Hello everyone, I have a 96 C1500 that makes a whistling/squealing noise starting at 20mph, and I can't really tell if it does it at highway speeds. It sounds like it's coming from the front suspension area but I'm not 100%. It doesn't seem to make the sound when turning or braking, and I know it's not a serpentine belt. I first noticed it after bleeding the brakes, and it has an ABS light which also only came on after bleeding brakes. Could these be related? Any help is appreciated
I just had a shop do the front brake pads (along with all ball joints and a lift). Would this rule out pad wear indicators? Also, I would think that this shop or the alignment shop would have noticed a bad wheel bearing, at least if it was worn enough to let the wheel have play.
Hello slow_c1500,
Here in the rust belt symptoms like yours often show up after only the brake pads have been replaced. You see, as
the original pads were wearing down, there was rust building up in the bores
behind the brake caliper pucks.
(Brake fluid is
hygroscopic -- it readily absorbs water. This is part of the reason why we are supposed to
bleed the brakes as a part of a regular preventive maintenance schedule, for not only does this absorbed
water lowers the boiling point of the brake fluid, but at the same time pure brake fluid doesn't cause the piston
bores to rust. But all of us in the rust belt who don't periodically bleed their brakes with fresh fluid can attest to
the fact that rusty bores eventually cause sticky caliper pucks.)
So once the pucks are forced back into the bore (in order to make space for the thick new pads) ...the pucks
don't have the necessary degree of freedom to be be sucked back approx. the thickness of a sheet of paper
when our foot comes off the brake pedal. So instead of the brake pads coming completely off of the spinning
rotor, they instead are just grazing the rotor, and this can cause them to break into an audible squeal.
This diagnosis is especially true IF the squeal goes away when the brakes are applied. Also, given the slight
lateral clearances that the wheel bearings run, this squeal can also be damped when you turn the wheel and the rotor
moves slightly in the direction of the squealing pad.
Given my purchase practices and driving habits, I always have to renew the brakes when I buy a well used
vehicle. But after doing so I never wear through a set of pads
before the caliper bores rust up and cause
this very sound of 'non pad retracting properly failure'.
****
Note that the above is the highest probability if the only thing changed was the pads themselves. And it's
assumed that the caliper slides were properly lubed when the pads were changed. (
GM caliper slide lube)
But if your shop replaced the calipers and the pads, and you are experiencing these symptoms, then the
shop needs to figure out why the disc brake pads aren't being fully pulled off of the spinning friction surfaces.
The bottom line is that some folks who work the brakes hard and change their brake fluid on a regular PM
schedule may be able to replace old pads with new ones and it still works. But for me, the pads last so long
that rust wins the race. YMMV.
Hope this is helpful. Once you get this sorted out, please come back and let us know what worked for you.
Safe travels --
