Brakes Intermittently Not Working At Slow Speeds
November 1st, 2016, 7:02 PM
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Brakes Intermittently Not Working At Slow Speeds
Please pardon my terminology on the below described situation. I am most assuredly *not* a mechanic, and am here seeking assistance with a particularly perturbing issue. I do hope that I have come to the right place, and will greatly appreciate any assistance that is provided.
I have a 2004 Chevy Classic, which I am told is "the same as" a Malibu. The car in question is the "base" model, 4 cylinder version. I recently had new brakes put on the vehicle, and ever since have been having issues with them. However, the issue seems to be intermittent, as it works just fine any time any of the multiple shops I've taken it to go to take it for a test drive. Basically, I keep randomly losing my brakes. Either they go entirely to the floor and are just gone until I pump them (at which point they always come back up), or "skip a section" of the pedal push, feeling like they're dropping to the floor, and then suddenly re-engage before going all the way down. However, this only seems to occur under very specific circumstances:
If I am traveling slow (under 40mph), AND I am "slow stopping" or attempting to slow down, AND I am on a medium or steeper downhill grade, THEN the above described situations will set in, but only some times. If I try to slam on the brakes, they work fine. If I'm traveling at highway speeds, they work fine. Meanwhile, I have found traveling through town, trying to come to a gentle stop at a stop sign and instead shooting out into perpendicular traffic sucks.
The strange part is that my brakes were working just fine prior to having them replaced with new brakes. And my old brakes-- well, they were the old, "probably needed replaced 6 months before I was able to do so" variety. Yet they performed perfectly. I've also noticed that since having them replaced, the top quarter to top half of my brake pedal is "dead". Gently pushing on it produces no stopping what so ever. It used to be where all I had to do was barely touch the brake pedal to get the car to start slowing down. Now I have to go over 2/3 the way down to get the car to even think about stopping, and that's assuming that the brakes don't cut out on me.
I have taken it to several shops, including the one that installed the brakes, and they can't get it to replicate the "cutting out" / "flooring pedal" issue. Each shop has also claimed that the top half of the pedal being dead is "normal" and "how it should be functioning." I am inclined to disagree, as every mechanic I had taken it to prior to moving (believe me, I'd love to be able to take it back to my old mechanic) never allowed it to act like that, and the one time it did after being serviced, I took it in and they immediately fixed it.
Additional things that I have noticed after getting the brakes serviced is that my seat belt seems to lock up a lot more often. Prior to having my car serviced, the seat belt would only lock up if I slammed on the brakes. Now it seems to lock up every time that I try to come to a slow stop (travelling at under 10 mph), and refuses to release until I release the brake and allow the car to roll forward over half a car length. I usually have to lean forward to check for perpendicular traffic when entering a new roadway, as I am short with long legs, and this is making it nigh impossible to do so.
We've checked the master cylinder, and everyone says that it's fine. We even had it replaced less than a year ago with a brand new (NOT remanufactured) model. They've also checked the "vacuum" (lines? Sealer? booster?) and it was "fine" as well. The brakes have been bled several times. I get no panel lights when the above braking situation occurs. There is the appropriate amount of fluid in the brake system, and no leaks -- they checked every inch of tubing(?) for the system, and it's all contained properly. One store even took my wheels off to check the ... "brake squeezy bits" that grab hold of the moving parts. It turned up no problems there either.
Potentially related information:
At the time that I had my brakes replaced, I also had new tires installed. During that process, they discovered that one of the "brake squeezy bits" on one of the back wheels was leaking and needed replaced. They replaced it accordingly. They also did a brake system flush, as I had informed them that I usually wound up blowing out one "brake squeezy bit" a year (all in different positions), and they suggested that perhaps there was something being transported about in the brake fluid that was causing that issue.
While I do live in a particularly hilly area, I live very close to my work place and all the grocery stores, and put maybe 50 miles on my car per week, if that. I also drive my car very gently, and do "slow, gentle" stops when encroaching on a stopping point. I most assuredly do NOT go roaring up to a stopping point only to stop at the last minute. There have been a few times that I've had to come from highway speeds to a full stop in a very short distance because someone walked out in front of me on the highway, and, as expected, that made a might bit of a terrible noise, but those incidents were prior to having my brakes replaced, and I've not had a similar incident since.
In the last 2 years, I've "blown out" 3 ... "coil packs" (?) and no one can tell me why.
Note that I always get the "good" parts with the lifetime warranties.
I have a 2004 Chevy Classic, which I am told is "the same as" a Malibu. The car in question is the "base" model, 4 cylinder version. I recently had new brakes put on the vehicle, and ever since have been having issues with them. However, the issue seems to be intermittent, as it works just fine any time any of the multiple shops I've taken it to go to take it for a test drive. Basically, I keep randomly losing my brakes. Either they go entirely to the floor and are just gone until I pump them (at which point they always come back up), or "skip a section" of the pedal push, feeling like they're dropping to the floor, and then suddenly re-engage before going all the way down. However, this only seems to occur under very specific circumstances:
If I am traveling slow (under 40mph), AND I am "slow stopping" or attempting to slow down, AND I am on a medium or steeper downhill grade, THEN the above described situations will set in, but only some times. If I try to slam on the brakes, they work fine. If I'm traveling at highway speeds, they work fine. Meanwhile, I have found traveling through town, trying to come to a gentle stop at a stop sign and instead shooting out into perpendicular traffic sucks.
The strange part is that my brakes were working just fine prior to having them replaced with new brakes. And my old brakes-- well, they were the old, "probably needed replaced 6 months before I was able to do so" variety. Yet they performed perfectly. I've also noticed that since having them replaced, the top quarter to top half of my brake pedal is "dead". Gently pushing on it produces no stopping what so ever. It used to be where all I had to do was barely touch the brake pedal to get the car to start slowing down. Now I have to go over 2/3 the way down to get the car to even think about stopping, and that's assuming that the brakes don't cut out on me.
I have taken it to several shops, including the one that installed the brakes, and they can't get it to replicate the "cutting out" / "flooring pedal" issue. Each shop has also claimed that the top half of the pedal being dead is "normal" and "how it should be functioning." I am inclined to disagree, as every mechanic I had taken it to prior to moving (believe me, I'd love to be able to take it back to my old mechanic) never allowed it to act like that, and the one time it did after being serviced, I took it in and they immediately fixed it.
Additional things that I have noticed after getting the brakes serviced is that my seat belt seems to lock up a lot more often. Prior to having my car serviced, the seat belt would only lock up if I slammed on the brakes. Now it seems to lock up every time that I try to come to a slow stop (travelling at under 10 mph), and refuses to release until I release the brake and allow the car to roll forward over half a car length. I usually have to lean forward to check for perpendicular traffic when entering a new roadway, as I am short with long legs, and this is making it nigh impossible to do so.
We've checked the master cylinder, and everyone says that it's fine. We even had it replaced less than a year ago with a brand new (NOT remanufactured) model. They've also checked the "vacuum" (lines? Sealer? booster?) and it was "fine" as well. The brakes have been bled several times. I get no panel lights when the above braking situation occurs. There is the appropriate amount of fluid in the brake system, and no leaks -- they checked every inch of tubing(?) for the system, and it's all contained properly. One store even took my wheels off to check the ... "brake squeezy bits" that grab hold of the moving parts. It turned up no problems there either.
Potentially related information:
At the time that I had my brakes replaced, I also had new tires installed. During that process, they discovered that one of the "brake squeezy bits" on one of the back wheels was leaking and needed replaced. They replaced it accordingly. They also did a brake system flush, as I had informed them that I usually wound up blowing out one "brake squeezy bit" a year (all in different positions), and they suggested that perhaps there was something being transported about in the brake fluid that was causing that issue.
While I do live in a particularly hilly area, I live very close to my work place and all the grocery stores, and put maybe 50 miles on my car per week, if that. I also drive my car very gently, and do "slow, gentle" stops when encroaching on a stopping point. I most assuredly do NOT go roaring up to a stopping point only to stop at the last minute. There have been a few times that I've had to come from highway speeds to a full stop in a very short distance because someone walked out in front of me on the highway, and, as expected, that made a might bit of a terrible noise, but those incidents were prior to having my brakes replaced, and I've not had a similar incident since.
In the last 2 years, I've "blown out" 3 ... "coil packs" (?) and no one can tell me why.
Note that I always get the "good" parts with the lifetime warranties.
November 1st, 2016, 7:45 PM
#2
sorry didn't read all that
the wheel speed sensor drop out at low speed, the abs thinks the signal drop out is a wheel lock up condition and activates the abs pump....the pump opens the dump valve to relieve brake pressure and the brake pedal drops to the floor.
at higher speeds the abs signal is stronger so the system works fine. its a inherent design flaw of passive wheel speed sensors....that is why all new vehicles use active wheel speed sensors.
the fix is to record which wss drops out with a scan tool. then you can inspect that sensor and wiring....replacing the bad parts or just clean the sensor mounting surface (depending if the sensor is integral or external to the hub)
go to the shop and tell them at slow speeds the abs pump is activating...a false abs event is occurring because the wss is dropping out....with that description they will know what they need to look for.
the wheel speed sensor drop out at low speed, the abs thinks the signal drop out is a wheel lock up condition and activates the abs pump....the pump opens the dump valve to relieve brake pressure and the brake pedal drops to the floor.
at higher speeds the abs signal is stronger so the system works fine. its a inherent design flaw of passive wheel speed sensors....that is why all new vehicles use active wheel speed sensors.
the fix is to record which wss drops out with a scan tool. then you can inspect that sensor and wiring....replacing the bad parts or just clean the sensor mounting surface (depending if the sensor is integral or external to the hub)
go to the shop and tell them at slow speeds the abs pump is activating...a false abs event is occurring because the wss is dropping out....with that description they will know what they need to look for.
Last edited by tech2; November 1st, 2016 at 7:47 PM.
November 7th, 2016, 9:42 AM
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Take your vehicle to a different shop this time... have them check to see if the zerks at each wheel are tight..they may be sucking air in one of the brakes.
Ive had this happen when i snapped off one on my truck and it didnt seat properly.. it did leak at the wheel, but i never looked..but the fix was rather beyond me. the mechanic had to use an "easyout" tool he said to extract the nipple to the brake cylinder on the right front of my truck.. hope this is something you can look at just incase you seem to have run out of options at this point.. also.. check the abs brake sensor rings at each wheel....for cracks or displacement too far from the abs sensor ok.
Kat
Ive had this happen when i snapped off one on my truck and it didnt seat properly.. it did leak at the wheel, but i never looked..but the fix was rather beyond me. the mechanic had to use an "easyout" tool he said to extract the nipple to the brake cylinder on the right front of my truck.. hope this is something you can look at just incase you seem to have run out of options at this point.. also.. check the abs brake sensor rings at each wheel....for cracks or displacement too far from the abs sensor ok.
Kat
