Brakes unresponsive in accident

[scuba]

So I hit a guardrail with the passenger side of the '22 Powerboost FX4 (In 2H), and after first contact, the brakes failed to respond, resulting in the truck proceeding to drive through an additional 20-30 feet or so of guardrail (and 3-4 cedar posts) beyond what I felt like it could have stopped within. The initial impact ripped the front passenger wheel clean off, so that was certainly part of it, but my question for you guys: Is the braking system of the truck vulnerable to failing to deliver braking power in a situation like this?

I'm not an expert, but have gotten used to losing some braking control with ABS over the years, and knowing these are even more complex brakes, with the regen and other traction control systems, thought I would ask. If there are scenarios when braking could be unpredictable, I'd like to know and familiarize myself with them.

thx in advance for any knowledge...

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[oncechance]

Glad you did not get hurt but why did you play with the guardrail?

 

[imnuts]

Without a picture, hard to say, but if the front wheel was ripped off, it likely also damaged the brake line. If that happened, most vehicles have all the brakes tied together for fluid supply under normal situations, so the system probably lost a bunch of fluid and had no way to build pressure to activate the brakes on the other 3 wheels. Your only option at that point would have been the parking/emergency brake which is mechanical.

 

[scuba]

Glad you did not get hurt but why did you play with the guardrail?

Thx-- grateful no injuries. Wasn't on my phone, the road just narrowed suddenly w/ zero shoulder to cross a creek (country road). But there's not a good excuse. Obviously mad at myself, and will suffer (I expect months) of missing the truck.

 

[scuba]

Without a picture, hard to say, but if the front wheel was ripped off, it likely also damaged the brake line. If that happened, most vehicles have all the brakes tied together for fluid supply under normal situations, so the system probably lost a bunch of fluid and had no way to build pressure to activate the brakes on the other 3 wheels. Your only option at that point would have been the parking/emergency brake which is mechanical.

This is very helpful. I did see brake fluid squirting out, and that makes sense they'd all be connected. I'll try the parking brake next time. Are you sure it's mechanical? I only ask b/c when I was later in the wrecked truck, it said something about brake failure and (I thought I remembered) "service parking brake".

 

[scuba]

pics.

 

[Oxford_Powerboost]

Sorry to hear that, glad you’re alright though! But yeah, given that the front wheel was ripped off, I bet the system was unable to build much if any brake pressure. Hard to think of in the moment, but pulling and holding the park brake button will apply the park brake which is mechanical and doesn’t need brake fluid

 

[Chili]

I know in older vehicles the front and rear brakes ran through a distribution block of sorts that meant if you had total hydraulic failure up front you would still have something out back and vice versa. Is this not the case anymore?

 

[imnuts]

I know in older vehicles the front and rear brakes ran through a distribution block of sorts that meant if you had total hydraulic failure up front you would still have something out back and vice versa. Is this not the case anymore?

That is possible. They are at least partially isolated by the ABS pump/solenoids. Even still, the rear brakes are small in comparison to the stopping power of the front. Hard to say how much additional help they would have been given the pictures.

 

[Tomatoboy]

I know in older vehicles the front and rear brakes ran through a distribution block of sorts that meant if you had total hydraulic failure up front you would still have something out back and vice versa. Is this not the case anymore?

My recollection is that 4-channel ABS there’s a valve for each individual wheel for actuation but not leak sealing, so you’d be limited to a (mandated) split circuit between front and rear at the master cylinder, and so a leak in one wheel can still depressurize the whole axle. Regardless, a loss of 25%+ of breaking force just from the loss of one front wheel will be noticeable, as you’re losing not only one of your most effective brakes but the traction of that front wheel, and losing a whole front axle would be VERY noticeable Since you’ve lost *well over* half your braking force, considering how much more work the front brakes do.

(If you’ve ever tried to stop a vehicle after a front brake circuit failure with just the rears, or with just the parking brake you know rears don’t do a ton of work. My personal most tushie-clenching was a Ford Taurus that lost front brakes. It had drums on the rear, so when they went I took a lengthy ride towards a passing train, groaning to a stop just barely in time.)

 

[Tomatoboy]

Sorry to hear that, glad you’re alright though! But yeah, given that the front wheel was ripped off, I bet the system was unable to build much if any brake pressure. Hard to think of in the moment, but pulling and holding the park brake button will apply the park brake which is mechanical and doesn’t need brake fluid

I don’t know if the console models have their electronic parking brake control in the same spot, but the control on my bench seat truck is actually in a spot I’d have to lean significantly forward to reach in an accident. It’s one of the very few dumb control positioning decisions I think Ford made with this generation.

 

[JEB]

I know in older vehicles the front and rear brakes ran through a distribution block of sorts that meant if you had total hydraulic failure up front you would still have something out back and vice versa. Is this not the case anymore?

That’s the way I though it worked, too. The master cylinder is supposed to be divided into two chambers so if you lost hydraulics on one axle, you still had some braking power from the other axle. I was driving a 2017 Transit dually and the brake line on the right rear broke loose and I lost all brake control on the rear brakes. I still had some braking power from the front brakes but stopping distance was greatly extended.

 

[tbinmd]

Master cylinders are typically split and sometimes the brake fluid resoivour has a wall that prevents a leak from draining both circuits.

The other thing you have going for you in this situation is the speed, and you were most likely no longer on pavement. Depending on the surface you were on, you can be hard on the brakes and it will not feel like the vehicle is slowing down due to the ABS kicking in.

I had an off at the track once and when my car hit the grass I was sailing my way down a hill into a tire wall. Never felt the car slow down. ABS can be evil, in some situations and in those type of situations you are better off locking the brakes, and flat stopping the tires. But ABS will not allow to do that.

 

[Bryan Simon]

Front and rear brakes are separated by federal mandate beginning with model year 1967.
That being stated, if you lost a front wheel, you most likely lost your front braking entirely.
The rear brakes dont do much more than keep you going in a straight line under hard braking.
Front brakes are way over 70% of your stopping abilities, particularly if you have an empty bed.

Losing rear brakes is noticeable, but you still have quite a bit of your abilities left assuming there is nothing in the back. A loaded pickup or van--different story.

If lost rear brakes more than a couple of times in my 79 Chev pulling a trailer.
Kinda hair raising, but at least I was slowing down. Trailer did not help a lot, but it did help.

Started checking those wheel cylinders quite often for leaks after a couple of those episodes

 

[JoeValentine]

80% of a trucks stopping power comes from the two front tires. Losing one means you lose about 40% of your braking ability. Also, vehicles do strange things in crashes. Loss of contact with the road, overlap with guardrail, and any excess speed can make for a very surprising and stressful experience.
Bandit is the best by the way

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