3. Brake Lines – Part 2

Let us discuss today on Bundy tube Flaring... !

Brake line flaring is a process that adds a “flare” (expand or open outward in shape) to the end of the brake line to ensure a leak-proof connection. Flaring makes the tubing wider at the end. As the tubing is wider at this point, the connection can slip in deeper and more easily.

The quality of the brake line flares is a crucial factor. Low-quality flares could cause brake fluid leaks, and there is a risk of brake failure due to the leakage.

Flaring Types:

• Double / JASO / SAE 45-degree inverted flare:

If your brake line looks like a tiny funnel going into the ID of the tubing, and the back side of the flare is at a 45 degree angle, then it is the SAE flare. This flare is a most used flaring in automotive. It has a male threaded tube nut that connects directly to the outside diameter (OD) of the flared tube.

Look in the port where the line goes. If the bottom looks like a volcano pointing up at you it is an SAE flare seat.

• DIN / ISO Bubble Flare:

If the end of the tubing looks like a button, and the back side angle of the flare is 90 degrees, than it is the DIN / ISO flare. You must use a nut with a "lead" for this flare.

This type of flaring used together with a male swivel nut, seals the bottom of a tapped and drilled hole ending in an angled end. Bubble flares normally allow for resealing, but they have a reputation for a limited lifespan, and you cannot recover them from the deformation that occurs during the first seal.

Look in the port where the line goes. If it looks funnel shaped going away from you it is a ISO flare seat.

• AN Flares or 37-Degree Single Flares:

These flares, often known for their incorporation in most non-British race cars, have a 37-degree single flare that you can combine with a nut to accept double flares. The 37-degree flare became standard during World War II for the use in army and navy aircrafts.

Important Tips:

• Never use a single flare on automotive components.
• Single flares are never allowed on steel brake lines.
• Recommended torque for the fitment of brake lines: 1.2 to 1.8 kg-m

Will discuss about Bundy Tube packaging requirements in our next session...

References:

1.  JASO M101 – Metal Pipes for Automobile Tubing
2.  JASO F402 – Automotive Parts – Flare Fittings
3. Website related to brake lines & Flaring