Yesterday I experienced something rather scary. I'll admit, I was aggressive and stupid. "Messed with" another vehicle, and down-shifted to third at about 65 MPH, and accelerated to the redline, then I braked hard as there were other cars on the highway. My car was not stopping very quickly, and I stood on the brakes. It felt like someone greased my rotors. It was VERY slow braking. The situation diffused, but was very unnerving. I attempted to brake hard again a few minutes later, and it felt fine. Pads and rotors appear fine. Driving to work this morning at about 50 MPH, I stood on the brakes, and it stopped immediately with slight chirping of the tires.
This is a VERY big problem if you cannot brake at high speed. Not sure what's going on.
Any ideas?

 

Just spitballin' here, but if I understand your description, you were WOT, at redline, in 3rd gear and immediately braked hard. I'm not sure it's possible but "maybe" you inadvertently found a fraction of a second when there was insufficient vacuum for the brake booster. It might help if you can clarify exactly the circumstances at the time of braking. Did you get off the throttle completely then to the brakes or was there any overlap time with WOT and braking?

I will be interested to see what the group has to say about this. Be patient for responses the next couple days.

 

Pretty rapidly switched from WOT to hard braking.
Another note is that I don't think I pumped the brakes - just stood on them. Felt like I was trying to stop a dump truck.

 

What pad are you using? You may have faded them..

 

I'm not sure. They were installed when I bought the car.
Is that an indication when you can practically lock up the wheels (as much as antilock will allow) at 50 MPH, but can't stop at 100+?
I do know rotors can get "glazed" from heat. I don't know if that's my issue, either.

 

Main causes of brake fade


Brake fade is a reduction (or total absence) of the stopping power of your brake system that occurs as a result of overheated brake pads. Simply put, it's when you push on pedal and the vehicle doesn't slow like you planned. No amount of additional foot pressure can make you stop quicker. While it is most commonly associated with race cars and heavy trucks that put high demands on the braking system, as you'll read below it can occur on any vehicle that uses friction based deceleration.

It's a particularly significant issue compared to other system failures because once the driver has hit the brakes - they've already committed to the event and there isn't much time to correct when it goes awry. Brake fade manifests itself with a very firm yet ineffective brake pedal. If your braking issue is not accompanied by a firm or hard brake pedal - you don't have brake fade. You will need to look deeper for your issue.

So how do you know if you have brake fade?
◾Your brake pedal is firm (soft pedal is a different condition)
◾Your brakes are not effective.
◾Pumping the brake pedal does not help
◾Once the system has cooled, performance usually returns (although permanently at a reduced effective level)

 

Was there ABS activation with a pulsing pedal, or was it just a hard pedal? Was there any noise when you hit the brake?

When the situation diffused itself, do you mean the brakes started working? What was different?

 

Sound like the brake booster check valve may not be working. Under several seconds of hard acceleration and intake manifold vacuum dropping, the vacuum in the booster could have been equalized to atmospheric pressure, or close enough, to affect the booster's assistance if the one-way check valve is not staying closed.

 

Thanks for the input.
"Situation diffused itself" = I didn't crash and drove sanely the rest of the way home.
Both brake fade and the check valve describe what's happening. I'm questioning the brake fade since the brakes were cool at the time I stood on them.
I remember it being just a hard pedal, with no antilock pulsing. The brake fade definition is very close to what I experienced. But the problem is when I stood on the brakes, I was on the highway for about 2 miles with very little braking prior. The brakes would have been very cool at that time.

The check-valve makes sense also. I'll look into replacing that first.

 

I'm wondering why didn't the ABS activate?

 

Because the wheels weren't locked up maybe..

 

A hard brake pedal makes me think brake booster check valve.
Roll the windows down or at least the drivers, drive at regular speeds, 35mph or so and preferably parallel to a wall.
Let off the accelerator pedal and listen for a very light whistling. If you hear it, check the brake booster check valve and specifically the grommet that surrounds it in the brake booster.

Mine had a small gap on the driver side of the grommet from the hose connecting to the back of the intake pulling on it. Its about $3.00 at O'Riley's

 

Thanks for the input. I purchased a new OEM check valve, and will install it soon.
Then maybe a test on an empty highway with nothing around.

 

1. If you don't want to get too fast you may try flooring the gas at low speed while in one of the higher gears so pedal can be held down long enough to simulate the event when brake problem occurred. This should drop intake vacuum considerably.
2. Just curious. Do you have a radical camshaft? Radical cams can reduce intake vacuum considerably. I had a hot rod several years ago with such a cam and I could get only about one brake pedal depression before the booster vacuum was used up. I installed a vacuum canister (from Jeg's) which increased my vacuum volume sufficiently to provide booster assistance for more than just the one brake pedal effort.

 

I had the same exact problem. I've tried to reproduce the problem but I can't. I'm guessing (based on the comments - Thank you to all) that's its vacuum on the brake booster from the sudden change from accel to the brakes. I've flushed my brake lines and inspected the brakes. Now I'll check the booster.

 

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