Recently my 04.5 has developed a "humm" sound which is a lot like a drum brake partially sticking/vibrating. It makes the sound after the truck has been driven for a while (everything is warmed up or hot), and it only makes the sound at very low speeds (2-3 mph).

It happens after I release the brakes, say at a stoplight, and begin to slowly accelerate, or when i'm coasting down to a stop (near 5 mph).

Anyone had this issue? I was thinking it could be a sticking brake caliper or a bad u-joint.

One more thing - how are the emergency brakes configured on these trucks. Do they apply pressure to the rear pads via hydraulics or is there a drum brake bore milled into the rear rotor center section and drum brake shoes for the emergency brake? - never had my rear rotors off.

Thanks
Eric

 

... one more thing... doesn't do it all the time, its intermittent, i.e. hard to diagnose.

Eric

 

The park brake is an internal drum setup in the rear disk....try going in reverse once the noise starts or slightly apply the e-brake and see if the noise goes away