TheSamba.com :: View topic - Why do brake lines have to be hard and not flexible?

Sat Feb 16, 2013 2:55 pm

Why cant we use a flexible brake line on the entire system?
There is a fllexible hose at each tire, why cant we use a flexible hose on the entire car?
Maybe a Pex like tube? (pex is plastic water line used in home plumbing)
Pex has metal cornering guides to prevent kinking.
You could replace all the brake lines in a couple of minutes.

Sat Feb 16, 2013 3:07 pm

You loose a little pressure as the rubber flex hoses age, so that's why some people use the stainless steel flex lines to have a firmer pedal and more pressure at the brakes. The hard lines don;t collapse and loose pressure like the flex hoses.

The system will run a lot better with the hard lines in place.

Sat Feb 16, 2013 3:14 pm

And steel tubing is really cheap!

Sat Feb 16, 2013 4:13 pm

I think the main lines are metal because otherwise you would have to replace them every 5-10 years, same as the rubber lines.

This would be a pain to do!

Sat Feb 16, 2013 4:25 pm

And if you don't replace your rubber lines they don't start leaking but fail by becoming totally blocked, in my two cases It was at about 30+ years.

Sat Feb 16, 2013 7:00 pm

Copper nickel alloy lines are the best of both worlds.

http://www.austinhealeywood.com/brakestory.html

Sat Feb 16, 2013 7:58 pm

Like others have said, two main reasons. First, the steel tubing lasts longer, it doesn't deteriorate like rubber does.

Second, and probably more important, it is very difficult to get a rubber that will flex and bend, but not expand. You need SOME amount of flexible rubber line to allow the wheels to move with the suspension, but you want to keep it to a minimum. The rubber will expand with the brake fluid pressure, if ALL your brake lines were rubber, your brakes would feel spongy and soft, and you wouldn't get very good pressure at your brakes where you really need it.

A small amount of rubber line is a necessary evil, for flexibility, but only the bare minimum. Steel lines give you much better braking performance.

Sun Feb 17, 2013 6:26 am

[email protected] wrote: Why cant we use a flexible brake line on the entire system?
There is a fllexible hose at each tire, why cant we use a flexible hose on the entire car?
Maybe a Pex like tube? (pex is plastic water line used in home plumbing)
Pex has metal cornering guides to prevent kinking.
You could replace all the brake lines in a couple of minutes.

Would think it would take less to cut or put a hole in a line that was running under the car if it was pex...... funny though I just saw a kit that replaced the entire system with it,used gator style bits to male the hard angles and such.

Might be just fine in a rail / or where you can run the hose inside the car as much as possible

Sun Feb 17, 2013 6:35 am

You can only bend a metal tube so many times before fatigue cracks it open. The wheels see constant supension travel, so the tubes would need to bend the whole time.

Sun Feb 17, 2013 8:34 am

[email protected] wrote: Maybe a Pex like tube? (pex is plastic water line used in home plumbing)
Pex has metal cornering guides to prevent kinking.
You could replace all the brake lines in a couple of minutes.
I wasn't clear what PEX was until I looked it up. I think they used it for the hot/cold plumbing in my house. Here's a clip from a description of PEX on this site.
PEX can also expand and contract, making it resistant to bursting in cold weather. Although no water pipe material can totally resist solid, internal freezing, PEX's ability to give a little provides functionality not possible with hard copper or plastic.

If it expands, it is not something you want to use for brake lines as this will make your brakes "spongy".

You should realize that the same steel lines + reinforced rubber hoses have been used on Beetles since the 50's(?). They didn't have the newer plastics and nylons we have today.
Also, even with all the new plastics and such, brake lines and hoses should be DOT rated if they are to be used for brakes. Usually, this means they have to be made from PTFE which doesn't expand. On top of that, they are usually sleeved in kevlar and stainless steel for protection.

If you are really serious about flexible hoses for all brake lines, you will want to use a system already approved for use in brake systems (this is your life and your passengers lives we are talking about)... look at DOT approved braided stainless steel brake lines. Here's a reference:
http://www.classictube.com/products/stopflex-ss-braided-hose

I think you may find that it is cheaper to use the normal steel lines with braided hose in place of the rubber sections, instead of 100% braided SS hoses. These short segments of braided hose can be found at many VW parts houses already cut and terminated in the correct brake fittings.
http://www.pacificcustoms.com/mm5/merchant.mvc?Scr...ement-hose

Sun Feb 17, 2013 8:40 am

To answer your question we have to delve into basic hydraulic theory..fluid under pressure exerts force in all directions and follows the path of least resistence..this theory allows you to use fluid as an actuator for motion.The conduit for the fluid,in this case brake lines,has to be suffciently strong enough to handle all the pressure the system will exert on it..subsequently,brake lines are stiff..

Standard rubber brake hose use a rubber core, a cloth braid wrap for pressure protection which is captured by anothe rubber coating,fully DOT approved to handle the pressure applied to the hose in application.

Steel braid brake hose uses a rubber core and a steel braid jacket to provide pressure protection.They are often sold as a superior application and look very pretty.When bought by custom length they are often fabricated on site by the counter jockey..if certain simple proccedures arent carried out correctly during fabrication,failure is a result..and the cost is quite a bit more than the standard rubber lines as well..

Sun Feb 17, 2013 12:05 pm

Yes the steel braided lines really made a difference in the way the pedal feels. On my 356a felt, No sponginess at all with them, almost too hard, felt weird until I got used to them.

Sun Feb 17, 2013 12:55 pm

Danwvw wrote: Yes the steel braided lines really made a difference in the way the pedal feels. On my 356a felt, No sponginess at all with them, almost too hard, felt weird until I got used to them.

your results would be the same replacing the fatigued rubber hoses with new rubber hoses..