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Discussion Starter · #1 ·
My problem is when Im just about to make a complete stop my brakes get spongy and if you push them in more then you stop immediately. what will cause this. ive read about the hydroboost lines and found that one possibly is leaking. Tried bleeding and all seems ok there. Any other input would me awesome.
 

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It only does it right when you are about to stop, and not when you initially apply the brakes? If so I would say your brake lines need to be flushed. Sounds like water in the lines starts boiling and dropping pressure the longer the brakes are applied. Or it could be a rubber line is starting to give out on you.
 

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Discussion Starter · #3 ·
yea only when almost to a complete stop and the pedal gets real soft and either pump the brakes or press the pedal and it tightens back up. its been doing it about a year and was waiting to change the pads and rotors before really digging into and its about that time now. ive looked for bulging lines and have found nothing and how would water get in the lines? maybe a good flush is all it needs idk.
 

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First thing I would try is to disable the ABS. Not sure how to do it on something that new but on older stuff there was a big fuse in the underhood fuse box. Removing it would put on the brake and ABS light but did disable the system. You want to try this first because its possible that there is a sensor issue that is making the abs system think there is one or more wheels locked so its engaging the system to try and help you stop. With the fuse out it cant do anything so you are left with a purely mechanical system. If it never does it with the fuse out then you need to get a scan tool on it to see which wheel its staying is locking up and that will be the one with the bad sensor. New sensor (which could be a hub assembly) will likely fix it. WHen the pedal drops you get that vibration like the ABS normally does but the pedal does not kick back at you.

The symptom with the hydro boost is like you describe where its all fine till you get to the point where you need to apply extra pressure to make the complete stop and at that point the pedal just drops. A split second after it drops the boost kicks back in and the brakes respond like you just slammed the pedal to the floor which causes you to lift off which of course does not make the car stop so you push down again and the whole process repeats. I guess what causes this is wear in the 'sweet spot' in the booster. IN this spot that it spends a lot of time at some fluid bypasses the piston so you basically loose the boost but as soon as you move it further it seals again and you suddenly get boost. Another symptom of this is when the boost kicks back in the pedal kicks back pretty hard. It really kicks, its not a slight vibration like the abs its a good solid thud. I was told that once they get that bad its like any other piston like thing where machining is required to fix the problem so its not a typical DIY repair, you end up getting a new or rebuilt unit.

A worn MC or just generally messed up brake system won't usually give symptoms as specific as the booster or ABS.
 

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I'm mobile or I'd link it for you.....search "achilles heel" or "sliding on ice" under heymccall.
You have a front WSS (Wheel Speed Sensor) physically out of range. Corrosion on the outside of the front hub mount or a worn out hub bearing... it's one or the other. It is NOT a fluid or hydroboost issue. It is the ABS reacting to false information. It Should set a damned ABS fault code, but it doesn't..it does lengthen stopping distances and I refer to it as the "Achilles heel" of the system.
 

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Yep, its the speed sensor. Had the same problem on my 2000 and my brother's 2004. You are rolling to a stop and at about 5mph it feels like the brakes drop out. That's because the abs kicked on and abs is meant to operate when you are pushing the pedal hard. Gives the impression that the brakes are lost.


If you pull the abs fuse the abs light will come on and the problem will be gone. Then as suggested, you'll need to figure out which sensor it is. Try just cleaning up the sensors first before buying new ones. Sometimes you just need to remove a little corrosion.

Good luck.
 

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Discussion Starter · #7 · (Edited)
wow thanks thats a ton of good info. and once in a while when turning into a parking place and stopping at the same time the abs light will kick on then go out once i come to a complete stop. im gonna replacw the pads rotors and that leaking power steering line regardless and do a hydroboost flush its never been done so wouldnt hurt and ill look at the sensors as well and try the pulling the.abs fuse.
 

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and once in a while when turning into a parking place and stopping at the same time the abs light will kick on then go out once i come to a complete stop.
This exact thing was happening to my truck. I knew my front bearings were bad, so I had them replaced. If I remember right, new front hubs come with a new ABS speed sensor (if I'm wrong on that, I'm sure someone will correct me shortly). Regardless, after replacing the front wheel bearings, the problem disappeared. To check the bearings, jack up the front of the truck, grab the top of the wheel and try to move it in and out. There should not be any play.
 

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If I remember right, new front hubs come with a new ABS speed sensor (if I'm wrong on that, I'm sure someone will correct me shortly).
You are correct, they come with a new sensor.

 

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Had this issue in my 06 silverado 2500HD code said left front WSS so we replaced it. Bearings were fine no play. Now ABS light is on all the time wont go out but if you hook up to the computer the code is in history not active. What do I need to do to get it off?
 

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Discussion Starter · #11 · (Edited)
Well got new rotors pads and abs sensors on the front. Also got the new hyrdoboost line on and flushed. Now that ive got all of that done everything seems better but now instead of like the brakes getting spongy at about 5 or 10 mph while making a complete stop now the abs kicks on. what other sensors are there? I took abs fuse out and the truck stops normal how it is supposed to. I also checked the bearing for play everything seemed snug and no play either. While I was crawling around under there today I also looked at the rear rotors and looks like they are gonna need replaced as well so thats the next thing to do but wat else could cause the abs to engage when there is obviously no loss of traction or anything like that.
 

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