brake plumbing, SN95 master, etc.

Topic: brake plumbing, SN95 master, etc. (Read 8222 times) previous topic - next topic

brake plumbing, SN95 master, etc.

Reply #30 – May 30, 2007, 09:58:41 PM

So, any real tech behind not using aluminum brake fittings? I understand that Al doesn't have a fatigue limit, but that doesn't mean it can't be used in this application.

brake plumbing, SN95 master, etc.

Reply #31 – May 30, 2007, 11:58:46 PM

Try asking Wilwood, Brembo, Tilton, or ask CVProducts or even Aeroquip or Goodridge. They can give you the scientific explanation.
D2

brake plumbing, SN95 master, etc.

Reply #32 – May 31, 2007, 12:20:09 AM

To the best of my knowledge, Earl's and Aeroquip both sell Al fitting without any warnings saying not to use them in high pressure hydraulic service.

Do they?

I understand the scientific reasoning behind why one might want to be wary of Al in high-stress applications, but it (along with many other materials without fatigue limits) are used as such in commercial applications.

What material are the steel pieces made out of 1018, 4130? Is the Al 3003, 6061, 7075?

brake plumbing, SN95 master, etc.

Reply #33 – May 31, 2007, 04:14:26 PM

i dunno. im not a metallurgist. are you?

if you want the physics equations of how much each pedal push will expand the fitting, how many expansions/contractions the fittin can handle before it will explode, and metallurgy of various hydraulic fittings, look em up on CC.

im in the buisness, and talked about this with many who have been in longer than i have. i also dug around for a while on CC, and found what i needed. dave merely pointed out the disadvantage of the aluminum fitting, and recommended a steel alternative.

brake plumbing, SN95 master, etc.

Reply #34 – June 01, 2007, 12:36:57 AM

I understand metallurgy, which is why I question the reason for not using Al fittings unless you are worried about corrosion.

I think there is a big myth about Aluminum's lack of a fatigue strength. Notice the two charts below. The first is for steel, the second for various kinds of Aluminum.

The fatigue strength for steels is ~50% of the ultimate strength.
Aluminum has no corresponding fatigue strength, although the strength at 10^8 is sometimes used. At 10^8, the "fatigue strength" from the charted metals is ~25-30%.

1018 (mild steel) has an ultimate strength of 64ksi (kilopounds per square inch), and a fatigue strength of 32ksi
4130 (chromoly) has an ultimate strength of 97ksi and a fatigue strength of 49 ksi
6061-T6 has an ultimate strength of 45ksi and and equivalent fatigue strength of ~11ksi
7075-T6 has an ultimate strength of 82ksi and and equivalent fatigue strength of 21ksi

Best case pure fatigue scenario for 7075 Al is that is has ~65% of the strength of mild steel after 100 million cycles. Not very good, but that is where the confusion begins. I don't know the average cyclical stress a fitting receives. I couldn't figure it out even if I knew the pressure from the hydraulic fittings - I would need an FEA program to figure out the stresses. Plus, what vehicle is going to see 100,000,000 panic stops? Zero. Zilch. Nada. As the number of cycles decreases, the performance of aluminum increases. At some point, 1018 and 7075 cross. The real hard part of the question is - are the Al and Steel parts designed the same? Are they the same part, or is the Al thicker.

So, you end up with a problem that is essentially unsolvable using back of the envelope methods. Thus, I would lean towards an empirical answer.

How many aluminum fittings have failed in hydraulic service? None that I know of.
Sounds like a poor way to solve a problem, but sometimes experience is the best proof.

brake plumbing, SN95 master, etc.

Reply #35 – June 02, 2007, 08:00:22 PM

I'm in no way a metallurgist (sp?) but I was in the Air Force although I only flew on C-130s as a radio operator. Every part that I could see where hydraulics run, was aluminum. Do they use a different type of aluminum? I know that's probably a stupid question but..............Just wondering why all the fuss about that fitting.

John

brake plumbing, SN95 master, etc.

Reply #36 – June 03, 2007, 09:18:38 PM

No fuss, use what you want.

brake plumbing, SN95 master, etc.

Reply #37 – June 03, 2007, 10:42:57 PM

Back brakes only run around 100 psi. I doubt that the fitting would fail.

Have you guys ever used solder to fix a brake line? Works great!