How to Block Off a Brake Line

Working on your brakes? Before you start disassembling your brake system, you’ll need to properly block off the brake lines. Blocking off brake lines prevents brake fluid from draining out and introducing air into the system. Follow this guide to learn how to safely and effectively block off brake lines for your brake repair or upgrade project.

Why Block Off Brake Lines?

When you open any part of the hydraulic brake system, brake fluid will drain out due to gravity and lack of pressure in the system. This can lead to:

  • Loss of brake fluid leading to low fluid level
  • Air getting sucked into the lines causing vapor lock
  • Brake failure due to lack of hydraulic pressure

Blocking off brake lines maintains system pressure, keeps fluid in, and prevents air intrusion. This allows you to work safely on other brake components without compromising the hydraulic system.

Prepare for the Job

Before blocking off brake lines, take preparatory steps:

  • Check compatibility – Ensure the block off method and materials are compatible with your brake line type and size. This varies by vehicle.
  • Support the vehicle – Use jack stands to lift and support the vehicle. Do NOT rely on a jack alone.
  • Protect painted surfaces – Use fender covers to avoid brake fluid damaging paint.
  • Have rags and brake cleaner ready – To soak up spills and clean components.
  • Wear eye protection – Brake fluid can harm your eyes.

Methods for Blocking Off Brake Lines

There are several methods you can use to temporarily or permanently block off brake lines.

Brass Union and Plug

Brass unions and plugs screw into the brake line fitting to maintain pressure. This method allows temporary block off for servicing other components.

Supplies needed:

  • Brass union with correct thread size
  • Brass plug for union


  1. Drain some brake fluid from the system.
  2. Screw in brass union where you need to block the line.
  3. Attach brass plug to seal off the union.
  4. Remove plug and union after work is complete.

This method works well for short term repairs but doesn’t permanently block off the line.

Rubber Hose and Clamp

For rubber brake lines, use a short section of matching size rubber hose and secure it with a strong hose clamp.

Supplies needed:

  • Rubber hose
  • Hose clamp


  1. Drain some brake fluid from the system.
  2. Slide hose section over the brake line end.
  3. Position hose clamp and tighten securely.
  4. Cut off excess hose when job is complete.

This creates a quick and reversible block off for rubber lines. Use fuel line rated hose and clamps.

DIY Block Off Plugs

You can make DIY metal plugs to permanently block off a line using basic tools.

Supplies needed:

  • Hammer
  • Hardened steel punch or bolt
  • Pliers
  • Vice grips


  1. Drain brake fluid from the system.
  2. Clamp line in vice grips.
  3. Use a hammer and steel punch to flatten the line end.
  4. Fold flattened end over and hammer again to seal off.
  5. Cut off excess length and deburr edges.

This crude but effective method permanently blocks off a line. Use caution to avoid cracking the metal line.

Brake Line Block Off Plugs

For permanent solutions, get purpose made brake line block off plugs. These thread into the line fitting and seal it off.

Supplies needed:

  • Brake line block off plug for your vehicle


  1. Drain brake fluid from the system.
  2. Apply thread sealant to block off plug threads.
  3. Thread plug into brake line fitting and tighten securely.

The plug will withstand brake system pressure and permanently deactivate the line. Match thread size carefully.

Bleeding the Brakes

After blocking off lines, bleed the brakes to remove any air introduced during the process:

  • Refill reservoir with DOT3 or DOT4 brake fluid.
  • Bleed starting with the wheel farthest from the master cylinder.
  • Bleed each wheel until no air comes out and fluid is clear.

Bleeding is crucial to prevent vapor lock and restore full braking power.

Safety Tips

  • Use jack stands and chock tires when working under a vehicle.
  • Wear eye protection when working with brake fluid.
  • Dispose of used brake fluid properly.
  • Avoid brake fluid contacting painted surfaces.
  • Check for brake fluid leaks after the job is complete.

Take safety seriously when blocking off and working on your brake system.

In Summary

Now you know how to safely block off brake lines using brass fittings, rubber hoses, DIY plugs or purpose made block off plugs. Always take the proper precautions when disconnecting your brake system. With brake lines securely blocked off, you can move forward with servicing your brakes worry-free.


Is it safe to drive after blocking off a brake line?

No, you should not drive after blocking off a brake line unless it is done temporarily with the brass union method. Permanently blocked lines mean that brake system is compromised and driving could be hazardous.

How difficult is it to make DIY block off plugs?

Making DIY plugs requires some mechanical skill and the right tools, but can be done with common items. Take care not to crack or puncture the brake line when hammering it shut.

Can I use vice grips instead of a hose clamp?

Vice grips are not recommended since they can crush rubber hoses over time leading to leaks. Use proper hose clamps in the correct size range for a reliable seal.

What happens if I get air in the brake lines?

Air in the lines leads to vapor lock and brake failure. This is why bleeding the brakes is so important after blocking off lines. Follow proper brake bleeding procedure to remove any air.

Do I need to add brake fluid after blocking a line?

Yes, add fresh DOT3 or DOT4 fluid to refill the reservoir after draining some out. Topping off compensates for the fluid that was drained and ensures proper level.

Comparison Table of Block Off Methods

Brass Union and PlugReusable, temporaryDoesn’t permanently deactivate
Rubber Hose and ClampWorks on rubber linesCan leak if clamp loosens
DIY PlugsVery permanentPotential to damage line
Block Off PlugsPurpose-made, secureLine is permanently disabled

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