Okay, here is the story. A few months back, I felt like I had a spongy pedal, and from previous experiences, I knew that crappy pads would make it feel that way, so I replaced the rear rotors and the pads (Hawk Pads)on all four tires. I had to open the bleeder screws to compress the pistons, and to avoid further issues I bled the entire system. The result was a little bit better braking, but still a spongy pedal. Fast forward a little bit, I started to feel the ABS activating (no ABS light on the dash) at very low speed and very light braking, like 5mph to 0. So I had the system flushed. That resulted in again, decent brake performance, ABS stopped activating but still with the spongy pedal.

That lasted about 3 months, when I felt the ABS activate again, still no light on the dash, again under very light braking. Knowing that there shouldn't be any air in the lines, I start thinking Master Cylinder. So I take that off to bench bleed it, but with the crappy plastic fittings they give you, its impossible to stop it from sucking air in. So I reinstalled the master, now knowing that there is air in it, and went to the brake shop this morning. They had the tool to activate the ABS manually, to fully bleed the system, and after all was said and done, I still have an extremely spongy pedal and about 50% of the brakes that I should have.

The shop knows its not right, but they couldn't do anything more to fix it, other than replace the master, which they would have to order. With all that said, here is what I would like to know

1. Why would the ABS activate without the light on the dash pop on? That has me thinking a bad wheel speed sensor, but I am not sure about that.

2. The shop said there are TSBs out warning to use only factory Masters when replacing, which I am supportive of. Does anyone know who made the master and the part # that came factory on an 03 Silverado SS with dual piston rear calipers?

Sorry for the length, just wanted everyone up to speed with what has been done.

 

Well I don't have any helpful ideas about the poor brakeage, but as far as I know the ABS light will only come on if there is a problem with the ABS system. It doesn't come on just because the system was activated. At least it never does for me.

 

well thats god to hear. I really am not interested in changing the ABS unit. Its almost $1K.

 

There is a recall for the ABS coming on pre-maturely, I think it covers up to 03 models? It involves removing the sensors and cleaing their mating surfaces and any junk that may be on the magnet of the sensor. Rust and debris builds up where the sensor mounts, increasing the air gap between the sensor and reluctor wheel, causing the false ABS activation.

Since the system is bled and the pedal is still spongy, you could have a sticking or siezed slider pin, make sure that all of the calipers move freely and that none of the sliders are sticking.

 

Are there any limiting factors to the ABS recall? Also, I have felt a slight pull to the right when I hit the brakes, meaning the left front caliper isn't engaging at the same time, is that what you are talking about with the sticking slider?

 

http://www.consumeraffairs.com/recal...05/gm_abs.html

If this is what you are referring to, then I think I am out of luck. Although my truck was originally sold in the North East and I am having the same exact problem...

 

Yea, that's it....you can still do the repair yourself though, maybe someone has a link or can copy and paste the TSB that outlines it...

 

Incoming!!

 

#03-05-25-007D: Antilock Brake (ABS) Activation at Low Speeds (Clean Wheel Speed Sensor Mounting Surface) - (May 1, 2009)


Subject: Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)


Models: 2002-2006 Cadillac Escalade, Escalade EXT

2003-2006 Cadillac Escalade ESV

1999-2006 Chevrolet Silverado

2001-2006 Chevrolet Suburban, Tahoe

2002-2006 Chevrolet Avalanche

2003-2006 Chevrolet Express

2007 Chevrolet Silverado Classic

1999-2006 GMC Sierra

2001-2006 GMC Yukon, Yukon Denali, Yukon XL, Yukon Denali XL

2003-2006 GMC Savana

2007 GMC Sierra Classic

2003-2006 HUMMER H2




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This bulletin is being revised to add the 2007 Silverado/Sierra Classic models. Please discard Corporate Bulletin Number 03-05-25-007C (Section 05 -- Brakes).


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Condition
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction
Measure AC voltage and clean the wheel speed sensor mounting surfaces.

•Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual.
•Disconnect both the front wheel speed sensor connectors at the frame and harness.
•Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector.
•Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
•Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service.
•Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
•Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
•Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (in Canada, P/N 89022218).
•When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (in Canada, P/N 993037).
•Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
•Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.

 

double post