Upgrading brake lines?

[mrblaine]

Well...

Decided to be a guinea pig and try it out. Replaced all 5 hoses with stainless braided, specifically goodridge branded hoses for the three main ones, and Wilwood hoses for the rear axle hoses.

The results?

It actually is fairly noticeable. Not as much in brake pedal travel, but moreso in the firmness of the pedal once the brakes are engaged. The amount of pedal deadband before the brakes engage is pretty much unchanged. But once the brakes are engaged, it doesn't take quite as much movement to modulate the brakes. It's not a particularly large difference, and isn't going to compensate for bigger issues. But it does seem to improve the sensitivity of the pedal.


The only other change that could possibly affect anything I have done would be to flush with DOT4 LV fluid instead of DOT4. (Low viscosity has a very slight improvement in theory; mostly just used it because it was as cheap as regular DOT4.) However, the difference it makes on non-ABS vehicles is nearly immeasurable, so presumably the main difference is the brake lines.

You're a testing guy. Do a simple test and afterwards you'll figure out that (a) either your existing lines were deficient, (b) you're dealing with confirmation bias. The test is simple and I did it at higher pressures than most can generate. I have a vacuum booster system in Kat's rig that is capable of 2800 psi. I hooked up a Goodridge SS braided line to the system and used a pair of very nice calipers to measure the relaxed and expanded diameter between 0 and 2800 psi. Then I did the same to a new OEM rubber flex hose. They both expanded exactly the same amount under the same pressure which sorta makes sense since the design burst pressure for both is typically in the 3000 psi neighborhood.

The other thing that will produce a similar effect to what you are experiencing is modern masters entrain air into the fluid during manual bleeding. After testing and breaking in on a new system, we always go back the day after and do a 1 or 2 pump bleed at each corner. That has never not gotten out that last little bubble of air that settled out of the fluid.

 

[Steel City 06]

You're a testing guy. Do a simple test and afterwards you'll figure out that (a) either your existing lines were deficient, (b) you're dealing with confirmation bias. The test is simple and I did it at higher pressures than most can generate. I have a vacuum booster system in Kat's rig that is capable of 2800 psi. I hooked up a Goodridge SS braided line to the system and used a pair of very nice calipers to measure the relaxed and expanded diameter between 0 and 2800 psi. Then I did the same to a new OEM rubber flex hose. They both expanded exactly the same amount under the same pressure which sorta makes sense since the design burst pressure for both is typically in the 3000 psi neighborhood.

The other thing that will produce a similar effect to what you are experiencing is modern masters entrain air into the fluid during manual bleeding. After testing and breaking in on a new system, we always go back the day after and do a 1 or 2 pump bleed at each corner. That has never not gotten out that last little bubble of air that settled out of the fluid.

Those are indeed possibilities.

The actual difference in travel seems to be fairly small, and I don't think we'd really get any more than the 1/4" I previously calculated. The noticeable difference is moreso in the stiffness of the brake pedal once engaged, almost that it is more twitchy (in a positive way) than before. (Which could also be explainable by an air bubble, but that system has been flushed several times through in separate occasions already.)

Unfortunately the vast majority of studies on the matter of brake hose volumetric expansion are paywalled, though there are a few snippets we can pick up on:

https://www.sae.org/publications/technical-papers/content/760296/
Paywalled, but an excerpt from Google Scholar noted:
… BRAKES HOSES Tests showed that steel braided hoses were vastly superior to production hoses … The hose expansion per foot of hose for 1000 psi was .005 cu. in. compared with .020 …

https://www.researchgate.net/public...teel_Braided_Reinforced_Teflon_Aviation_Hoses
Non-paywalled, but a preprint. Has some good discussions on the effects of braid angle and amount of steel wire used on the expansion (aka "capacitance") of brake hoses

https://scholar.google.com/scholar?...9#d=gs_qabs&t=1749173601238&u=#p=d_eJSUtNpTIJ
Sort of hard to follow this one, but I did note the following excerpt:

https://repository.tudelft.nl/file/File_242f64f6-52a3-4397-891a-c6ba299662fc?preview=1
This one is fairly interesting, mainly regarding their use of a stainless brake hose to assist in increasing the pulse frequency of an ABS system.

 

[mrblaine]

Those are indeed possibilities.

The actual difference in travel seems to be fairly small, and I don't think we'd really get any more than the 1/4" I previously calculated. The noticeable difference is moreso in the stiffness of the brake pedal once engaged, almost that it is more twitchy (in a positive way) than before. (Which could also be explainable by an air bubble, but that system has been flushed several times through in separate occasions already.)

Unfortunately the vast majority of studies on the matter of brake hose volumetric expansion are paywalled, though there are a few snippets we can pick up on:

https://www.sae.org/publications/technical-papers/content/760296/
Paywalled, but an excerpt from Google Scholar noted:
… BRAKES HOSES Tests showed that steel braided hoses were vastly superior to production hoses … The hose expansion per foot of hose for 1000 psi was .005 cu. in. compared with .020 …

https://www.researchgate.net/public...teel_Braided_Reinforced_Teflon_Aviation_Hoses
Non-paywalled, but a preprint. Has some good discussions on the effects of braid angle and amount of steel wire used on the expansion (aka "capacitance") of brake hoses

https://scholar.google.com/scholar?start=20&q=braided+brake+hose+expansion+&hl=en&as_sdt=0,39#d=gs_qabs&t=1749173601238&u=#p=d_eJSUtNpTIJ
Sort of hard to follow this one, but I did note the following excerpt:
View attachment 621518


https://repository.tudelft.nl/file/File_242f64f6-52a3-4397-891a-c6ba299662fc?preview=1
This one is fairly interesting, mainly regarding their use of a stainless brake hose to assist in increasing the pulse frequency of an ABS system.

All I know is what I tested and discovered. They are asking to accept that our rubber power steering hose is somehow less effective due to the rubber it has and at the pressures they operate at, it simply isn't the case.

 

[astjp2]

Another metric would be pedal distance for a given pressure, pisson ratio might be a factor that is very hard to measure, the only thing I can think of is how far the pedal goes down?