Hi. I'm new to this forum. I just purchased a 2006 Avalanche 2500 and am not familiar with the 8.1L. I also own a 2003 Avalanche 1500 and am pretty familiar with it. I purchased this from a used car dealership from out of state. The truck has 84k on it and overall seemed to be in pretty good shape. The dealership replaced all four calipers and brake pads. I noticed from start up and with the truck in park, while applying the brakes, there was a whining/mooing noise. I have not been able to identify the source of this but it sounds like it is coming from the engine compartment. The drive home was 8 hours through the mountains and no hard braking was necessary.

Yesterday I did a hard brake at around 30mph. The truck went into a significant skid and the pedal went to the floor. Braking distance increased from normal and no abs activation. In park, I can apply the brake pedal and with not too much effort, the pedal will go to the floor and the whining/mooing is quite audible. There is plenty of brake fluid. There are no warning lights or any indication that the abs system has a fault.

Any thoughts as to what this might be? At this point, I will not drive the truck until the problem is identified and resolved. Thank you in advance for any advice/help.

Joe