few people on track at very high speeds have complained about the feeling of losing power brakes , myself being one. Maybe its a lost of vacuum, abs system, or maybe this check valve. I did the service manual vacuum leak test on the brake booster and everything checked out fine, no loss of vacuum tested 2 different ways. So i ordered a new check valve and vacuum hose just to make sure. The new check valve is grey and alot more robust looking then the black one that was on my car.
Mine is a 2008, a few photos of engine bays from 2010 look to have a grey one instead. Anyone care to check to see what they have. May not solve the problem, but ill report back once tested.

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[ViperGeorge]

I would say there are a few things that can cause the feeling of brake loss. These include boiled fluid resulting in air in the lines (use high temp fluid to solve), pedal will feel spongy with air in the lines and it will happen on every corner. Over cooked brake pads that are putting more heat into the rotors than the rotores can quickly disipate resulting in brake fad (can use a fluid recirculator, cooling ducts, new pads, different rotors), will happen more when on the brakes hard. Pad kick back generally resulting from worn bearings (replace them), when the pads kick back because of rotor or hub flex the brake system must first reposition the pads against the rotor (feeling is the pedal goes down on first application then gets firm again, a slight pump of the brakes before the next turn can elminate this until the real problem is found, happens after hard cornering and shows up in next braking zone. Lastly a vacuum leak while on a long straight under full throttle (where the engine produces no vacuum) can cause the brakes to act like there is no power brakes (typically resolves quickly once throttle is lifted because engine creates vacuum again).

 

[bluesrt]

my 10 acr-x has the same black one as my 09 coupe street car. other than the x car has the ****** capped off(no small vacume line going to it) i presume do to emmisions? delete on the x

 

[lmcgrew79]

I would say there are a few things that can cause the feeling of brake loss. These include boiled fluid resulting in air in the lines (use high temp fluid to solve), pedal will feel spongy with air in the lines and it will happen on every corner. Over cooked brake pads that are putting more heat into the rotors than the rotores can quickly disipate resulting in brake fad (can use a fluid recirculator, cooling ducts, new pads, different rotors), will happen more when on the brakes hard. Pad kick back generally resulting from worn bearings (replace them), when the pads kick back because of rotor or hub flex the brake system must first reposition the pads against the rotor (feeling is the pedal goes down on first application then gets firm again, a slight pump of the brakes before the next turn can elminate this until the real problem is found, happens after hard cornering and shows up in next braking zone. Lastly a vacuum leak while on a long straight under full throttle (where the engine produces no vacuum) can cause the brakes to act like there is no power brakes (typically resolves quickly once throttle is lifted because engine creates vacuum again).

Not a feeling of brake loss, soft pedal, or air, its actually losing power breaks, so the pedal gets extremly hard. Brakes are still there just takes a second to go from hard pedal to normal pedal. It is definatly losing vacuum i would imagine, but the i check the vacuum on the old check valve for 1 min and it holds, could have been a hot collapsed hose or who knows. Only happend a few times on VIR's super long back straight above 140, then very hard braking. I know few have reported the same problems. Just though i would start a post on it.

 

[Viperless]

Talked to Russ at Archer Racing about this problem. I think he called it brake skate or something like that. The ABS controller gets confused if you hit the brakes, release them, and hit them again. We may be doing this without realizing it. The other thing he said to check was all the ABS tone rings on the wheel hubs to make sure they're tight. I'm also going to make sure everthing is clean...tone rings and sensors.

 

[ViperGeorge]

Not a feeling of brake loss, soft pedal, or air, its actually losing power breaks, so the pedal gets extremly hard. Brakes are still there just takes a second to go from hard pedal to normal pedal. It is definatly losing vacuum i would imagine, but the i check the vacuum on the old check valve for 1 min and it holds, could have been a hot collapsed hose or who knows. Only happend a few times on VIR's super long back straight above 140, then very hard braking. I know few have reported the same problems. Just though i would start a post on it.

Pretty sure then that the vacuum is bleeding down on the long VIR back straight (or you used it all going into Oak Tree) and because the engine is at wide open throttle leaving Oak Tree there is no new vacuum being supplied. However I gotta say that when I was at Daytona on the 24 hour course my ACR brakes were fine going into turn 1 even though Daytona has a super long "straight" going into turn 1 (ok its an oval but you are flat out from the bus stop to turn 1). Now it is possible that braking and lifting through the bus stop allowed the booster to regain vacuum since on the lift the engine is generating vacuum again. I have a friend who is an SRT Viper engineer, I'll see if he has any other explanation.

 

[ViperGeorge]

Talked to Russ at Archer Racing about this problem. I think he called it brake skate or something like that. The ABS controller gets confused if you hit the brakes, release them, and hit them again. We may be doing this without realizing it. The other thing he said to check was all the ABS tone rings on the wheel hubs to make sure they're tight. I'm also going to make sure everthing is clean...tone rings and sensors.

How does this explain a hard pedal (i.e. no power brakes)?

 

[ViperGeorge]

Have spoken with an SRT engineer. Never heard of nor experienced the problem. He says booster, if working properly, should hold vacuum for hours. Curious.

 

[lmcgrew79]

May be using them up in oak tree, then just never a chance to build back up, i think mbperforance had the same thing happend there in his acr x a few times. It only happended to me a few times also, in the same exact area nowhere else. Could also be the antilocks without realizing it. My brakebooster lost 0 in hg when i tested it in a min time frame, so i know that isnt the problem. It went ahead and replaced the vacuum hose also, it lays right on the valve cover, so could be getting hot. Probably wont be able to test this again, not gonna be at vir for another month or so. Mid ohio in 2 weeks, but it hasnt happened there.

 

[ViperGeorge]

Haven't been to VIR in a long time but I don't remember having the problem on the back straight.

 

[bluesrt]

Talked to Russ at Archer Racing about this problem. I think he called it brake skate or something like that. The ABS controller gets confused if you hit the brakes, release them, and hit them again. We may be doing this without realizing it. The other thing he said to check was all the ABS tone rings on the wheel hubs to make sure they're tight. I'm also going to make sure everthing is clean...tone rings and sensors.

that completely makes no sense, also a loose ring or cracked ring will definatly throw a light- hard pedal is brake booster power

 

[mjorgensen Woodhouse]

I have had this happen, but only if I "jump" on the brakes. If I squeeze the pedal things work great, learned this the hard way a couple times, and in autocross it is tough to get right with things coming up so fast. I could never find anything mechanical it was always technique for me. Not just the Viper either, I have done this in GM and Mustangs also.

 

[lmcgrew79]

Good thing is, i guess there is no harm or problem, but its a crappy feeling when it happens and wondering if your gonna have brakes in the next turn.

 

[Nadine UK GTS]

Its the ABS unit giving the hard pedal and locking you out from braking. As Mark J says if you jump on the brakes quick. You actually beat the ABS unit, only see it on track with grippy tires and a quick driver, it's refered to as ice-mode because its like the unit thinks you've locked all wheels and so locks them out, pedal goes hard... I've had it happen a few times, know Kuno Whittmer has as well, because its street car ABS not like full race ABS that can compensate.

 

[Viperless]

that completely makes no sense, also a loose ring or cracked ring will definatly throw a light- hard pedal is brake booster power

LOL...just relaying what I was told. Until there's a difinitive solution, I will look at all possibilities. However, I'm leaning towards braking technique as Mark, Nadine, and Russ have suggested.

 

[Viperless]

Happy to report that this problem did not happen during the three days of hammering on the brakes at Road America three weeks ago. Only things I did since the track day previous to that when I had the hard pedal problem was fresh brake fluid, new front pads of the same type I ran before, and I cleaned the crud off the abs sensors.