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October 13, 2026 4 min read
Roll control versus line lock. What’s the difference?
If you’ve spent any time around drag racing, hot rods, or manual-transmission performance cars, you’ve probably heard both terms.
Here’s the simple answer: roll control and line lock use the same basic principle—trapping hydraulic brake pressure in part of the braking system.
What changes is how that capability is used.
I have a Hurst Roll/Control installed in my car, so instead of just explaining it, I decided to show you exactly how it works.
A roll-control system uses an electrically operated hydraulic solenoid installed in the brake system.
You apply the brakes normally, activate the Roll/Control, and the solenoid traps the hydraulic pressure you’ve already created in the controlled brake circuit.
That last part is important:
Roll Control doesn’t apply the brakes for you. It holds brake pressure that you applied with the brake pedal.
Release the control, and normal brake operation resumes.
It’s a simple system once you see what’s actually happening.
In the video, I demonstrate the basic principle from several different camera angles, including a first-person view from behind the wheel.
The situation is one every manual-transmission driver understands.
You’re stopped on an incline. Your left foot is on the clutch, your right foot is holding the brake, and the transmission is in gear.
Take your foot off the brake and the car wants to roll backward.
With brake pressure applied, I press the Roll/Control button. The solenoid holds that hydraulic pressure, allowing me to remove my foot from the brake while the car remains stationary.
From there, I can demonstrate transitioning from the brake to the throttle and clutch without the car rolling backward.
Important: This demonstrates the operating principle of the system. Hurst describes Roll/Control as a momentary brake-holding device intended for racing applications. It is not a replacement for your parking brake, normal brake-pedal operation, or a factory hill-hold system.
Think of the Roll/Control solenoid as an electrically controlled valve in the hydraulic brake circuit.
With the system inactive, brake fluid flows normally and the brakes operate just as they normally would.
When you apply the brakes and activate Roll/Control, the solenoid closes and traps pressure in the controlled circuit.
That keeps those brakes applied after you release the brake pedal.
Release the Roll/Control button and the valve opens again, releasing the trapped pressure.
That’s really all there is to the basic principle:
Apply brake pressure → activate Roll/Control → pressure is held → release Roll/Control → pressure is released.
So where does line lock come into this?
The same basic type of hydraulic brake-holding system can be used for a different purpose.
“Roll control” describes the brake-holding function.
“Line lock” is the term most enthusiasts associate with holding the front brakes while allowing the rear wheels of a rear-wheel-drive car to turn.
And if you know drag racing, you already know where this is going.
Burnouts.
With the front brake circuit held, the rear tires can spin while the vehicle remains essentially stationary. That allows a driver to heat the rear tires without trying to hold the car in place using both the front and rear brakes.
I'll demonstrate exactly how that works in a separate video.
The system in my car is the Hurst Roll/Control, part number 1745000.
If you’re considering installing one, there’s an important detail to know before ordering:
The Roll/Control unit and the installation kit are sold separately.
This is the main electrically operated hydraulic brake-control system.
Check the Hurst Roll/Control on Amazon
Hurst also offers a separate installation kit containing brake-line hardware and fittings for compatible applications.
Check the Hurst Roll/Control Installation Kit on Amazon
The installation kit is intended for compatible SAE-thread brake systems. Don't assume it's correct for every vehicle. Check your particular brake system and the current Hurst installation instructions before ordering or installing anything.
As an Amazon Associate, I earn from qualifying purchases.
This isn't an accessory where I'd recommend guessing your way through the installation.
You're modifying the hydraulic brake system.
Brake-line routing, fittings, flare types, electrical wiring, mounting location and system bleeding all need to be correct.
After installation, the entire system needs to be inspected for leaks and tested carefully before the vehicle is driven.
Vehicle brake systems also vary considerably. ABS, diagonal-split braking systems and other configurations can affect whether a particular roll-control system is appropriate or how it must be installed.
Follow the manufacturer's instructions for your exact application. If you're not comfortable modifying a hydraulic brake system, have someone qualified do the installation.
I've been working on cars for more than 40 years, and one thing hasn't changed: sometimes the easiest way to understand a mechanical system is to watch it work.
That's why I used multiple cameras for this demonstration.
I wanted you to see what I'm doing behind the wheel, what happens when I take my foot off the brake, and what the car actually does when Roll/Control is activated.
Once you see that, the hydraulic explanation makes a lot more sense.
Now we've covered the roll-control side of the system.
Next comes the one everybody wants to see:
Line lock.
I'll demonstrate how the same basic brake-holding principle is used to hold the front brakes while allowing the rear wheels to spin.
Yes.
There will be smoke.
—Troy Kane
V-Twins to V-8s
40+ Years of Hands-On Automotive Experience
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