Brake Line Replacement

In the previous thread, it was explained to me that the purpose of having two different size brake lines is to increase the braking force at the caliper.

What would be the downside if the brake line is replaced with just one size, instead of two different size brake lines like the OEM?

The brake line that I need to replace is for the rear passenger side. The attached YouTube video illustrates the process. In that video, if you pause it at min 1:20, you will notice that about 2" of the bent brake line that gets screwed into the rubber brake hose is a bit thinner than the rest of the brake line. That very short, thinner section is probably 3/16" and the rest is probably 1/4". When they replaced the new brake line, the entire line was the same tube size, which appears to be 1/4". From what was explained to me, a special type of machine is required to replicate a brake line exactly as the OEM on that car, since that same brake line has two different tube sizes. So, as an alternative option, is it perfectly okay to do it the same way they did it, which is to disregard the two different tube sizes and just stick to one tube size? Also, is there any downside or safety concerns to doing it that way?

Furthermore, the tube nut (fitting) that would fit onto a 3/16" brake line would be a different size than the one that would fit onto a 1/4" brake line. So, how in the world were they able to fit in a tube nut that's suitable for a 1/4" brake line into the rubber brake hose? The fitting for that rubber brake hose is M10x1.0, which is the size that's suitable for a 3/16" brake line. I'm actually very confused.

I'm looking into purchasing a pre-flared brake line. There are domestic, Japanese, and European brake lines. I understand that the European brake lines are bubble flared. However, what is the difference between domestic and Japanese brake lines that are both double flared?

Furthermore, as an example, if we take a look at the attached Part # CNJ-312, which is a pre-flared Japanese brake line, both fittings are the same size. On the other hand, the attached Part # CN-312, which is a pre-flared domestic brake line, why does it have one fitting that is longer than the other one?

Thank you!

Cheers!

https://youtu.be/Zj3HfNOZsxI

The one thing that I can think of that differentiates the pre-double flared domestic brake line from the Japanese one is that the fittings are in SAE for the domestic ones whereas the fittings are in metric for the Japanese ones. FYI, the pre-flared brake lines are flared at both ends. I have attached a picture. What I still don't understand is why does the domestic brake line (Part# CN-312) have fittings that are different lengths whereas the fittings for the Japanese brake line are the same length.

You suggested that if making our own brake line, to use the same tube size line throughout. However, is there any downside or safety concerns to doing it that way as opposed to having two different tube sizes like the OEM?

As I mentioned in the previous thread, in the YouTube video I attached, they disregarded the OEM version of having two different brake line sizes and instead replaced the whole line with one size (as you are suggesting to do so), which appears to be 1/4". So, naturally, my question is, how does a fitting that is meant to fit on a 1/4" tube line be able to fit on the rubber brake hose that is designed to fit a fitting that's suitable for a 3/16" brake line? Keep in mind that the rubber brake hose that is connected to the caliper is designed to screw on a fitting that's suitable for a 3/16" line.

Thanks!

Cheers!

When diagnosing to find out where the brake fluid leakage was coming from, I filled up the brake reservoir and pressed on the brake pedal. When pressing on the brake pedal, the brake reservoir was losing fluid immediately. However, the leakage at the rear passenger side area didn't start until after five minutes later. So, my question is, if the brake reservoir was losing fluid right away when pressing on the brake pedal, why does it take a while before we actually see the leakage? Where is the fluid going until it starts to leak? I'm wondering if I have other issues with the brake system.

My understanding all along has been that using a compression union for brake lines is unacceptable, dangerous, and even illegal in many states. Hence, using a doubled flared brake line is the best method to use. Nonetheless, would a high-pressure compression union rated for 5,000 psi (Dorman part # 800-202) be perfectly safe and acceptable to use?

Thank you!

Cheers!

Hi,

I would not recommend using anything except a double flare with the correct fittings. A double flare tool is fairly inexpensive and easy to use.

When diagnosing to find out where the brake fluid leakage was coming from, I filled up the brake reservoir and pressed on the brake pedal. When pressing on the brake pedal, the brake reservoir was losing fluid immediately. However, the leakage at the rear passenger side area didn't start until after five minutes later. So, my question is, if the brake reservoir was losing fluid right away when pressing on the brake pedal, why does it take a while before we actually see the leakage? Where is the fluid going until it starts to leak? I'm wondering if I have other issues with the brake system.

Thanks!

Cheers!