Hard Pedal - no brakes - weird ABS feel What is going on

[PkB2014]

Had a scary incident this weekend at an Autocross event. Coming into the first turn going maybe 60mph, went to hit the brakes and the pedal wouldn't go down, just hard pedal and no brakes (or very little brakes, hard to know 100%) thankfully it was a big open surface and i just kept going into cones and a big water puddle, but avoided the course workers. After coming to a stop I pumped the brakes and they seemed to start working again, i made a couple start and stops to test and seemed ok, so i exited course. It felt like something was blocking the pedal from moving so I checked the footwell when I got back to grid and found a quarter. Thought maybe it somehow got lodged in there somehow to block the pedal, IDK. We then had a couple hours break and then I and my co-driver ran 3 more runs each later in the evening. We didn't get the "hard pedal, no brakes", but I did feel ABS pushing back on me harder than normal especially at the finish where we had to shut it down pretty quickly after hitting probably 70-80mph or so. We both felt something was off still. I was running Hoosier A7s for the first time, and had 315-30/18s up front with the 345-30/19s in the rear. So the F/R ratio was not exactly OEM.

2017 GTC with TA Group
Traction Control / ESC all full OFF

Anyone else had anything like this? Did the 315s in the front cause this weird reaction? I have another Gen V Viper friend says this happened to him a couple times and caused off-track incidents and he was running standard 295-30/18 fronts. Kind of scary to think this is a normal failure. Any advice on this is appreciated. I may swap back to Kumhos and run another event to confirm the tires are not the issue, but IDK, brakes are kind of important. I want to say I had another weird brakes issue a few months back when i first ran the Kumhos, but i brushed it off thinking I did something wrong, and I never had any issue since. But now looking back maybe it was the start of this issue.

[Lawineer]

I've experienced similar in my C7. "Ice mode" is what it was called. Basically, if it's going fast and suddenly locks up, it freaks out and thinks you're on something very slick and severely limits braking power to prevent lockup. It absolutely sucks.

I noticed it happened in one spot on the track that was right were a bumpy hard braking zone started.

[PkB2014]

I've experienced similar in my C7. "Ice mode" is what it was called. Basically, if it's going fast and suddenly locks up, it freaks out and thinks you're on something very slick and severely limits braking power to prevent lockup. It absolutely sucks.

I noticed it happened in one spot on the track that was right were a bumpy hard braking zone started.

interesting, there was a bump right before this braking zone started, so going 60mph over a bump and into the brakes hard. But it locked out the brakes, so it never had enough braking power to lock up the tires at all. I've heard of some Camaros doing this, but never heard of our Vipers having this issue.

[Lawineer]

I couldn't tell you. That bump was fixed as a heckle from the track owner the third time I went off and didn't learn from it :lol:

[Voice of Reason]

I’ve had this happen a few times also at auto x events. It’s the worst feeling ever hitting the brakes and it being solid as a brick and not doing a single thing. Someone wondered if maybe I was hitting the gas along with the brake and the car was fighting itself but that wasn’t the feeling at all. I learned to quickly lift, press the clutch in, and try pressing again and again on the brake until it stops knowing that the run is over and all I’m trying to do at that point is not run into something completely avoidable in any car with working brakes.

[usmcfieldmp]

Interesting. If this was a repeatable issue, I wonder if it could be tested / "solved" during a track event by doing something simple like pulling the ABS fuse (I'm assuming this has one). I've done that on other cars before that had terrible ABS systems and would kick on too soon.

[PkB2014]

Interesting. If this was a repeatable issue, I wonder if it could be tested / "solved" during a track event by doing something simple like pulling the ABS fuse (I'm assuming this has one). I've done that on other cars before that had terrible ABS systems and would kick on too soon.

I'd hate for this to be the "fix". ABS works great and is better than humans in most cases.

[GTS Dean]

It could be the sudden unloading of the suspension after the bump or ripples under hard braking that is causing some dynamics that are difficult for the ABS to resolve. I would think that the late model 4-channel system ought to be able to handle this easily, even if the tire diameters are mismatched to a modest degree. The ABS and stability systems have a good bit of dynamics overlap that takes computing power to sort and that might be an issue here if not for having the switches off.

[PkB2014]

Gees, so the fix is to hope it doesn't happen again. ha. I never had this happen in 5 years of ownership and 3 years of autocross. But I've gotten much faster recently with the stickier tires so maybe i'm coming in hotter to the turns now. I would've thought maybe Cable would have seen this and had a fix if anyone had since he seems to do the most and the fastest racing. IDK, I guess I will shoot Morgan at ViperExchange a message to see if maybe it could be the brake booster. I'd rather have a hardware fix and it never happen again than be wondering if today is the day I have no brakes. Thanks for the input guys, I'll let you know if I find out anything else.

[Arizona Vipers]

This has never happened to me and I have ran the same exact size you are, as well as every other tire/sizes available for the track.
The only thing that ever happened to me was on Pirelli slicks which were a little taller in the front (ratio vs stock vs the rear height) and the car just went into limp mode for awhile on track, then it snapped out of it and car ran fine the whole weekend. Almost like it had to learn it was on the track, then was ok with it. The same thing happened to Pappy, I think with your same exact tire size A7's. But not what you describe above. But never heard of this except (what was said above) in Vettes, they call it "icing" and it's common once running an ultra sticky tire like A7's. The Viper ABS is a race ready system by Bosch developed on the track, the Vette is a consumer ABS. I'm wondering if you have a bad wire somewhere. Calvo had recent issues at COTA with his abs and they found a bad wire near the wheel.

[PkB2014]

This has never happened to me and I have ran the same exact size you are, as well as every other tire/sizes available for the track.
The only thing that ever happened to me was on Pirelli slicks which were a little taller in the front (ratio vs stock vs the rear height) and the car just went into limp mode for awhile on track, then it snapped out of it and car ran fine the whole weekend. Almost like it had to learn it was on the track, then was ok with it. The same thing happened to Pappy, I think with your same exact tire size A7's. But not what you describe above. But never heard of this except (what was said above) in Vettes, they call it "icing" and it's common once running an ultra sticky tire like A7's. The Viper ABS is a race ready system by Bosch developed on the track, the Vette is a consumer ABS. I'm wondering if you have a bad wire somewhere. Calvo had recent issues at COTA with his abs and they found a bad wire near the wheel.

Thanks for the input. I'll look into it more and try to get with Morgan on it. Maybe I'll shoot Calvo a DM once he's back from his trip, too.

[txA&M08]

Just want to add my $.02 here. This has happened to me a couple times, and my co-driver in the last event we ran. Seemed to happen at the end of a long straight. A quick transition from gas to brake and the brake would be as hard as a cinder block, with zero brake torque. Come off the brake and go back in and then it's there, but by that time it was too late. On 2 occasions we each had ourselves an offroad excursion due to this issue.

ViperExchange guessed it might be a brake booster issue. Maybe the check valve needs to be replaced? I was going to try this as a precautionary measure before the next track day and see if it helps.

[PkB2014]

I'm gonna switch to the Kumhos for a two-day event this weekend here in Houston. If I can't reproduce then I'll assume it was something with the oversized Hoosiers on the front.

[LATAMUD]

Just want to add my $.02 here. This has happened to me a couple times, and my co-driver in the last event we ran. Seemed to happen at the end of a long straight. A quick transition from gas to brake and the brake would be as hard as a cinder block, with zero brake torque. Come off the brake and go back in and then it's there, but by that time it was too late. On 2 occasions we each had ourselves an offroad excursion due to this issue.

ViperExchange guessed it might be a brake booster issue. Maybe the check valve needs to be replaced? I was going to try this as a precautionary measure before the next track day and see if it helps.

This is the closest answer to what I was going to add. Years ago in my 03, had same loss of brakes issue end of an autoX session. Paxton supercharger is what we assessed, boost and high rpms into multiple quick braking and we think we just momentarily lost all the vacuum to the booster.
I added a remote vacuum canister tucked in the damaged wheel well in front of the gen3 gills. Never had that issue ever again.

[PkB2014]

This is the closest answer to what I was going to add. Years ago in my 03, had same loss of brakes issue end of an autoX session. Paxton supercharger is what we assessed, boost and high rpms into multiple quick braking and we think we just momentarily lost all the vacuum to the booster.
I added a remote vacuum canister tucked in the damaged wheel well in front of the gen3 gills. Never had that issue ever again.

Yeah, that's a possibility. I ran 2 events this weekend with the Kumhos and didn't have any issues. So, I'm leaning toward the car didn't like the 315s. I'll keep an eye on it. But in the meantime i'll have 2 tires slightly used for sale soon.