01/12/2023
>My Infiniti's back brakes are new, I used the best parts and took all the precautions to keep them clean going together, but they squeal in reverse especially in the morning. What did I do wrong?
Nine times out of ten the noise from the back disc pads is vibration of the entire pad inside the confines of the knuckle. The rear pads are significantly smaller than the front pads so they are prone to resonant vibration that is perceived as a loud squeal at very low speeds and very light pedal pressure. The most likely cause for this is EXCESSIVE CLEARANCE between the pad in the knuckle guides, either from wear or careless cleaning that removed metal from the knuckle and left a large enough gap between the knuckle support structure and the brake pad. Even having the shims in place and properly installed does not affect the likelihood of the noise, because the tolerance between the shim and pad is close when the assembly is manufactured - and as miles accumulate and brake jobs are performed, this clearance gets big. The shims are there only to eliminate rattles, and cannot contain high frequency vibration of the pads, which is essentially what you hear every morning. The fix is to make all surfaces in contact with the pad flat and capable of distributing the load of the pad against it. Plus, the clearance needs to be *minimized*, not merely big enough to allow new pads to be hung - that may be too much clearance. This is a critical added precaution in a brake job, because a standard brake job involves removing rust and debris but not actual material from the knuckle. Rust is ultimately the cause of all the conditions that make the squeal happen, because removing the rust puts the clearance beyond the manufacturer's spec for quiet operation.