Total brake failure on my 2018 SI Coupe. Looking for any info on how this could have happened, or anyone with similar experience.

[Wjmyazi]

I'm glad you are ok. I just can't believe you went UNDER the guardrail!



No, even though they share the same fluid reservoir, a failure in your clutch shouldn't compromise your brake system.

It seems you had two completely independent failures at the same time: electronic (CC wouldn't cancel in any way) and hydraulic (in both separate circuits!). What are the odds?



By going limp, do you mean your brake pedal went all the way to the floor with no resistance?

BTW, our cars have an emergency brake function that applies the parking brake in case of failure of the conventional brake system. No need to pull the ebrake in an emergency. I wonder why it didn't activate though...

Yeah, no resistance. I thought if there was air in the lines pumping would bring it back but it was gone. Are you talking about the auto collision mitigation braking by any chance? If so, my SI is a 2018, and that was before they came with HondaSense and the emergency braking system.

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[VTecYoSelfB4UWreckYoSelf]

Hydraulics is what I suspected. I didn't realize the brake and clutch shared the same MC. I recently had my clutch replaced at a shop. Could that have been the cause at all?

Someone told me that when you pull the ebrake at high speeds it pumps the brake?

Replacing the clutch recently is the only red flag I'm seeing. If the braking system isn't opened or disturbed it usually doesn't spontaneously fail.

 

[Guitar_stitch]

Hydraulics is what I suspected. I didn't realize the brake and clutch shared the same MC. I recently had my clutch replaced at a shop. Could that have been the cause at all?

It's not the same MC, but the same fluid reservoir. The reservoir sits above both master cylinders, so I wouldn't expect a complete failure of one system to immediately disable the other. However, I could fathom a scenario where there was gradual fluid loss that went unnoticed until catastrophic system failure.

Thinking about this more, the fact that the cruise system didn't immediately cancel when you hit the brakes makes me lean more heavily toward some sort of linkage failure under the dash. Normally the cruise cancel switch is tied in with the pedal arm directly, but that doesn't preclude some sort of fuckery from an ill trained or careless mechanic.

I would examine under the dash really carefully if you are afforded the luxury.

It's worth noting that pushing the clutch in our cars doesn't cancel cruise like in traditional systems. It will release the throttle plate, but it doesn't deactivate the system and will resume operation when the clutch is released.

 

[tacocat]

Chances of a total braking failure in this type of car with all the backup systems, highly highly highly unlikely.

Chance of things happening so fast you accidently jammed on the gas and brake in a panic, most likely.

You said it all happened so fast you couldn't remember a lot and you didn't press the clutch or take it out of gear. It's easy to catch the gas in a panic situation and not even realize it. If the car was going to have a braking system failure by now from previous work it would have happened in normal driving. The chances it suddenly decided to happen the split second you had an emergency? Like a million to one. I can't tell you the last time i've seen a true full braking failure on any Honda or Acura because they just don't happen.

 

[Wjmyazi]

Chances of a total braking failure in this type of car with all the backup systems, highly highly highly unlikely.

Chance of things happening so fast you accidently jammed on the gas and brake in a panic, most likely.

You said it all happened so fast you couldn't remember a lot and you didn't press the clutch or take it out of gear. It's easy to catch the gas in a panic situation and not even realize it. If the car was going to have a braking system failure by now from previous work it would have happened in normal driving. The chances it suddenly decided to happen the split second you had an emergency? Like a million to one. I can't tell you the last time i've seen a true full braking failure on any Honda or Acura because they just don't happen.

The only reason I'm doubting I missed the pedal, is because I didn't panic until after I realized the pedal was limp. I had everything positioned normally, and when I realized something felt wrong I even moved my foot off the brake pedal, touched my gas, and verified it was, indeed, the brake that was gone. Once that happened it's kind of a blur after that moment, but I have been *very* quick and responsive with my brakes anytime it was necessary. I just can't imagine how an hour into a road trip, I just suddenly forgot where the pedal was, y'know?

 

[Wjmyazi]

It's not the same MC, but the same fluid reservoir. The reservoir sits above both master cylinders, so I wouldn't expect a complete failure of one system to immediately disable the other. However, I could fathom a scenario where there was gradual fluid loss that went unnoticed until catastrophic system failure.

Thinking about this more, the fact that the cruise system didn't immediately cancel when you hit the brakes makes me lean more heavily toward some sort of linkage failure under the dash. Normally the cruise cancel switch is tied in with the pedal arm directly, but that doesn't preclude some sort of fuckery from an ill trained or careless mechanic.

I would examine under the dash really carefully if you are afforded the luxury.

It's worth noting that pushing the clutch in our cars doesn't cancel cruise like in traditional systems. It will release the throttle plate, but it doesn't deactivate the system and will resume operation when the clutch is released.

I'm gonna have to see if insurance can arrange something like an autopsy on the car. Unfortunately I can't see it anymore but I really want to get to the bottom of this. Not knowing is driving me insane

 

[JT Si]

I would never yank the e brake at high speed. You can use it to stop if needed in a brake failure situation which is why it's called an "emergency" brake, since it uses a different brake system than the pedal. Apparently the electronic parking brake does not function as an emergency brake from what I am reading, so just another way it's sort of useless.

That's not true. If the vehicle is moving and the handle is pulled and held for 4 seconds, the TCS will apply maximum brake force to all 4 wheels up until ABS throttles the brake pressure (similar to if you just hulk stomped the brake pedal) to stop the vehicle as quickly as possible in case of emergency.

Problem is, this is the same system that controls the brakes during normal driving via controlling the hydraulic system. If there was a hydraulic issue at the brake master cylinder point, this may have helped stop the vehicle. But if the leak was lower in the system, at or beyond the TCS brake distribution block (like a line leak or a loose bleeder) it may have helped, or maybe not. Depends on if here was still enough pressure in the rest of the lines to apply brakes on the other, non leaking wheels.

 

[BABY NSX]

Man, just glad you are ok! Those pics are bad! Glad the guardrail didn’t go through the windshield!

Yeah weird that the cruise control didn’t shut off. When accidents happen it’s hard to react especially if you don’t have much time to react. Glad you are ok! Yeah really curious about the brakes.

 

[keller]

Yeah, no resistance. I thought if there was air in the lines pumping would bring it back but it was gone. Are you talking about the auto collision mitigation braking by any chance? If so, my SI is a 2018, and that was before they came with HondaSense and the emergency braking system.

Even with air in the line, you should have felt _some_ resistance in your pedal. Last time this happened to me on the track, my pedal was on the floor and the brake pressure display was showing 7psi (out of 14psi), so I was braking at half force. I don't believe it to be air in the line.

I was not talking about HondaSensing, no. See this part from the maintenance manual:

This, coupled with the Brake assist control from the VSA, should have automatically triggered the ebrake once you stomped your pedal and it detected a partial hydraulic failure.

That's not true. If the vehicle is moving and the handle is pulled and held for 4 seconds, the TCS will apply maximum brake force to all 4 wheels up until ABS throttles the brake pressure (similar to if you just hulk stomped the brake pedal) to stop the vehicle as quickly as possible in case of emergency.

Problem is, this is the same system that controls the brakes during normal driving via controlling the hydraulic system. If there was a hydraulic issue at the brake master cylinder point, this may have helped stop the vehicle. But if the leak was lower in the system, at or beyond the TCS brake distribution block (like a line leak or a loose bleeder) it may have helped, or maybe not. Depends on if here was still enough pressure in the rest of the lines to apply brakes on the other, non leaking wheels.

Indeed. Our cars have separate circuits for front and rear brakes. So we need leaks or loose bleeders in both circuits to have a complete failure.

IMO the most probable cause is some kind of linkage failure to the master cylinder.

 

[xcivicx]

Looking as the fotos you are lucky to be alive. Hitting the rail like that kills lots o peeps so much they changed thr design in ca.
But for me this has happened, coming up on a slow truck I needed to brake but nothing there. Was in cruise and lost where my foot was and hit the clutch by mistake. Lucky I had time to figure it out in time.

 

[bbeem]

The clutch and brake reservoir fluid came to my mind also. I have spec clutch and wilwood CMC. The CMC would slowly leak untill my clutch/brake fluid in the res became so low my clutch pedal would go dead. I topped off the brake fluid to the top of the res and the clutch pedal hasn't gone dead again. I always wonder if this can effect the braking system also. Didn't experience a dead brake pedal from it though, only clutch.

 

[Wjmyazi]

Just wanted to give a general update. I tried to find a way to get the car looked at to figure out what failed, but insurance is telling me my only option is to keep the vehicle as salvage, and then take it to a shop to get it inspected, but I just don't have the money or resources to tow it around and manage it. I'm bummed that I couldn't get to the bottom of it, but thank you to everyone who contributed and gave their input. I really appreciate it.

 

[bbeem]

Good luck on your future endeavors and glad you are safe. Were you able to unlock your ktuner? Or did you at least grab the ktuner unit? If you provide proof the attached vehicle was totaled out I'm sure ktuner could assist you in unlocking the unit, even if a fee might be required.

 

[Wjmyazi]

Good luck on your future endeavors and glad you are safe. Were you able to unlock your ktuner? Or did you at least grab the ktuner unit? If you provide proof the attached vehicle was totaled out I'm sure ktuner could assist you in unlocking the unit, even if a fee might be required.

I did grab the Ktuner but was unable to unlock it, they cut my battery cables as soon as they could to keep other airbags from going off.

 

[PN_man]

It's not the same MC, but the same fluid reservoir. The reservoir sits above both master cylinders, so I wouldn't expect a complete failure of one system to immediately disable the other. However, I could fathom a scenario where there was gradual fluid loss that went unnoticed until catastrophic system failure.

Thinking about this more, the fact that the cruise system didn't immediately cancel when you hit the brakes makes me lean more heavily toward some sort of linkage failure under the dash. Normally the cruise cancel switch is tied in with the pedal arm directly, but that doesn't preclude some sort of fuckery from an ill trained or careless mechanic.

I would examine under the dash really carefully if you are afforded the luxury.

It's worth noting that pushing the clutch in our cars doesn't cancel cruise like in traditional systems. It will release the throttle plate, but it doesn't deactivate the system and will resume operation when the clutch is released.

The clutch in will cancel the cruise control if you keep it in for 10 or 15 seconds.

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