I am getting a whistling sound from my truck, It comes and goes and at various speeds but I have noticed that when I touch the brake pedal the sound goes away but does come back after I take my foot off the brake.
It does not sound like a pad/rotor noise, sounds more like a vacuum line?

Any idea what can be causing this?

thanks

Mark

 

Seems like you need new brake pads since it goes away once you brake. I had the whistling sound as well and it was because my brake pads need to be replaced.

 

I used to get a whistling sound similar to this from my brakes:

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If you have plenty of brake pad left, take them off and rough up the part that contacts the rotor with some rough grit sandpaper - lay the sand paper on a flat surface and rub the pad back and forth to break the glaze. Make sure all the anti-rattle hardware is still present, lightly lube the pad backing plate with a thin layer of anti-seize. I usually recommend against using the red/orange goopy "disc brake quiet" stuff.

 

On many good quality pads there are wear indicators that are sheet metal tabs that contact the disk surface once the pads get worn down to 3/16" or so and need replacing. That can sound kind of like whistling. So look at the thickness of all four pads and see if any are down that much.

If the pads are worn different amounts, then you should clean up the slots the pads slide in, in the calipers. Sandpaper and then Rustoleum Rust Converter paint does a pretty good job. Get new pins from the dealer if the old ones are rusty - those don't stay cleaned up very well.

If the original rubber brake line sections have never been changed, you might consider replacing them with new dealer parts. Don't forget the rear one that (I think) attaches to the LSPV.

Because our trucks (if 4wd) are so freeking heavy, you really need a top quality pad. I've found the dealer pads are good, and so are Hawk LTS. You can get the latter from tirerack for a decent price.