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04 Silverado, potential air in ABS module



2 years ago, I performed a GMT900 brake upgrade on my 2004 Silverado with 4 wheel discs. I've always had an odd "squishy" pedal feel ever since then. It was sorta firm but it never went back to what it was before. I assumed it was because the rotors I used were cheapos. However, a few weeks ago I checked the brakes by putting the brake pedal to the floor and pushing on the gas, the truck moved forward without hesitation. I tried this again on a gravel surface and it did the same thing. Previously I could get one or both of the rear tires to spin. This is a bit unnerving since I've driven 20k miles like this and not once has the ABS kicked on...


Either way, I believe the process to upgrade my brakes was the culprit towards weak brakes and squishy pedal feel. I began by replacing the rubber flex lines because of some deep cracking, with OEM replacements. However, I think in this process I may have let some air into the ABS module. Secondly, (because car makers are great with interchangeable parts), I ended up installing one caliper upside down, so the bleeding screw was down and proceeded to attempt to gravity bleed that caliper. I think the combination of changing the flex lines and putting a caliper on incorrectly initially, then attempting to gravity bleed it caused some air to get into the ABS module under the driver side seat on the frame rail.


I believe my next step is to bring it to a shop to use a scanner (TECH II?) to cycle the ABS module to remove any air in the valves inside the module? If that is the case, does anyone know how many hours a dealer will charge? or should I ask a shop to specifically perform this?


One thing to note, I will not perform the "backwoods" method of cycling the ABS module, by finding a road with loose surface and slamming on the brakes.


Thanks for any advice!

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Some of the better Snap On scanners can cycle the ABS modules. So if you know someone that has one it would probably be a little cheaper than a dealer. Remember all it does is move the air some where else. So you will still have to bleed the air out of the system.

Edited by Duelin
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I'm in the process of replacing all of my brake lines on my 03 Silverado...I had the same concerns as you have since I pushed all of the fluid out of the rear line as blew.....

I was told this by another member in my thread : "Be sure you bleed the abs module too! If you don't, next time it gets used it will put air into the system. To bleed it, you will have to bleed the whole system then cycle the abs then bleed it again. To cycle the abs just find a low traction area without other cars or objects and mash on the brakes. Or have a gm tech 2 scan tool that can do it."

Hope this might help !



Edited by SG Lou
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