Crazy theory with my brakes

[ZionXIX]

So the other day I drove to a friend's house. They up a rather tall mountainous area with basically a 20 degree incline for like a mile. When leaving their house it was all down hill so I only had to hold the brake pedal down and cruise down the slope. At one point the brake kept moving down and I lost brake pressure. I had to pull the E-brake and pull to the side hoping to hit some brush or something but then a couple of pumps later the pressure was back. I didn't have a problem the rest of the way down. To start, my pedal feels like weak sauce to begin with. I have a theory that maybe 1 other more of the brakes piston was stuck and my constant pressure going down may have "unstuck" that piston instantly dropping the pressure. Since I already have to floor my brake to get pressure there was no more travel room for the pedal to pump more fluid. So a couple of full pumps restored fluid to fill in the pressure vacuum created by the now moving piston. Am I crazy?

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[tvpierce]

You overheated your brakes and boiled your fluid.

What you did is exactly opposite of what you should have done in that situation. When faced with a long downhill run like that, you want to let the tranny control your speed so that you rarely have to use the brakes. Try it next time you visit your friend.

Your lucky you didn't end up in the ditch... or worse.

Oh, and yeah... you're crazy!

 

[pluton]

Agree with TVPierce: Compression braking was called for on a long, steep hill. Old saying of truck drivers: Never go down hill in a higher gear than it took to go up the hill.

 

[mtbtim]

You overheated your brakes and boiled your fluid.

What you did is exactly opposite of what you should have done in that situation. When faced with a long downhill run like that, you want to let the tranny control your speed so that you rarely have to use the brakes. Try it next time you visit your friend.

Your lucky you didn't end up in the ditch... or worse.

Oh, and yeah... you're crazy!

I agree with this wholeheartedly. You need to learn to use "Engine Braking". Many people who own vehicles with automatic transmissions don't know they can shift their transmission like a manual and use lower gears to slow them down. Your first downshift is taking off overdrive. The next downshift is shifting down to 2nd. If you are on a particularly steep hill and want to creep down it, you can even use 1st.

You wouldn't want to switch off overdrive until your going 65 mph or less. If I'm remembering correctly, you could downshift into 2nd when you hit around 40-45 mph. For 1st gear, you need to be going pretty slow, 20 mph or less. You just don't want to be over-revving your engine. Pay attention to your tachometer when using this technique.

Once you learn this, you will probably never overheat your brakes again unless you happen to be towing a heavy load down a steep grade and the descent is very very long.

 

[Sean K.]

I agree with this wholeheartedly. You need to learn to use "Engine Braking". Many people who own vehicles with automatic transmissions don't know they can shift their transmission like a manual and use lower gears to slow them down. Your first downshift is taking off overdrive. The next downshift is shifting down to 2nd. If you are on a particularly steep hill and want to creep down it, you can even use 1st.

You wouldn't want to switch off overdrive until your going 65 mph or less. If I'm remembering correctly, you could downshift into 2nd when you hit around 40-45 mph. For 1st gear, you need to be going pretty slow, 20 mph or less. You just don't want to be over-revving your engine. Pay attention to your tachometer when using this technique.

Once you learn this, you will probably never overheat your brakes again unless you happen to be towing a heavy load down a steep grade and the descent is very very long.

I agree with everyone else on engine braking......you don't want to use the brakes in the mountains if you can avoid it...that's one reason why I prefer manual transmissions.

Regardless, it *could* also be that your brake master cylinder is about to shit the bed. I had similar warning signs before mine went, though I wasn't in the mountains at the time. Just something to be on the lookout for.

 

[St Runner]

Since ZionXIX drives on roads like that every day I am sure he knows what he is doing. I would say the master cylinder is going and your brake fluid needs a total change. If you pump the brakes when they start to go to the floor and you get pressure back its your master cylinder.

 

[animator]

Technical term for that is called brake fade. Like mentioned, the brakes get hot and the fluid boils in the lines causing a loss in pressure.

Downshift into a lower gear and let the engine slow you down. I do it all the time in the winter if the roads are slick...

 

[ZionXIX]

Since ZionXIX drives on roads like that every day I am sure he knows what he is doing. I would say the master cylinder is going and your brake fluid needs a total change. If you pump the brakes when they start to go to the floor and you get pressure back its your master cylinder.

Thanks for the vote of confidence St Runner bit I have zero experience driving in the mountains. I've never heard of down shifting going down hill. I'm glad I asked about it. I wasn't even braking for a minute when it happened. Had it in drive the whole time. Scared the shit out of us. I was aware that I "could" downshift an automatic while driving, it just never occurred to me that I "should". I need to change out the fluid anyway. Maybe bleeding will fix my weak pedal feel.

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[Tyler James Inc]

I think there needs to be more training when we all start driving. It's kind of just a "here- figure it out!" sort of deal. If we aren't taught by someone with well rounded experience driving in all conditions, it's no different than giving someone a pistol to carry for protection, and not teaching them proper handling and shooting skills and safety practices.

Just to emphasize what others have already said-
When descending any kind of decent downgrade- especially for over 1/4mile plus(dependent on speed and load), you don't want to ride your brakes. They WILL overheat and fade(fail).
Don't be afraid to use your brakes, just make sure you modulate usage; don't ride them.

 

[Sean K.]

Thanks for the vote of confidence St Runner bit I have zero experience driving in the mountains. I've never heard of down shifting going down hill. I'm glad I asked about it. I wasn't even braking for a minute when it happened. Had it in drive the whole time. Scared the shit out of us. I was aware that I "could" downshift an automatic while driving, it just never occurred to me that I "should". I need to change out the fluid anyway. Maybe bleeding will fix my weak pedal feel.

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If it happened after one minute of braking....it's your MC. Fix it now....don't wait until it goes out at a more critical juncture.

 

[Tyler James Inc]

If it happened after one minute of braking....it's your MC. Fix it now....don't wait until it goes out at a more critical juncture.

You think so? I feel like a minute is plenty of time to overheat the brakes- given the right(wrong) circumstances.
Maybe I'm wrong though.

 

[shahsmerdis]

does this mean he needs fresh fluid, or a master?

 

[St Runner]

If ZionXIX uses 2nd and low when he goes down the bigger steeper hills in the future and the problem never occurs again it was brake fade. If it is the master cylinder it will happen again no matter how careful he is. Time will tell

 

[ZionXIX]

So if I live to tell the tale, it was brake fade. If I die and never post again, it was the master cylinder. Decisions decisions......

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[Sean K.]

You think so? I feel like a minute is plenty of time to overheat the brakes- given the right(wrong) circumstances.
Maybe I'm wrong though.

Well, he's from an island in the Caribbean. I have no idea how steep any of the grades are that he was experiencing, nor do we know the speed at which he was traveling or how the vehicle was loaded. In the right circumstances, yes, brake fade could definitely happen in 1 minute....but without a lot more information....the safe bet is to at least check the fluid (a bad MC will often leave the fluid dark brown or black from the break down of the rubber seals) and note pedal feel as it will be another indicator of the MC's condition. In short, if you're not losing fluid anywhere and your pedal doesn't feel normal....you may have a bad MC and for the cost of replacement, I personally don't think it's worth the risk.

 

[shahsmerdis]

So if I live to tell the tale, it was brake fade. If I die and never post again, it was the master cylinder. Decisions decisions......

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you potentially have faulty brakes, and you risk other peoples lives?

 

[Toyotayoda]

I too would vote brake fade on this one. You may not have been on the brake for that long, but when have you had the hydraulic system serviced? Brake fluid is Hygroscopic, and over time it's boil resistance can be greatly diminished. If it were a master cylinder this condition would exist at all times(even when stopped at a sign or traffic light, pedal would sink, car starts rolling.) Of coarse depending on the condition of the fluid you may discover that flushing the system with new fluid causes the master cylinder to fail. Also if you have leaky axle seals, that would render your rear brakes completely useless and accelerate the feeling of brake fade, and your brakes would feel like complete doo-doo.

 

[ZionXIX]

I too would vote brake fade on this one. You may not have been on the brake for that long, but when have you had the hydraulic system serviced? Brake fluid is Hygroscopic, and over time it's boil resistance can be greatly diminished. If it were a master cylinder this condition would exist at all times(even when stopped at a sign or traffic light, pedal would sink, car starts rolling.) Of coarse depending on the condition of the fluid you may discover that flushing the system with new fluid causes the master cylinder to fail. Also if you have leaky axle seals, that would render your rear brakes completely useless and accelerate the feeling of brake fade, and your brakes would feel like complete doo-doo.

I know the fluid was changed out before I purchased it so maybe it's 2 years old. When I test drove and felt the soft pedal I immediately blamed the master cylinder since the guy said he had the fluid changed out. I bought a cheap Duralast master cylinder as a backup if the OEM one ever failed suddenly. The down hill experience was the only time I have ever felt brake fade.

I'm pretty sure I have no rear brakes. When I changed one of my axel seals I could not get any brake fluid out of the rear lines. I also have no ABS since the right front sensor wire has been severed.

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[St Runner]

Thankfully your ABS is broken, that helps. I would replace the master cylinder and replace the fluid again, but this time keep working to get fluid through the rear cylinders. It could be that the master cylinder is bad or that you have an airlock which you can't bleed out. Having your rear brakes working properly will take some of the load off your front brakes and help stop brake fade

 

[ZionXIX]

Thankfully your ABS is broken, that helps. I would replace the master cylinder and replace the fluid again, but this time keep working to get fluid through the rear cylinders. It could be that the master cylinder is bad or that you have an airlock which you can't bleed out. Having your rear brakes working properly will take some of the load off your front brakes and help stop brake fade

Why is the broken ABS a good thing? I would like to replace the sensor in the future. We lots of gravel roads where ABS would come in handy.

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