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#1 Old 08-26-2013, 09:28 PM
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Soft brake pedal

Hi everyone!
Got Elantra GT 6 month ago. Good car, but it seems I have a very common problem of Elantras - lost of brakes. Read a lot of complaints and solutions for the problem. And it seems there are many, many opinions on the issue. My car has TCS, but no ABS. It started 4 month ago. Car is fine for several weeks, but then within two days brake pedal getting from bad to worse. My mechanic already replaced master cylinder and right rear caliper. Did not help. Yesterday it was third time when I almost (very soft pedal) lost brakes. Today in Hyundai dealer service they bled the brakes and said "that they hope it will help". Their mechanic found air in both (left and right) rear brake lines. So, my question if I have a leak in, say, left line will it propagate to the right line? I am asking because I do not know the hydraulic schema of the brakes and want to collect as much info as possible. Thank you very much!
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#2 Old 08-26-2013, 09:38 PM
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It's not rocket science, and Elantra does not have any outstanding brake issues. Soft pedal means air in the lines. If they don't bleed ALL the lines in the CORRECT bleeding order, chances are they're just pushing the air around the system. Hyundai has a really bizarre bleeding order, so Joe's mechanic shop probably got it wrong, but the dealer has no excuse except they are the dealer and more worried about "customer satisfaction" than fixing problems.


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#3 Old 08-27-2013, 07:51 AM
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IF you have an AIR leak - it is more likely for the fluid to spill out that air to come in.
The lines are under a huge pressure. Air does not come in just like that. It must be sucked in. But there is no vacuum to suck it. Whenever you press brake - hundreds of PSI build up and compress/push the pads. All fluid would be spilled out though the hole where air would come in...

Whenever master brake cylinder is replaced - a full bleed must be done.
I am not quite sure what the tricky order is here as I changed fluid on mine and it all worked fine. Never had any brake issues.


The hydraulics is like that:
you press the pedal, it pushes the piston in master brake cylinder (via vacuum booster). The pressure increases and is split between two front lines and two rear lines. Done.
If ABS is there, you get extra lines through the ABS unit. I am surprised you got TC, but no ABS...
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#4 Old 08-27-2013, 08:28 AM
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Thank you for the quick replies! I definitely have TCS. One time I slipped on the wet grass and TCS light came on, plus I see the unit there. Maybe it is because of GT model.
Interesting I noticed one feature. When I had bad brakes I pressed the brake pedal with engine OFF and brakes were OK. Then I turned on engine and pedal went to the floor. Right now, after bleeding the system, I press the brake with engine off or on and it has no difference. Did it open some valve? Maybe valve to the rear part where air was in the lines?
I really understand what you are saying that it is more likely for the fluid to spill out than air to come in. Well, first two times when mechanic replaced master cylinder and caliper brakes were totally fine. I assume if I had air in the system it would compress and I would notice the soft pedal right after the replacements, but no it was OK for a while.
Again, I really appreciate your responses.
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#5 Old 08-27-2013, 12:40 PM
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so what is the pedal now?

with engine off the first time you press it is smooth, every next time you press it hardens. so it should be hard after 3rd time or so. hard, but brakes will work, just need much more force.
then, you start with brake depressed and it travels a little to the floor. then brake is soft, but will not change position if quickly pumped a few times.


I find it hard to believe it would have TC, but not ABS... but OK, I take it.



Can you lock the wheels now? Dry pavement? Gravel road? Begin with moderate force and keep depressing until wheels lock.

When you say soft - do you mean the pedal travels to the floor? Do the brakes respond? Then you depress the pedal again - is it hard?
How much fluid you have in the reservoir?
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#6 Old 08-27-2013, 01:47 PM
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Right now brakes like you are describing - with engine off it hardens, with engine on brake is soft, but will not change position if quickly pumped a few times. When I had bad brakes I depressed one time, turned on engine and pedal went to the floor.
When I say soft I mean the pedal will go to the floor completely and brakes respond. When I depress the pedal again quickly pedal is slightly, slightly harder. I always have full reservoir.
I did not try to lock the brakes, do not have time now. But since right now brakes are good I assume I can lock the wheels.
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#7 Old 08-28-2013, 12:47 PM
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Quote:
Originally Posted by hyundai_2006 View Post
But since right now brakes are good I assume I can lock the wheels.
so do that to check if they really work, because if they do not provide enough friction, you will find out when it will be too late... if you see what I am saying.

First try gravel/grass or whatnot, then pavement. If not ABS you must have both front wheels fully locked in any condition.
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#8 Old 08-28-2013, 01:14 PM
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Look closely at the rear caliper that wasn't changed out.

If its starting to seize it may not move piston enough to push out the air properly during bleeding. Look at the pad wear or carefully check rotor temperature after driving; comparing it to new caliper side. My 2 cents.
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#9 Old 08-29-2013, 10:56 AM
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Quote:
Originally Posted by santa06 View Post
Look closely at the rear caliper that wasn't changed out.

If its starting to seize it may not move piston enough to push out the air properly during bleeding.
false. piston movement is not needed during bleeding and does not take place at all. with the bleeder open, the master cylinder is the motive force (fluid flow) to push the air out of the caliper piston.

now i am not 100% familiar with the elantra of this era. don't they have drum brakes? if so you may have broken a spring in one of the drums causing a longer travel on one of the drums. i know you stated 'caliper' for a rear, i just want to be sure.

PLP is correct that leaking air in isn't quite right...higher pressure means fluid comes out. that being said, you mentioned master cylinder replaced. a new MC must be primed correctly to get air out of it BEFORE installation. sure that was done?

very very worn pads *could* cause a longer travel and slightly softer brakes...but it seems like something that simple would have been caught by now.
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#10 Old 08-29-2013, 10:13 PM
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So when you are pumping the brake pedal and building up pressure in the system, before you open the bleeder screw---the pistons aren't being forced against the rotors via the pads.

So how would hydraulic brakes ever function then.

GL models rear drum brakes; GLS and GT and most XD generation hatch models normally rear disc.

Hyundai 2006 was it a new OEM master cyclinder or a rebuild unit that mechanic installed.

Last edited by santa06; 08-29-2013 at 10:26 PM.
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