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Discussion Starter #1 (Edited)
hi guys, i suddenly experienced a sudden loss of brakes last night. i mean i could still get my car to slow down to a stop but i need to hit the brakes to the floor to do that now. feels like a loss of pressure to my brake pedals and not as safe and reassuring as it should.

continued until morning and decided to drop by at my mechanic to check. he checked it concluded it's fine and didn't even charge me, he offered me to take a seat at the driver's and check the brakes and yeah it SUDDENLY WENT BACK TO NORMAL for some reason. so i had no choice but just to describe what happened the night before. he said it sounded like my master cylinder is going away, and that it'd be a waste for me to bleed my brakes or change the fluids if that's the case. but concluded my car has no problem at the shop when he checked. there weren't any leaks and my brake fluid is full, other than that all his assessments were pure visual and no mechanical checks have been made.

now the brakes been working as it should. i assume there's air on my brakes that should be bled, my question is, does air just go away like that all of a sudden too? i don't want my problem to come back while driving at a certain speed. could it just be that my brake fluid if in need of replacement? i'm at 50k kms

*last night, i think it's important to note that before i felt that i have a brake problem, i was going at a decent speed then realized the road nearing ahead was bumpy so i had to brake fast. while my foot was on the brake pedal (midway down the pedal or what normally should) i felt it suddenly became "soft" all the way to the floor until i got a decent grip. i think it's normal for cars to have that sudden "dip" to the brake pedal floor, especially when braking suddenly for potholes and bumps, you guys would know that feeling. but that soft pedal never went away until the next day.
 

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at idle, when you press the brakes, does the RPM change?

If it does, then it's likely the brake booster.
 

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Discussion Starter #3
not at all, it's just that you had to push it to floor last night to get to a stop or slow down. and it's weirdly fine now for some reason.
 

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what year, engine, and transmission?

On the BK1 2.0 automatics, there is a vacuum pump to assist with braking, via the brake booster.

Maybe the pump hiccuped or the relay for it, didn't engage.
 

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Discussion Starter #5
2011 2.0T a/t

i have a hunch that the ABS engaged on my sudden brake (which makes sense because the pedals dipped to the floor). it's not uncommon for most cars to get air into the system once the ABS engaged too. hoping this is true though, a quick repair.

it was an uneven bumpy curve it always forget to slow down at. this isnt the first time my ABS engaged on that curve (judging from how my brakes dip all the time there). but this time my brakes doesnt revert to normal until the next morning..
 

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what year, engine, and transmission?

On the BK1 2.0 automatics, there is a vacuum pump to assist with braking, via the brake booster.

Maybe the pump hiccuped or the relay for it, didn't engage.
Idk if he didn't get the vacuum boost / assistance, the brakes should feel stiff and hard to press not soft. To me sounds more like one of MC seals / sections giving up and not holding pressure.

One way or another i would check if the line holds vacuum, check electrical connection to vac booster and so on. But really this sounds like a MC going bad.


@micoycoy go through service manual on brakes, you may need to change your MC or at-least get the seals out and change them. also did you really | really checked your car underneath for any spill or brake fluid marks ?
 

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2011 2.0T a/t

i have a hunch that the ABS engaged on my sudden brake (which makes sense because the pedals dipped to the floor). it's not uncommon for most cars to get air into the system once the ABS engaged too. hoping this is true though, a quick repair.

it was an uneven bumpy curve it always forget to slow down at. this isnt the first time my ABS engaged on that curve (judging from how my brakes dip all the time there). but this time my brakes doesnt revert to normal until the next morning..
The hydraulic brake system is a sealed system, there is suppose to be no air in the system.

When it happened, did you pump the brakes?

the brake booster part of it is separate from the hydraulic system. It's to assist in leverage through mechanical linkage to the master cylinder. It's to allow the driver to put in less effort to engage the brakes.

The reason it has a vacuum pump is because the engine is turbocharged. Normally the booster would get it's vacuum from the intake manifold on a NA engine. It does do this in some regards through check valves.
The reason why the manual doesn't have one is because, normally you engage the clutch before applying the brakes. The manual has more check valves to allow the booster to work.

When a master cylinder goes bad, it's not intermittent.

FYI the hose going to the booster has another check valve IN it. So if you go to replace that line, you can't just replace it with any hose.
 

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Discussion Starter #8
quick question if it's the master cyclinder, shouldn't i still be having the problem until now? i mean it improved since i drove it 3 times again after leaving the shop. i'm at the midway in order to get the stop i need. not the same hard pedal but enough to feel secure when braking. or does the problem only arise during hard braking last night?

i checked the calipers if they we locked last night, and underneath for leaks. we checked the leaks at the shop too (including the wheel well for fluid marks). the fluid level didn't change since last night too..
 

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Discussion Starter #9 (Edited)
@AKGC i did pump it at least once after the first braking and turning to the curve, it was then when i felt a softer pedal and a loss of braking power since i was cruising at a speed (like leaving a manual car on neutral) on a bumpy curve instead of slowing down..

the cylinder can be obvously seen at the engine bay, but not sure where the brake booster is located. are you also suggesting to have the booster itself checked or just the lines connected to it?

editied: nevermind my question just realized it's the larger part of the master cylinder
 

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.........When a master cylinder goes bad, it's not intermittent.

FYI the hose going to the booster has another check valve IN it. So if you go to replace that line, you can't just replace it with any hose.
I think you may have cases when its intermittent i.e. long no change of brake fluid/ moisture in the brakes and a worn seal on brink on going bad i could see it happening.

btw OP one thing that came to my mind ... how is your pad wear across the car - i mean is it even ? is there a chance you had a sized caliper / piston i.e. in the rear ?
 

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Discussion Starter #11
that's one thing i should get help to check as i'm alone dealing with this prob here, all the mechanic said is that my pads are still good..

i checked last night if they looked seized or whatever. touched the rotor which are not heated at all. i honestly don't know anything about the mechanics of a caliper or a piston but it's normal for the pads (not enganged) to be almost touching the rotors, correct? i'm curious since i don't know how it looks like when the pads are pressured on to the rotor, and when it's just rested parallel to the rotor disengaged

put my car on D with handbrake - and pads just sitting parallel with almost no gap. tried it on Neutral and Reverse too.
 

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I'd still suspect the master cylinder. Sometimes when they start to go bad, they bypass and don't build the right pressure to stop properly. I've had them do that for more than a few drives. Be OK one drive, then bypass the next.
 

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Discussion Starter #13
could it be a shot master cyclider or just air in the system? now the problem's completely gone
 
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