How the Parking Brake Works on Vehicles with Rear Disc Brakes

It’s applied by a mechanical actuator—either a small “drum-in-hat” shoe brake inside the rear rotor or a caliper-integrated screw/lever mechanism—operated by a cable or an electric motor (electronic parking brake). In modern cars, both approaches are common, with the actuation done mechanically to hold the vehicle even if hydraulic pressure bleeds off.

Why Rear Disc Brakes Need a Separate Holding Mechanism

Service brakes are hydraulic and designed for dynamic stopping, but hydraulic pressure can dissipate over time and cannot guarantee a vehicle will remain stationary. Parking brakes therefore rely on a purely mechanical lock that maintains clamping force without continuous hydraulic pressure. On rear disc-brake cars, this is provided either by a dedicated miniature drum brake inside the rotor or by a mechanical drive built into the caliper.

The Two Main Mechanical Designs

“Drum-in-Hat” (Drum-in-Disc) Parking Brake

Many vehicles with rear discs include a small drum brake integrated into the rotor’s hat section. When you pull the lever, press the pedal, or activate the switch, a cable or electric actuator spreads the internal shoes against the drum surface, holding the wheel. This design isolates the park-hold function from the disc caliper, tends to provide robust holding on steep grades, and can simplify servicing because the parking system has its own friction surfaces.

Caliper-Integrated Mechanical Actuator

Other models use rear calipers that incorporate a mechanical screw/ball-ramp and lever. A cable or electric motor rotates the mechanism, which drives the caliper piston outward to clamp the disc. This consolidates parts and saves space; the same pads provide both service braking (hydraulic) and parking-hold (mechanical), with an internal adjuster maintaining proper pad-to-rotor clearance.

Electronic Parking Brakes: How Modern Cars Apply the Hold

Electronic parking brakes (EPBs) replace the hand lever with a switch and add an electric actuator. Two architectures are prevalent; the differences lie in how the motor applies the mechanical force that a cable once provided.

• Motor-on-caliper: An electric motor and gearbox sit on each rear caliper, turning the internal screw/ball-ramp to clamp the pads onto the rotor.
• Central motor with cables: A single electric actuator pulls conventional cables that either spread drum-in-hat shoes or move caliper levers.

Both EPB types remain fundamentally mechanical at the wheel end; electronics simply provide the force and add features like auto-apply at shutdown, auto-release when driving off, and hill-hold integration.

What Happens When You Apply the Parking Brake

Regardless of the specific design, the actuation path is similar. The following sequence outlines the essential steps from driver input to wheel hold.

1. Driver input: You pull a lever, press a foot pedal, or tap an EPB switch.
2. Mechanical force generated: A cable is tensioned or an electric motor turns a gearbox to create mechanical force.
3. Actuator engages:
   – Drum-in-hat: The cable/actuator spreads the shoes against the rotor’s internal drum.
   – Caliper-integrated: A lever-driven screw/ball-ramp pushes the caliper piston to clamp the disc.
4. Self-locking hold: The mechanical geometry (screw threads/ramps or shoe anchors) holds the force without hydraulic pressure.
5. Adjustment and release: Internal adjusters maintain correct shoe/pad clearance; releasing the lever or switch removes the mechanical force.

This sequence ensures a reliable, purely mechanical hold so the vehicle remains stationary even if hydraulic pressure decays or the engine is off.

Pros and Trade-offs by Design

Automakers choose between drum-in-hat and caliper-integrated systems based on cost, packaging, and performance. Each has strengths and compromises.

• Drum-in-hat: Strong static holding, independent wear from service pads, often better for heavy vehicles or steep-grade parking; adds parts and requires periodic shoe/drum service.
• Caliper-integrated: Fewer components and simpler packaging; pad wear from frequent EPB use can increase, and mechanisms need clean operation to prevent seizing.

In practice, both designs are safe and effective when maintained; EPB overlays add convenience and automated functions without changing the underlying mechanical principles.

Maintenance and Diagnostic Notes

Proper maintenance ensures consistent holding force and prevents seized mechanisms, especially in corrosive climates.

• Inspect cables, levers, and bell cranks for corrosion, fraying, or binding; lubricate pivot points as specified.
• For drum-in-hat, check shoe thickness and drum condition; adjust if applicable.
• For caliper-integrated systems, use correct service procedures and tools to retract wind-back pistons; avoid forcing them.
• On EPB cars, follow scan-tool procedures for service mode and pad replacement; recalibrate after work.
• Watch for warning lights, uneven holding on slopes, or grinding noises—common signs of maladjustment or sticking components.

Routine checks during brake service and adherence to manufacturer procedures preserve performance and extend component life.

Summary

On vehicles with rear disc brakes, the parking brake is applied mechanically—either by a drum-in-hat shoe assembly inside the rotor or by a caliper-integrated screw/lever that clamps the disc. Modern models often use an electric motor to drive these mechanisms, but the wheel-end action remains mechanical to ensure a reliable, long-term hold without hydraulic pressure.

How is the parking brake applied on vehicles equipped with rear brake calipers?

On vehicles with rear disc brakes, a parking brake is applied by a mechanical cable, electronic actuator, or internal drum brake system that acts on the caliper, either by squeezing the pads directly or by expanding shoes within the rotor hub. A lever or foot pedal (or electronic button) pulls a cable or sends a signal, which forces the brake pads against the rotor to hold the vehicle still. 
Mechanical Systems

• Direct caliper action: Opens in new tabIn this common type, the parking brake cable pulls a lever on the caliper, which then actuates a mechanism (like a screw or cam) that pushes the piston against the rotor’s brake pad. 
• Integrated drum-in-hat system: Opens in new tabSome disc brake systems use a small drum brake located inside the rotor’s hub or “hat”. The parking brake cable expands these internal brake shoes against the inside of the rotor, holding the vehicle stationary. 

Electronic Systems 

• Electric Parking Brake (EPB): Many modern vehicles use an electronic system where a push button activates a small motor on the brake caliper. This motor then squeezes the brake pads against the rotor, or an internal cable actuator tightens the cable to the caliper.
• Smart “Park”: Some vehicles will automatically apply the electronic parking brake when shifted into park.

How the Action Works

1. Engagement: When you apply the parking brake (pulling the lever, pressing the button, or using the pedal), you activate the mechanical cable or electronic actuator. 
2. Force Transfer: This mechanical or electrical force is transmitted to the caliper or the drum-in-hat system. 
3. Brake Application: The caliper’s piston is pushed, or the drum brake shoes are expanded, applying pressure to the brake rotor. 
4. Stationary Vehicle: This friction holds the wheels stationary, acting as the parking brake. 

How does a typical parking brake function on a vehicle equipped with rear drum brakes?

The steel cables are attached to the parking brake, and when the parking brake is pulled, the steel cables are tightened. Most vehicles have drum brakes on their rear wheels; so, when the parking brake is pulled, the cables will pull a lever that compress the brake shoes to stop the vehicle.

What are the two most common types of parking brake apply mechanisms?

The two most common types of parking brake apply mechanisms are mechanical and electronic. Mechanical systems use a hand lever or foot pedal to pull a cable that engages the brakes, while electronic systems use electric motors to activate the braking mechanism, offering different engagement methods like button-activated systems.
 
Mechanical Parking Brakes

• How they work: This traditional type of parking brake relies on a physical cable connected to a hand lever or foot pedal. When the driver operates the lever or pedal, the cable is pulled, which then clamps the brake pads against the rotor (in disc brakes) or pushes the brake shoes against the drum (in drum brakes), holding the vehicle in place. 
• Common in: Most older vehicles and some newer ones still use this reliable, entirely mechanical system. 

Electronic Parking Brakes (EPB) 

• How they work: Instead of cables, EPBs use electric motors to apply the parking brake. There are two main variations: 
  • Caliper-Integrated System: The motor is built directly into the brake caliper assembly. 
  • Cable-Pull System: An electric motor pulls or releases the cables of a traditional parking brake system. 
• Common in: Modern vehicles, where they are often activated by pressing a button or switch, providing a more convenient and sometimes more powerful parking brake. 

How does the parking brake work on disc brakes?

On a disc brake system, the parking brake mechanically actuates either a secondary drum brake assembly located inside the rear rotor hub, or it uses a corkscrew-like mechanism within the main caliper to mechanically push the pads against the disc. This bypasses the normal hydraulic system, using mechanical cables to engage shoes or a piston, applying pressure to the rotating disc or internal drum to lock the wheel.
 
This video shows how parking brakes work on disc brake systems: 1mVehicle EngineeringYouTube · Sep 8, 2020
How it works

1. Bypassing the Hydraulic System: The parking brake is a mechanical system, not a hydraulic one, so it can function even if the main hydraulic brakes fail. 
2. Cable-Driven Actuation: A hand lever or foot pedal is connected via cables to the rear wheels. 
3. Two Main Designs:
   • Drum-in-Hat System: A small drum brake is built into the center hub of the rear brake rotor. When the parking brake is engaged, the cables pull on levers that activate small brake shoes, which expand and press against the inside surface of the drum, stopping the car. 
   • Caliper-Actuated System: In this design, the mechanical linkage from the parking brake cable operates a mechanism within the brake caliper itself. 
     • This mechanism uses a corkscrew or screw-and-lever system. 
     • When the parking brake is pulled, the lever pushes a piston into the brake pads, forcing them against the brake rotor. 
4. Self-Locking Mechanism: The lever or pedal has a ratchet mechanism that locks in place to hold the brake applied until the release button is pressed. 

This video explains how a drum-in-hat parking brake works: 46sCodyYouTube · Jan 7, 2017
In summary
Regardless of the type, the mechanical linkage of the parking brake uses a different force than the primary hydraulic system. It applies pressure to the brake components (either inside a drum or via the caliper) to hold the rear wheels in place.