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2002 chevy trailblazer_ltz
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Discussion Starter #1
I changed the drivers side wheel hub bearing last night, the bearing was so bad that the TB made the most terrible clunking sounds when turning right..!!
This is not my car, so I hadn't realized that it had gotten so bad, and so quickly.

Anyway, prior to this replacement, the ABS light was on. After replacing the bearing, I took the car for a test drive and noticed that the new bearing made the car drive very smoothly again, and the ABS light had also gone out. Great news..!!

However, there is a new aspect to the TB where the brake pedal pulses lightly when coming to a complete stop. This happens at very low speeds. No shake is present in the steering wheel. The brakes feel great at higher speeds. The only thing seemingly not quite right is this small pulsing of the brake pedal at low speeds.

I'm thinking it has to be ABS related, as it only started happening after the ABS system came back to life.

Any ideas on what may be happening here..??

Is this a problem..??

Thanks,
Dave. :)
 

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2002 chevy trailblazer_ltz
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Discussion Starter #3
Ray,

My first thought was warepd rotor(s) also, but the pulsing is much too fast for how quickly the vehicle is travelling. You can be at a virtual standstill and the pedal is pulsing a few times a second.

Since my original post yesterday, the TB has now started making a noise in conjunction with the pulsing. I could be off a little here, but it sounds like the noise is coming from the brake pedal area. As for the noise itself, it is really hard for me to describe it. The best I can do is to say that it is like a creaking/groaning noise, not too loud and not too obnoxious.

The vehicle stops just fine, the only time the pulsing and noise appear is immediately before the TB comes to a complete stop.

Kinda weird, hoping the collective genius on this site has ideas. :)


Thanks,

Dave. :)
 

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2003 chevy trailblazer_lt_ext
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284 Posts
I had this happen to me on my former 95 Monte Carlo. It ended up being the ABS Sensor. It was thinking the wheel was locking up when it wasnt. Ended up having the sensors replaced under warranty.
 

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2002 chevy trailblazer_ltz
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Discussion Starter #5
Gus,

Your description makes total sense.

The ABS didn't work at all prior to the new hub bearing, so now the wheel bearing that was not replaced might have an ABS sensor that is causing strange readings and making the pedal pulse.

If I could get the sensor off, I might be able to try and clean it. The ABS sensor appears to be be held on by one bolt and something that looks like a big rivet. I was curious about the sensor on the dead bearing, but wasn't able to remove it. Didn't spend too much time as I was concentrating on replacing the bearing whilst the daylight was still good.

For all I know, this wheel bearing is still the original, meaning that it already has 100K under it's belt, and that it may not last too long before a replacement is needed.

Dave. :)
 

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2009 chevy
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Dave, you could prove ABS by just pulling the fuse. Without power, the pulsing should go away.

Gus has a good suggestion (the ABS thinks one wheel has locked up) :thumbsup:.
Is it possible, the ABS is right and one wheel is locking up?
 

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Discussion Starter #7
The pedal pulsing happens at about 1 mph, or even slower maybe, immediately before coming to a complete stop. I can rule out the wheel actually locking for sure.

I really think the ABS sensor in the older hub bearing is causing confusing readings. Given the age and mileage of the bearing, i really think it will die and need replacement before this year is finished. I'm betting a new hub bearing and ABS sensor will cure this little issue.

I mainly wanted to make sure it's not a sign of a bigger problem that I should be worrying about..??

Dave. :)
 

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Brake clatter at stop

Dave,

How'd you make out with this mince is doing the same thing.

The ABS system is activating just as I come to a full stop. Is there something I can check and replace or does it need to see the chevy doctor?


Also, the other day the brake were grabing sometimes when I first hit the pedal. Not all the time though. Could this be a master cylinder or an ABS problem?

Seems to only happen when they're hot. Did it more today. Is it possibly boiling the fluid. Fluid has been in for 110k miles. I haven't had the brake system open, but, could there be air in the system.

Any help would be apprieciated.

Thanks,
dmince
 

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Discussion Starter #9
Hey dmince,

I know for sure my problem is related to the ABS sensor, the problem ceases when the ABS sensor in the hub bearing is unplugged from the main harness.

Given the age of the bearing and the build up of crud, I am waiting for the iminent demise of the bearing to finally cure this issue.

If I were you, I would definitely change your fluid and bleed your brakes. You may experience good results by undertaking this maintenance, so try this and see how things work after this.

Dave. :)
 

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2003 gmc envoy_slt
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7,190 Posts
Dave,

How'd you make out with this mince is doing the same thing.

The ABS system is activating just as I come to a full stop. Is there something I can check and replace or does it need to see the chevy doctor?


Also, the other day the brake were grabing sometimes when I first hit the pedal. Not all the time though. Could this be a master cylinder or an ABS problem?

Seems to only happen when they're hot. Did it more today. Is it possibly boiling the fluid. Fluid has been in for 110k miles. I haven't had the brake system open, but, could there be air in the system.

Any help would be apprieciated.

Thanks,
dmince
You have 110k on the original brakes?!? As Ray said, pull the ABS fuse and see if the pulsing goes away.
 

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Western Canada Chapter
2003
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6,411 Posts
Hey dmince,

I know for sure my problem is related to the ABS sensor, the problem ceases when the ABS sensor in the hub bearing is unplugged from the main harness.

Given the age of the bearing and the build up of crud, I am waiting for the iminent demise of the bearing to finally cure this issue.

If I were you, I would definitely change your fluid and bleed your brakes. You may experience good results by undertaking this maintenance, so try this and see how things work after this.

Dave. :)
I wouldn't wait. I would have had this fixed yesterday. :m2:

You have 110k on the original brakes?!? As Ray said, pull the ABS fuse and see if the pulsing goes away.
:iagree:That's what I was thinking. That old fluid is probably not doing anything good to the brake system at this point.
 

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I'm also having the same ABS issue when coming to a stop on my 2003 Trailblazer. I replaced the drivers side half shaft. In the process, being new to cars with ABS, I used a C clamp to push the brakes piston can in (about 1/8") so I could get the caliper back on. After putting it all back together, my brake waring idiot light came on and the dashboard readout says service brake system. I've heard I messed up my ABS system. I bled the brakes, and that stopped the two warning lights from coming back on, but the ABS keeps rapidly pulsing the pedal when stopping once the car gets below 10 mph. I read the information above, and took out the fuse for the ABS, and the pulsing stopped (ABS and both brake warnings mentioned above came on). I pulled the drivers side ABS sensor off the hub and cleaned it and the rotor it senses. I have not cleaned the passanger side sensor yet (yes I took it out to when working on the drivers side half shaft to get the intermediate bearing assembly off). Is there an ABS valve that I messed up by pushingb the brake fluid backwards through the system? Where is it if there is? If it is the ABS sensor on the hub, how do I diagnose which one is bad? Can you jack the car up (all 4), take a sensor out and try the brakes to see if pulses? Or do I need to plug the hole, and take the car out for a test drive? Is there an easier way to diagnose what is wrong? Thanks, Mike
 

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Well, I started reading the thread and then realized that you replied to a 2 year old thread with a new issue. :nono: No offense, but that kind's kind of annoying.

I've been compressing the caliper pistons with a C clamp on ABS for years without problems. I was taught many years ago, before working on brakes with ABS, to pump the brakes 5 or 6 times until the pedal is rock hard. This is with the ignition off. I'm not sure if you did that, but it sounds like you didn't. Are you getting an ABS malfunction light?
 

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There's another recent thread with the exact same issue. Turned out to be a bad bearing hub. Possibly yours got tweaked when you removed the axle from it. I would replace that one first. If still doing it, replace the other. Could just be a coincidence.

Yeah, zombie threads. You should have started a new one :nono:
 

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2005 chevy trailblazer_lt
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ABS Problems - Wheel Bearing Hub Assy. WIth Sensor

You can buy a new hub bearing assembly WITH sensor WITH shipping costs included for $65 at 1AAuto.com. Why spend $200 worth of time trying to avoid a $65 expense?
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I don't recommend haphazard, random parts replacement, but a new assembly is necessary between approximately 150k - 185k miles anyway.
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Also, just like brakes or tires, it is best to bite the bullet and replace both front bearing assemblies at the same time.
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While an auto forum may not seem like the place to quote Shakespeare, "A coward dies a thousand deaths. The brave die once."
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Die once and be done with it.
 

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2004 chevy trailblazer_ss_ls
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brake pulsing

i have read that the sensor may have some crud buildup on it, & that cleaning
it may help. I have this issue with my 04 tb, but haven't tried clean it yet.
greck48
 

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2004 chevy trailblazer_ss_ls
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+low speed brake pedal pulsing

I have this issue on my 2004 trailblazer also, makes a funny sound just b/4
stopping. I think it started shortly after replacing the left front hub bearing.
right hub was replaced about 1 year b/4. wonder if it's a cheap replacement
that doesn't pick up correctly.
 
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