Brake system keeps blowing caliper seals

[Xrider]

My vehicle is a 2004 2500HD Duramax 4x4 with 260k miles. Over the last eight months have installed five sets of new rear brake calipers consisting of two sets of AC Delco calipers, one set of Raybestos, and one set of PowerStop, all purchased from RockAuto. Each of the first four sets failed in less than 500 miles, pushing fluid past the piston seals.Last week the local Chevrolet dealership service and parts managers recommended a set of GM OEM rear calipers. I did and in less than 150 miles, both OEM units are leaking past the seals. Prior to the 1^st installation, the system was completely flushed and new DOT4 fluid added. Have since flushed the system a 2^nd time and added DOT3 fluid. The brake light and ABS light illuminate when the ignition is activated and go out in a couple seconds, as usual. No codes show up. The brake lines all appear good. There is no noticeable change in braking behavior like lockups or pulling. Discovered some warpage this morning in the rear rotors and had them turned. I had not felt any vibration during braking and doubt this could be the problem. Thanks for any assistance.

[spongebob]

Im thinking the warped rotors..

[Xrider]

Thanks for your response. My brake system is getting air into it from somewhere. Discovered this by continuous gravity bleeding. There's no indication of leakage in the lines, around the ABS Module or pressure control switch or the master cylinder. I have new lower lines to the calipers. I now assume the air is the reason for the seal failures, and the warped rotors might also be a factor. I'm suspecting the ABS Module or pressure control switch might be the air source. I have a new master cylinder but haven't installed it yet. Any other ideas greatly appreciated.

[Xrider]

Am following up my first post above. Ignore my post on air in the system, that's not a problem. Since my first post, have done the following and have not solved the problem. Thought the problem might be caused by warped rotors so turned the rotors which did have some warpage. I then installed another new set of AC Delco calipers and within 100 miles both rear units were leaking fluid through the piston seals. Except for the brake lines, which appear in excellent condition, the only things left to replace are the ABS Control Module and the pressure differential switch below it. Your input is appreciated.

[DmaxMaverick]

Where are you seeing the leaked fluid, and how much? Is there a corresponding fluid loss at the master cylinder, and how much? The master cylinder rear-brake reservoir is small, so any loss should be obvious. The only thing I can think of that might cause a caliper failure that quickly is excessive heat, such as from a dragging E-brake. They just don't fail that easily, or that often. Be certain the fluid you are seeing is actually brake fluid. An overfilled axle or failed hub seals will cause axle lube to leak onto the rotors and caliper area. An axle flange leak (very common) generally makes a mess, but could also leak lube onto the rotor area, but that should be ridiculously obvious.

[Xrider]

Thank you - as soon as I read your post I knew! It's axle fluid. I had changed bearings, races, seals and axle fluid in 2021, so the idea it was leaking didn't come to mind. I don't drive the truck as much since I've retired. Also, the 75w90 synthetic axle lube is still mostly clear, looking more like brake fluid until you actually rub it between your fingers. Now I just need to discover why both sides starting leaking at the same time? Thanks again. I appreciate your response.

[DmaxMaverick]

If both sides began leaking at the same time, I'd suspect the axle was overfilled. AAM (the axle manufacturer) revised the fill level. It should be 3/4" BELOW the fill hole, NOT the traditional AT the fill hole level. I think the lube difference is less than a quart, so it isn't much. Their reason for the revision, as I recall, was that an overfull may cause the inner axle seals to leak.

That said, it is likely your seals aren't failed. What happens, due to an overfill, is normal thermal expansion causes the higher fluid level to obstruct the vent, and create a positive pressure condition in the axle, which forces the lube to pass the axle seals.

As well, if you're seeing a fluid leak, the E-brake shoes are likely contaminated with axle lube. If it hasn't been for long, you can simply clean the lube from the shoes, inner drum (inside the rotor, AKA: Drum-in-Hat), and area with brake cleaner. Most often, the E-brake returns to normal function. If the shoes are saturated and the lube has penetrated the friction material, they should be replaced.

[DIESEL/VETTE]

WHAT WOULD WE DO WITHOUT DmaxMavrick?