Brake Line Replacement

Great question. The reason for the two different size lines is to increase the braking force at the caliper.

So when you take a larger line to a smaller line and push fluid through it the pressure is larger coming out of the end of the line.

Think of a garden hose that you put your thumb over.

I think if you are going to splice in a replacement line then you need to replicate the step down in line size if this is where the leak is.

I would not suggest trying to do this yourself as it requires a specific machine to make this line. So if this is where your leak is, I would go to a salvage yard and get this entire brake line and then just cut off the same portion on that one that you need to replace on your vehicle.

Then use this guide to join them that walks you through how to make a brake line:

https://www.youtube.com/watch?v=sO43p4ZFUiM

I attached the picture below of where I would cut it (#2) and then disconnect the joint at number 1. If you cut it at number 2 then you save yourself some bending.

Let us know if you have questions on this. Thanks

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

This is what I would do. If making your own brake line, I would just use the same size line throughout.

I do not see any difference in the different markets so I can only think that this is just a classification to meet different standards per the different markets.

Also, the reason for the different size fittings is so that you have both options. I suspect the other end of this line is not flared so you can just slide those fittings off. Normally these 12 in lines are flared at one and the other end is not so that means you can bend it to the point you need, cut the rest off and then flare the other end.

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!

Understood. There are no safety issues because the only thing that will happen is more fluid will leave the reservoir to fill the larger line.

Also, to make the different line sizes fit, I would just replace the rubber line so that the fittings are all the same. Otherwise, you are back to using an OEM line that has the reduction.

As for the different lengths of the fittings on this replacement line, they are different just because there are some that require the longer threads, so they provide that on one end. Keep in mind, these are universal, so they need to try and fit as many different vehicles as possible.

If you don't require the longer threads, then it is fine to use them any way. They seal the same way but if you only have two of the shorter fittings then you will have leaks because it is not going to bottom out on the female end.

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!

This is a great question. However, we need to get a new post started so that others can find the solution and they possibly won't find a leak issue under this heading, and we want to make sure all can find this one.

https://www.2carpros.com/questions/new

If you can also include in that post, how much fluid is leaving the reservoir (mark the top of the fill mark and then mark the line it drops to.

Also, when you press the brakes, do they drop to the floor? lastly please include if the fluid returns to that fill mark when you release the brakes.

Let us know and we can get back to you on this. Thanks