ABS causing low-speed brake pedal pulsing - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Brakes, Suspension, Wheels and Tires > Brakes

Brakes Performance Brake Upgrades

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  #1  
Old 07-23-2009, 01:51 PM
davenay67 davenay67 is offline
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ABS causing low-speed brake pedal pulsing

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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  #2  
Old 07-23-2009, 09:16 PM
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RayVoy RayVoy is offline
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That problem is usually caused by a warped rotor.

It may have been doing it with the bad wheel bearing, but you already had wobble and may not noticed.
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Old 07-24-2009, 10:40 AM
davenay67 davenay67 is offline
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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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Old 07-24-2009, 10:57 AM
GusMan GusMan is offline
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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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Old 07-24-2009, 11:18 AM
davenay67 davenay67 is offline
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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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Old 07-24-2009, 06:58 PM
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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) .
Is it possible, the ABS is right and one wheel is locking up?
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Old 07-26-2009, 11:37 AM
davenay67 davenay67 is offline
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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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Old 08-24-2009, 09:09 PM
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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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Old 08-25-2009, 05:10 PM
davenay67 davenay67 is offline
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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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Old 08-26-2009, 12:42 AM
WOOLUF1952 WOOLUF1952 is offline
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Quote:
Originally Posted by dmince View Post
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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