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If you watched my video and knew what the button on my shifter was, you're probably an old-school gearhead.
If you didn't, here's what it does.
The button operates a line lock, also commonly called a roll control. It's a simple system that lets you hold the front brakes on while releasing the brake pedal.
And yes, that makes doing a burnout a whole lot easier.
A line lock uses an electrically operated solenoid installed in the brake hydraulic system.
The basic operation is pretty simple:
Step on the brake pedal and apply the brakes.
Press and hold the line-lock button.
Release the brake pedal.
The solenoid keeps hydraulic pressure trapped in the front brake circuit.
The front brakes stay applied while the rear wheels are free to turn.
Release the button and normal brake operation returns.
That's why you'll often see line locks used at the drag strip. You can hold the car in place with the front brakes while spinning the rear tires to heat and clean them before making a pass.
Suggested caption: The button on the shifter operates the line lock on my 1966 Impala SS.
They're essentially two names you'll hear used for the same basic system.
That's why I asked the question the way I did in the video:
One purpose. Two different names.
Depending on when you got into cars, what brand of equipment you used or who taught you, you may have always called it a line lock or a roll control.
Either way, we're talking about controlling brake-line pressure electrically.
The button itself isn't doing anything magical.
It's controlling an electric solenoid installed in the brake hydraulic system.
When the solenoid is activated, it prevents the hydraulic pressure you've already created with the brake pedal from being released from the front brake circuit. That keeps the front brakes applied even after you've taken your foot off the brake pedal.
Release the button and the trapped pressure is released, returning the brakes to normal operation.
It's a pretty simple idea—and that's one reason these systems have been around for so long.
Suggested caption: The line-lock solenoid installed under the hood of my 1966 Impala SS.
This came up quite a few times in the comments on my video.
They're two completely different things.
A line lock works with the braking system. It holds hydraulic pressure to the front brakes.
A trans brake works inside an automatic transmission, engaging components inside the transmission to prevent the car from moving while the engine builds RPM for a hard launch.
My 1966 Impala has a 4-speed manual transmission, so there's no trans brake hiding behind that button.
It's a line lock.
Convenience.
When you're using a line lock, you want the switch somewhere you can operate naturally without taking your hand away from where it needs to be.
On my Impala, the line-lock button is mounted right on the shifter.
And if you've noticed another button on the shifter ball, that's for something completely different: the car's Gear Vendors overdrive.
Maybe we'll make that the next quiz.
For a street-driven classic car?
No.
But that's not really the point.
If you're doing burnouts or taking the car to the drag strip, a line lock lets you hold the front brakes without keeping your foot on the brake pedal and fighting the rear brakes at the same time.
It's one of those old-school pieces of performance equipment that's simple, effective and still works today because it doesn't need to be complicated.
Line-lock kits are readily available and can be added to many performance and classic-car brake systems.
If you're thinking about installing one, I've linked a line-lock kit below.
Product: Hurst Line Lock/Roll Control
Button/link: Shop the Line Lock Kit Here
As an Amazon Associate, I earn from qualifying purchases.
Important: Any modification to a vehicle's braking system needs to be installed correctly. Follow the manufacturer's instructions for the specific kit and brake system you're working with.
I knew plenty of experienced gearheads would recognize the system immediately.
What I didn't expect was how many different answers we'd get.
Line lock. Roll control. Trans brake. Nitrous. Trailer brake. Ejector seat. Flux capacitor.
Apparently I've got more buttons to explain.
If you knew what this one was, let me know in the comments.
And if there's some oddball part, tool or piece of old-school automotive technology you'd like me to cover next, send it my way.
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This site documents real builds, tools, and shop work from my own projects. Some pages are showcases. Some are how-tos and tool reviews. If you’re working on a project and want experienced guidance, I offer one-on-one coaching.