ABS issues?

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Nov 21, 2014 | 05:45 AM

madmaxxed

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Starting Member

Joined: Sep 2011

Posts: 101

From: New Hampshire

ABS issues?

I've done rear brakes, replaced one of the calipers, and had to replace a blown brake line a several months back. Since then I've had an issue which at first thought it might be just a brake bleed issue but now I'm concerned it could be more. Brake pedal feels okay but just before I get to a complete stop the pedal will press in a bit soft like and make a strange sound, not a grinding sound, but similar. My abs light doesn't come on. Could it be a simple brake bleed issue for the fronts? Confused? This is a 1999 blazer. Thanks in advance!

Nov 21, 2014 | 05:14 PM

Captain Hook

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Joined: Mar 2009

Posts: 8,453

From: Belleville, Michigan

Classic symptoms that this TSB, (Technical Service Bulletin) addresses:
http://ww2.justanswer.com/uploads/GM...s_bulletin.pdf

Nov 21, 2014 | 05:59 PM

seriosbrad

Beginning Member

Joined: Apr 2009

Posts: 45

From: Canada

I have the same "grinding" noise, I'm curious as to how a small air gap between the sensor and hub causes it to make that awful noise. Is it just over-working the ABS pump/motor somehow? I have one spare wheel sensor from working on another Blazer, maybe I'll put it on my Blazer with the noise.

Nov 21, 2014 | 07:52 PM

Captain Hook

Moderator

Joined: Mar 2009

Posts: 8,453

From: Belleville, Michigan

The air gap between the wheel speed sensor tip and the tone ring is critical for correct ABS operation. If the gap is too large, you end up with low speed activation of the ABS pump. If the gap is too close, the sensor contacts the tone ring and destroys the sensor, immediately. The air gap is adjusted by using shims, (if/as necessary) between the sensor and the hub. This is done during the manufacturing process of the hub assembly. For this reason, it is not recommended to replace just the sensor. The problem is that the wheel bearing/hub assembly starts to rust under the speed sensor. The rust causes the sensor to raise up, which increases the gap between the sensor tip and the tone ring inside the hub. If you remove the sensor and clean the rust off of the hub, it takes care of the problem.

Nov 22, 2014 | 09:35 AM

madmaxxed

Thread Starter

Starting Member

Joined: Sep 2011

Posts: 101

From: New Hampshire

I did replace the driver side wheel bearing/hub assembly last year. I will take a look at the passenger side and see if the rust/crud build up is causing the issue with the speed sensor. Thanks for the info!

Last edited by madmaxxed; Nov 22, 2014 at 01:52 PM.