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Question about automotive braking systems

Question about automotive braking systems

Question about automotive braking systems

This may not be the proper place to ask this so forgive me if wrong. Can someone direct me to the Federal Reg that "specifically" dictates that hydraulic braking systems MUST have 45 deg. "double" flare connections?

I'm involved in a protracted forum thread regarding 45 deg double flare on automotive hydraulic braking systems and if it is indeed a DOT requirement.

Thanks so much

RE: Question about automotive braking systems

The 45-degree double flare is no where mandated by any Federal document. However, if you are building brake components in the U.S. that will be sold in interstate commerce, the long are of the law in the form of the DOT Federal Motor Vehicle Safety Standards come into play. For example, if you look at FMVSS 106, which is the DOT standard for automotive brake hose, you will find references to various SAE specs, which if you follow the train long enough, will get you to components like rigid steel brake tubing and fittings that incorporate the 45 degree flair. The DOT standards, like their SAE counterparts have labeling and performance requirements for components like brake hoses. You will need to have that DOT and/or SAE label as proof of conformance to the standards. As the 45-degree double flare has a long history of satisfactory usage in brake applications it would be wasteful for a potential supplier to chose some other system, such as AN 37 degree single flare. It will also be costly, as the potential supplier will have to qualify his system with testing at certified labs in order to get the DOT seal of approval. Why go to the extra trouble when you can use the tried and true 45-degree double flare readily available for any brake line component? Now if you are just building your own kit car, you can use any tube flare system that strikes you fancy, unless your state DOT has other thoughts.

RE: Question about automotive braking systems

Thanks so much for the reply. Some of the builders in this forum I belong to state that they use AN 37 deg on brake systems. Do you think the AN 37 deg, with tube sleeve, is sufficient to hold the requirements of an automotive brake system? If it's just your opinion, that's fine.

RE: Question about automotive braking systems

AN 37 degree fittings with the proper sleeve will be fine for the pressures encountered in an automotive brake system.

RE: Question about automotive braking systems


RE: Question about automotive braking systems

I'm curious what the context here is; racing only? I ask because I'm aware of many owners of Porsches having their cars fail state or provincial inspections with aftermarket SS-braided lines (using standard 45-deg fittings) that do not have a DOT/SAE labels. I can't imagine these AN systems passing such an inspection. I've also heard of insurance companies rejecting claims where such non-labeled lines were installed and braking performance "could" have been a factor, even with no failure of the lines. (Context here is single-vehicle incident with loss of a high-dollar car)

RE: Question about automotive braking systems

Either you follow 37° or 45° flare design, correct tighening torque will ensure sealing of the joint.

RE: Question about automotive braking systems

There are all sorts of proprietary tube fitting designs besides 45deg and 37deg, including connections for 20-30Kpsi fluid systems.

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