Constant brake squeal driving me INSANE!!! :-)

[Ulf]

Thanks for all your perspectives - been off the grid with a severe case of the dreaded man flu, but here are a few answers (and even a few more questions): Pads are original and only slightly worn and fitted after the sound arrived a few years back (have new ones and will try them later with anti squeal paste), brake hoses are all new and the pistons in the front callipers are resealed and moving freely. A novelty is that the pitch of the sound changes whenever I turn slightly - and even disappears for 10-15 delightful seconds after a sharp turn, could it be a worn bearing causing misalignment/friction? Another oddity that I might have failed to mention earlier, is that the sound only occurs when the car is up to running temperature regardless of whether I have used the brakes or not getting there - can engine heat potentially cause the (new and bled) brake fluid to expand to the degree that it causes the piston to move ever so slightly to create friction? Br Ulf

[Tyler S]

That shouldn’t happen. If brake fluid is expanding because of temperature then then any pressure created should find its way back to the reservoir. That is unless the brake pedal or MC is incorrectly adjusted and partially applying the brakes at all times. Which could also explain why calipers wont fully retract and allow pad/rotor contact.
A malfunctioning brake booster can also cause this. When the car is running, the bad booster can push the MC rod all on its own. Worth a look

[Tom in seattle]

I’ve had the experience in working on a couple of 356’s that the flexible brake line in the front have internally collapsed which causes pressure to remain in the brake line between the point of collapse and the front piston after you take your foot off the master brake.  I’ve also had a similar situation on a Jeep off road car.  What’s happening is that there is a residual pressure remaining on the disc which precludes it from floating off the disc.  Be sure you have replaced the old flex lines.  But I sympathize with you!

[Shvegel]

It sounds like you turn the wheel, the rotor flexes and the brake pads are pushed back which causes the noise to stop. It would be normal that there is some flex in the hub. This is all provided the wheel bearings are not showing any play. Before the problem started your wheel bearings were a little loose and this was masking the underlying problem.  The pads.  Speaking as a former line mechanic as well as a former BMW trainer.  Whenever I had a car that the brakes were squealing on I put factory pads in it and it went away.  Factories want parts that don't cause warranty problems.  They stop when they are cold. They stop when they are wet and they don't squeal.

My father in Law has a 1972 911 with non power assisted brakes.  One day he said he was moving through town after being parked and a kid on a bicycle ran in front of him.  He almost ran him over.  He said he needed higher performance brake pads and I finally convinced him he needed lower performance brake pads that didn't need to be warm to work.  I replaced the pads with factory pads.  Problem solved.