Rick's Free Auto Repair Advice

Brakes make grinding noise

Why brakes make grinding noise?

Brakes can squeal and screech, and while it’s annoying, most drivers ignore it. But when brakes make grinding noise, drivers take it seriously. And they should because it’s the sign of serious brake problems.

There are many causes. Here are the top 4

1) Metal to metal contact. Friction material is worn out and the steel brake pad backing plate is rubbing against the rotor face.

2) Brake pads have failed due to overheating and glazing and friction material break-up. If the friction material has lost its grip with the steel backing plate causing it to crack or break off. All of these conditions result in excessive vibration when applying the brakes and that comes across as a grinding noise.

severly corroded brake rotor

What’s going on here? Simple: The brake pad friction material has broken off the steel backing plate. The only remaining friction is performing the braking. Since other areas of the brake rotor are no longer in contact with the brake pad, it has severely corroded.

3) Excessive vibration due to uneven brake pad application. The brake pads must apply and retract smoothly in their guide areas. Corrosion buildup that prevents the pad from moving or retracting freely will result in a sticking brake that applies uneven pressure against the rotor, decreasing braking power and causing that portion of the friction material to overheat.

Brakes make grinding noise when there’s metal to metal contact

In normal operation, the brake friction material is pressed against the brake rotor. But when the friction material wears off or breaks off because the adhesive has failed between the material and the steel brake pad backing plate, the backing plate itself is pressed against the rotor. That results in metal to metal contact that causes an awful grinding sound. The images below show what can happen when  a backing plate with absolutely no frictional material is pressed against the rotor.

Metal to metal contact wears off the surface of the rotor and destroys the brake pad backing plate.

The Fix for metal to metal contact

Replace brake pads and rotor with high quality parts. See this post on how to shop for high quality brake pads. Clean all contact areas and replace all brake hardware including anti-rattle clips, shims, caliper slide pins and boots. Use high temperature synthetic brake grease.

brake pad wear

Brake pad worn off completely down to backing plate causing metal to metal contact

worn brake rotor

The image above (upper left) shows a cutaway of a brake rotor. The rotor consists of two rotor plates, cooling vanes and a “hat” area. When you get metal to metal contact, the steel backing plate can grind off an entire rotor plate (upper right) or thin the plate so much that it can’t brake properly (bottom image).

worn brake pad

Friction material gone. Backing plate rubbing against rotor

Brakes make grinding noise when the brake pad has failed

brakes make grinding noise

Brake pad backing plate has rusted. “Rust jacking” (expanding rust) causes the friction material to debond from the backing plate. The friction material cracks, causing uneven friction material to rotor application which causes a grinding noise

brakes make grinding noise

Cracked friction material due to backing plate rust and debonding

brake pad failure

Friction material edge lift due to substandard backing plate steel that flexes during application causing debonding. This also causes grinding noise.

Brakes make grinding noise when the brake pads are seized

When brake pads can’t move freely in their slots, they apply unevenly causing a grinding noise due to excessive vibration.

The binding can cause only the top or bottom curved edge to contact the rotor. Or, corrosion can cause the top or bottom end, or “ears” to bind, causing brake pad taper. Either way, only a portion of the brake pad contacts the rotor, causing excessive vibrations that sounds like grinding.

brake pad backing plate

Excessive brake pad wear and decreased braking performance due to improper backing plate length which causes binding

Brake pads can also fail due to substandard steel backing plates that flex during application. This causes the edges of the pad to delaminate resulting in edge lift. This introduces another vibration point that can cause the brakes grinding sound.

The Fix for binding brake pads and delamination

All economy and some “OEM” brake pads are made with substandard steel backing plates that are painted. Eventually the paint degrades and the steel rusts, causing the friction material to debond.

Here’s what to look for in high quality backing plates and high quality shims.

seized brake pad

Pad special attention to the brake pad clip areas. Remove all rust from those areas and apply a light film of brake grease to prevent future corrosion and pad binding

Brakes make grinding noise when the caliper is seized

Floating calipers must slide easily along the caliper slide pins or they will not apply even braking pressure to the brake pads. Caliper slide pins can corrode and stick the bores, preventing the caliper from applying and releasing properly.

caliper slide pins

Replace corroded caliper guide/slide pins with new parts. Lubricate with high temp synthetic brake grease

Partial application of braking pressure can a brakes makes grinding sound condition.

The Fix for seized brake calipers

If the caliper slide pins are corroded, replace them along with the degraded rubber boots.

seized brake caliper

If the caliper slide pin bores are severely corroded or the slide pins are seized, purchase a replacement caliper bracket. That’s about half the cost of a new caliper

 

Brakes make grinding sound due to improper bedding procedure

Most newer brakes are adherent versus abrasive style which means they continually deposit a sticky film on the face of the rotor. When you apply the brakes, the friction material contacts the sticky film which converts rotary motion to heat to stop the vehicle.

New brake pads must be “bedded” to the rotor to apply an even film coating on the rotor face. Every manufacturer and every type of pad has its own bedding procedure. If done improperly, you can actually create excessive vibration that sounds like grinding because you’ve deposited too much or too little of a film layer.

The Fix for improper bedding

Using 150-grit sandpaper and a random orbital sander, sand the rotor face on both sides to remove brake pad film buildup.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat

Categories




Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN