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Discussion Starter #1
I have a 2007 KIA Sorento and have a brake question. About 3 years ago I had the front pads changed and mentioned that the brake pedal was traveling about half way down before I felt the breaking begin so the master cylinder was changed but it didn’t really improve the pedal so I wasn’t charged for the cylinder. Since then the pedal travel had progressively gotten longer and now it travels about 2/3rds down before breaking is felt. The breaking is great but the pedal just has to go further to get it. Last week I changed all four corner pads and had all four rotors turned and bled the brakes but the pedal travel remains the same. I can pump the pedal numerous times but the pedal is the same. Any thought?
 

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Might be vacuum booster failing, or master cylinder failing with an internal leak. Good luck!
Try grabbing the brake pedal with engine running, trans in park, and pull quickly and vigorously upward on the pedal. If internal seals are losing their position this may pull them back into place....won't hurt to try. Let us know what happens.
 

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Thank you for your reply. The master cylinder was replaced about 3 years ago and at that time it didn't really change the situation and as I stated it has progressively gotten longer in its travel, but I will try your idea and as you said it won't hurt to try. The vacuum booster is the original. How would I go about checking it?
 

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I assume that when you had the master cylinder replaced, you had the system completely flushed (brake fluid)? Maybe you have air in the system. I believe that the 1.5G Sorentos (07-09) are like my 4th gen 4Runner, in that you have to have a special scan told to activate the ABS pumps to properly bleed the system...especially, the rear brakes. Or, you have to cycle the key to the ON position several times during the bleeding process. It is not just a straight bleeding procedure anymore.
 

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I assume that when you had the master cylinder replaced, you had the system completely flushed (brake fluid)? Maybe you have air in the system. I believe that the 1.5G Sorentos (07-09) are like my 4th gen 4Runner, in that you have to have a special scan told to activate the ABS pumps to properly bleed the system...especially, the rear brakes. Or, you have to cycle the key to the ON position several times during the bleeding process. It is not just a straight bleeding procedure anymore.
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Good call from Swampdodo! Newer brake systems with ABS and Traction control have added another layer of complexity to the brake system.
 

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I can't see the booster being the source of your problem. A failing booster will emit an audible "hiss" when pressed (or even when not) and the engines RPM will change noticeably. The pedal will also become hard to depress.

I would say it is the master cylinder failing, but since the problem wasn't resolved when it was changed (if they actually changed it), and it isn't losing any fluid, then I doubt it is that. A brake master cylinder that is failing will "bypass" when you have it depressed. Press down on the pedal and see if it remains in the same spot. If it stays put, you're good. If it eventually travels to the floor, the master cylinder is bad. There are no seals that can be "pulled back into place". If any of the seals moved out of position, you wouldn't be able to brake at all.

It could possibly have air in the system, but it is odd that the symptoms would keep getting worse without having an obvious leak somewhere. One would also think that pumping the pedal would yield somewhat of a change if it had air in it. Have you ever had to add fluid to the system?
 

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Thank you all very much for your input. I will have to assume as well that the system was flushed when the master cylinder was replaced. The master cylinder was definitely changed, this is a friend of mines shop that I have used for many years and he gave me the old cylinders back and didn’t charge for the new one because it was cheaper than spending time in replacing it. I followed a simple booster check procedure. Went down this morning and pumped the pedal about 4 times to remove the residue vacuum and then started the engine and the pedal went down about an inch. No leaks at any time and the only time that I have added fluid is when I bled the brakes last week. When I bled them maybe one or two very small bubbles came out. Of course, I was bleeding the system like I would on the older vehicles and it looks like that procedure will not work on this car. I think that I will let someone else with a little more expertise than myself do this unless someone here could give some specifics on the procedure.:)
 

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I've always bled the brakes on ABS vehicles the same way I have on my old cars. I know that air pockets can get trapped in the ABS unit, so I generally bleed the brakes until I have no air, drive the car for a few days and then bleed them again. I usually get a little air out the second time around and then all is good.

What I can't wrap my head around is that the problem is worsening.. Generally if there is air in the system, it'll be consistently bad - and not get any worse.

By the way - What 60 Chevy do you have? I have a few of that vintage myself.
 

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Let me back up here for a moment, this is my wife’s car and I only drive it when we are both going somewhere together, if I am just running an errand I will usually use my truck so I am not use to the feel of the pedal like I am with my truck. I ask her going back when she had the initial concern and the front pads and the master cylinder were changed had the problem gotten worse and she said that all that was done didn’t change anything. When I took the car a week or two earlier to have the tires rotated and balanced I knew that it had been a while since the pads had been changed and while the wheels were off I checked to see what the pads looked like and they were getting a little thin but not to the point that the indicator was touching the rotor. We were going on vacation soon so we took it down to have the front pads changed and that is when she told him about her concern so the brake guy at the shop drove the car to see what she was talking about. We left it and he called and explained all that he had done but that it hadn’t changed the situation but he was only going on what he knew about the pedal travel when he drove it. Back to the worsening situation, she said that it seems to have been but she just doesn’t know how to explain it. I wish I could post a video but another forum that I am on you have to use a third-party host. I am going to bleed them again this weekend and see what happens. Thank you very much for your continued help. As far as my 60 Chevy it is an Impala, 2dr hardtop sport coupe and here is a link to my build thread on ChevyTalk. You said that you had a few, any link to yours? https://chevytalk.org/fusionbb/showtopic.php?tid/308201/

I just went down and checked the pedal travel, it went down 3” the first time that it was pressed and went down 2” the second, third and so forth.
 

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Well an update on the brake pedal issue. Bled the brakes again yesterday. I started at the left rear and did the pump-bleed, pump-bleed about 5 times and nothing came out then started to move to the right rear but decided to do it a few more times because there may be air closer to the master cylinder and after about two more times I got a huge amount of bubbles came out and the strangest thing is when I closed the bleed valve more bubbles began to come out even as the bubbles from the previous bleed was traveling back toward the valve. 🤔 I would do 5 pump-bleed and then check the fluid level and then 5 more and so on and on the left side I did these 25 times before bubbles stopped coming out then I did it 5 more times. Moved to the right rear and started the pump-bleed as on the left rear and after about 8 times I began to get bubbles but no bubbles after the valve was closed as I did on the left side. Did this for 25 times because the bubbles stopped sooner. Move to the front brakes and no air bubbles came out but did each side the 25 times. Did a test drive which included picking up some more brake fluid 😁and few additional miles and I could tell a little different and later in the evening I started the check all over again. Left rear after a few bleeds I get more bubbles but none after the valve was closed this time and stopped after 10 pump-bleeds because the bubbles stopped. Right rear very few and very small bubbles this time and stopped after 10 pump-bleed. Front no bubbles this time but still did 10 pump-bleeds and the brake pedal was significantly better when I test drove it. Drove about 50 miles this morning and did the procedure over again on the rear wheels 15 times each and no bubbles at all and the brakes feel pretty good now. 😊I’m not sure what the capacity would be, excluding the master cylinder, but it seems that it took quite a bit of fluid before the air came out. Here is a link to a short video of the bubbles that I mentioned above.
I guess in effect I have just done about 4 full system flushes in two days, I used 1 ½ 32oz bottles of fluid, and now I am thinking about trying to link up with a KIA pit crew 🏎because as many times that I have jacked the car up, took off the wheels and bled the brakes, reinstall the wheel and let it down I have gotten pretty quick. Lamar
 

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I believe this is why you need the special scan tool to 'ABS' bleed the system, but glad you got it worked out. Something that might have worked...works on 4th Gen 4Runners...cycle the key to the on position several times to activate the ABS pump and then bleed the system...or have the engine running and bleed the rear brakes. By the way, it is not the ABS system we are dealing with these days...it is also the EBD (electronic brake-force distribution) system as well...kind of like a dynamic proportioning valve system.
 

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I believe this is why you need the special scan tool to 'ABS' bleed the system, but glad you got it worked out. Something that might have worked...works on 4th Gen 4Runners...cycle the key to the on position several times to activate the ABS pump and then bleed the system...or have the engine running and bleed the rear brakes. By the way, it is not the ABS system we are dealing with these days...it is also the EBD (electronic brake-force distribution) system as well...kind of like a dynamic proportioning valve system.
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