Brakes Pulsating At Very Low Speeds - 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 11-27-2018, 09:03 PM
flagnorfail flagnorfail is offline
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2006 Chevy TrailBlazer LT
Dark Green/Silver Two Ton 4.2L I6 4X4
Join Date: Apr 2012
Location: Rockford, IL
Posts: 9
Brakes Pulsating At Very Low Speeds

Took my 06 LT in for service yesterday to our mechanic for what I figured to be a brake issue.

- At very low speeds usually nearly stopped the brakes will pulse and make noise. Much like ABS is being engaged. It's not always at the same speed but usually this is when it happens.
- No ABS light shows up on the dash during this.
- Peddle becomes slightly mushy during this.

Mechanic says the front rotors are warped, and they are replacing under warranty because I had them changed there not long ago. They call me say it's all set to go. My wife gets into the car and at the very first stop light it does it again and does it all the way home. I jump in and take it around the block and get it to do it a couple times, but then it goes away for a while. Snow is on the ground and at high speeds if I slam on the brakes I can feel the ABS engage but again there is no light on the dash saying so.

Any thoughts on this? ABS light comes on when the ignition is turned on and vehicle goes through it's checks but it doesn't seem to actually be working when it is being engaged during operation.

Said mechanic also replaced pads/rotors on the rear, replaced a windshield washer pump and did an oil change during this service. Pretty upset that when I got the truck back I noticed on the paperwork there was 5.5 quarts of oil used for the change (I know the truck requires 6.9) also the oil change light was not reset. This automatically tells me the mechanic was in a hurry and did not pay much attention to his work. Which is also probably why they went straight to warped rotors for the brake issue.
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  #2  
Old 11-28-2018, 12:39 AM
Akrich Akrich is offline
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2005 Chevy TrailBlazer LT EXT
Dark Gray Metallic 4.2L I6 4X4
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Location: Durango, Co.
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I can only comment that the ABS light only comes on at start up and if there is an issue with the abs. Not when it engages.
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Old 11-28-2018, 11:55 AM
EnvoyBoy2004's Avatar
EnvoyBoy2004 EnvoyBoy2004 is offline
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2004 GMC Envoy SLT
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The problem is with the front wheel speed sensors. Either one is defective, but more likely there is a build up of rust or corrosion under the mounting plate.The rust raises the sensor just enough to affect the sensor's voltage output. Have your mechanic inspect the area under the mounting plate. If he is a good mechanic, he may also have a way to measure the sensor's voltage output. That will tell him where the problem is.
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Old 11-28-2018, 12:36 PM
flagnorfail flagnorfail is offline
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2006 Chevy TrailBlazer LT
Dark Green/Silver Two Ton 4.2L I6 4X4
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Location: Rockford, IL
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Quote:
Originally Posted by EnvoyBoy2004 View Post
The problem is with the front wheel speed sensors. Either one is defective, but more likely there is a build up of rust or corrosion under the mounting plate.The rust raises the sensor just enough to affect the sensor's voltage output. Have your mechanic inspect the area under the mounting plate. If he is a good mechanic, he may also have a way to measure the sensor's voltage output. That will tell him where the problem is.
A friend of mine just text me and said the same exact thing. He said likely they need to be cleaned. I'm actually going to have him look at it in his dad's shop instead of taking it back to where I had it. It's a hassle for us to get it back to this particular place, so I'm not going to deal with it.

They also mentioned that the tech notes show 7 quarts of oil were used for the change, and that the lady up front had a typo. Oil level is fine too. So just a mistake on the paperwork for that.
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  #5  
Old 12-01-2018, 11:51 AM
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John in RI John in RI is offline
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2005 BowTie TrailBlazer LT
Olympic White '50U' 4.2L I6 4X4
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I've encountered this problem on both my Trailblazers; It's a real uncomfortable feeling when the brakes 'let go' as your coming to a complete stop !

The 2004 I owned had minor pedal 'mush' when coming to a complete stop and I was able to correct the problem by removing the ABS sensor from each hub and cleaning it and by blowing compressed air into the hub. In the case of that truck there was some grease on the tooth ring inside one of the hubs. Put it all back together and no more brake fade when stopping at red lights !

I bought a 2005 to replace the 04 after the 04 was wrecked last spring. It had the same brake fade problem at low speed - but MUCH more significant. ( almost felt like I was going to crash into the car in front of me when stopping at a light. ) I removed the sensors and used compressed air again, but after reinstalling everything the problem persisted. I took both sides apart again and replaced both ABS harnesses with used parts and this time made sure to clean\scrape all the rust corrosion from the HUB around the ABS sensor hole. Don't know if the rust corrosion around the hole or the original ABS sensors were bad, but the brakes don't fade - even a tiny bit - anymore.

IMO it's a good idea to get/have replacement ABS harnesses available and ready to install before taking the wheels off and cleaning everything up real good. They are cheap enough and while I'm sure that in most cases a good cleaning of the original harnesses will resolve the problem,.... you might just save more time and $$ ( if your not doing the work yourself ) to simply replace the ABS harnesses when you first get into this repair. Otherwise - you might be doing this job twice !

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