3. Brake Lines – Part 3

Let us go through the Bundy tube Packaging Requirements today in this last article on “Brake Lines”...!

Brake line or Bundy Tube routing is the most important and critical activity in brake design process. Logical routing of the brake lines can provide just the right amount of clearance around the engine compartment and chassis components, tucking them neatly out of the way where they will not become damaged. It is like playing the “Hide & Seek” in vehicle architecture.

Brake lines runs throughout the vehicle along the length and breadth, without fouling to any part. All this is a “acrobat” kind of activity for a brake designer.

Besides flares, brake lines also have bends.... lots of bends. It is possible to bend brake lines on your own. All you really need is the proper tube-bending tools; however, figuring out just where to bend the lines and how far to bend them can be rather tricky. It takes a lot of patience to make a brake line accurately connect to a specific brake part.

To save time, a OEMs (Vehicle manufacturers) rely on pre-bent brake lines. These brake lines come pre-measured and pre-bent in all the right places to specifically fit your vehicle. Pre-bent brake lines take less time of the installation process because they are already flared and bent for the best possible route through your vehicle.

In short, it is quite easy to design other brake parts than routing a brake lines in the vehicle.

With all these aspects, let us see some important Bundy tube routing Rules:

 1. Distance between two clamps for Brake line clamping:

Distance between two clamps should not be more than 350 mm measured along the Bundy tube routing.

More distance than this may cause overriding of brake lines, fouling with surrounding parts, sagging of brake pipes, and rattling of brake pipes.

2. Centre distance between two parallel brake pipes:

Centre distance between two parallel brake pipes should not be less than 12 mm.

This is applicable to ? 4.76 mm brake lines. Considering bending radius and other tolerances, 12 mm. Centre distance is required to ensure 3 mm. clearance in extreme condition. If this distance is not possible due to packaging constraint, then separator or clamp should be provided.

Insufficient Centre distance between two brake lines routed parallel may result overriding or fouling.

3. Minimum clearance of Brake pipe with Heat Source and flexible parts:

Minimum clearance of Brake pipe with Heat Source is extremely important as vaporization of brake fluid leading to increase in brake pedal travel.

Suitable “heat shield” to be provided, if above clearance cannot be meet.

4. The gap between Bundy Tube coupling nut and underbody:

Minimum distance required between Bundy Tube coupling nut and underbody is 15 mm. to easy access of brake lines during torqueing / fitment on production line as well as from the service point of view.

Less gap may result in difficulty in assembly and disassembly of Bundy tubes.

5. Brake pipe routing should not cross “MAX” mark on Brake fluid reservoir:

Facility of vacuum bleeding may not be available in service, hence manual bleeding required to be done. Brake pipe routed above “MAX” mark level will require sufficient pumping to be done to overcome the gravity effect for proper brake bleeding.

If brake bleeding is not done carefully, there were chances of air pockets formation.

Improper bleeding results in spongy brake feel & increase in stopping distance.

Note:

1. These are "thumb rules", may not be written anywhere.
2. Figures for clearances / gaps provided in the article may vary based on the individual experience in brake line routing.

References:

1.     Websites related to brake lines.

2.     Work experience with brake line routing.