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Brake pad backing plate types

What is a brake pad backing plate?

In a disc brake design the friction material, also called a friction block or “puck” is attached to a steel brake pad backing plate with rivets, adhesive, or a newer NRS™ mechanical retention system. The backing plate is made from steel and transfers force from the brake caliper piston evenly across the backing plate to apply the friction material to the brake rotor.

 

brake pad attachment technology

Riveted brake pads—the oldest and least reliable bonding method

Drilling or stamping holes in the steel backing plate weakens

riveted brake pad

Riveted brake pads fail due to stress from flexing and damage to the backing plate cause by heat/cooling

it and causes it to flex under pressure. That flexing, along with rust formation causes the friction material to crack and separate from the backing plate. Few manufactures still use rivets for disc brake pads.

Matrix and In-mold brake pads

In-mold techniques are also used to bond the friction block to the backing plate. Holes and patterns are stamped into the steel backing plate and the plate is then coated with adhesive. The plate and the raw friction material are placed in a press and squeezed together under tremendous heat and pressure. The pressure forces the friction material through the opening in the backing plate. The friction block is retained with adhesive and the mechanical contact with the backing plate openings.

in-mold brake pad bonding

NRS™ Retention

NRS backing plates use a variation of the in-mold process. But the plates don’t have openings. Instead they have hooks that embed into the friction block as the raw material is forced into the mold. In addition to the hooks, NRS backing plates are made from high quality galvanized steel.

What goes wrong with a brake pad backing plate?

High quality brake pads use a top quality steel that’s stamped

brake pad backing plate

GBSC tests show that black steel backing plates rust and change dimensions

to exacting specifications. However, lower quality brake pads often use low quality “black steel” that’s coated with iron oxide, or “mill scale.” The mill scale must be removed before the friction block can  be bonded to the backing plate. To save money, some brake pad manufacturers shot blast the backing plates to clean them. Unfortunately, shot blasting can deform and compromise the backing plate’s critical dimensions. Once compromised, those altered dimensions can affect fit, function and even safety when installed on the vehicle.

Once the friction block is bonded, those manufacturers paint the steel backing plate to prevent corrosion. As you know, paint, even power coated paint, can’t stand up to the heating/cooling cycles found in all braking systems. The paint eventually fails and the steel starts to corrode.

Rust jacking destroys brake pads

As rust takes over and grows, it exerts force against the friction block, causing “delamination” and cracking. In other words, the growth of rust is more powerful than the bonding force of the adhesive.

NRS™ is a Trademark of NuCap Corporation.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat

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