brake hoses

[ghostflyer]

It’s 100 hrly time again . Checking on brake pads/parts etc and found my brake hoses very stiff to the point one snapped when I tried to bend it. The hoses are just over 4 years old . We had floods not long ago and the aircraft wheels went under for about 4 days . Replaced a heap of wheel/brake parts . Hoses inspected and found flexible then. BUT what I didn’t expect that the water soaked hoses had continued to deteriorate and the steel mesh was corroding and breaking down. So when do we replace the hoses and even give them a curious glance. I will now be checking them on every preflight as i do land on beaches on a regular basis . i wasn’t expecting the hoses to have such a short life.

[GAHorn]

In my experience, Aeroquip brake-line hoses last 20 years if the aircraft is hangared/covered. Stratoflex is similar. This is for braid-reinforced rubber-lined hoses in low-pressure applications such as brake lines, drain lines, and return lines. PTFE hoses have indefinite/extended life in such service. Checking them physically for dampness/leaks and stiffness is certainly a good idea.

As for firewall-forward and high-pressure flammable-fluid service and for emergency-applications (such as landing-gear emergency-extension, etc), 5 years is the recommendation for reinforced rubber lines and 10 years for PTFE hose.

A surprising number of firewall-forward, un-sleeved, low-pressure fuel lines (example: gascolator-to-carburetor) are 20+ years and frankly, this is disturbing to me. They should be firesleeved and changed every engine ovhl period… regardless of whether or not the engine is ovhl’d at the recommended time-period or not. (Our C145/O300 engines have 1800-hr/12-year ovhl times… which means our firewall-forward flammable lines should probably be timed-out at 12-years regardless of condition. I doubt many of us do that.)

[n2582d]

... Hoses inspected and found flexible then. BUT what I didn’t expect that the water soaked hoses had continued to deteriorate and the steel mesh was corroding and breaking down. So when do we replace the hoses and even give them a curious glance. I will now be checking them on every preflight as i do land on beaches on a regular basis . i wasn’t expecting the hoses to have such a short life.

I'm replacing the brake hose on my hangar neighbor's C-177. It's hard to believe, but this retired United B-787 Captain is even tighter than I am! Cleveland wheel/brake on the right side and McCauley on the left side. This brake line must be original from the factory -- stiff as a board. I was able to convince him it’d be best to replace the hose on both sides at the same time.

Aeroquip 303-3 hose is $12.60/ft. at Spruce. The hose ends are reusable (assuming they are airworthy) so there's little excuse to not replacing these hoses periodically. My guess is that the hoses attached to the master cylinder are more likely to need replacement than the ones at the wheel as they are a PITA to access and out of sight, out of mind.

PTFE hoses have indefinite/extended life in such service. Checking them physically for dampness/leaks and stiffness is certainly a good idea.

Various manufacturers and retailers caution against flexing these hoses too much as that could damage lines that have taken a set. AC43.13-1B Par 9-30, D, (1) says,

Although Teflon hose has excellent performance qualities, it also has peculiar characteristics that require extra care in handling. It tends to assume a permanent set when exposed to high pressure or temperature. Do not attempt to straighten a hose that has been in service. Any excessive bending or twisting may cause kinking or weakening of the tubing wall.

Regarding service life/replacement interval I've read quite a range of recommendations. Obviously a lot depends on the type of hose and the particular application. The shortest I've seen is Lycoming's recommendation of two year replacement for 601 type rubber hose used with low leaded avgas. Thinking of Ghostflyer's experience, I emailed Wipaire to find out what hose they use on their amphibious floats. What conditions could be more demanding on brake hose than that of amphibious floats? They use Aeroquip 2807 teflon hose, a type I hadn't previously heard of. He wrote, "These generally have not been susceptible to corrosion as described, it is usually the fittings that corrode first. We recommend coating them with any good anti-corrosion product." It looks like Aeroquip 190600 fittings work with this hose.

George, I think it's largely semantics, but your write,

This is for braid-reinforced rubber-lined hoses in low-pressure applications such as brake lines, drain lines, and return lines. ... low-pressure fuel lines ... .

When I think of low-pressure hose I think of Aeroquip 306 or Stratoflex 193 hose used for instrument and vacuum lines. I'm not sure how much pressure C-170 brake lines experience -- I've read around 600 psi -- but I would not use Aeroquip 306 or Stratoflex 193 low pressure hose for brake lines or fuel lines. Spruce calls Aeroquip 303 hose a mid-pressure hose. The maximum pressure for the smaller diameters of this hose is 3000 psi.

[GAHorn]

Gary, I feel you do me a disservice on both quotes of me.

In the first criticism you reference AC4.13 advice against checking flexibility of teflon hoses in “high pressure” service…while I was not specifically recommend teflon hose in this application …I can see where it might appear that my recommendation to check their health might have seemed directed at them. My comment was actually speaking of the common “braid reinforced rubber” hoses. Also the brake pressures in our airplanes is a LOW pressure application…not a hydraulically-boosted 2,000 psi system as might be encountered in larger corporate/airliners….so a caution against flexing hoses that have been subjected to HIGH pressure seems moot.

In the second criticism, I did not mention Aeroquip 306 hose so it’s not fair to criticize those comments. The reason i did not mention 306 is because it’s not designed for hydraulic fluid..it’s designed for air/pneumatics. Aeroquip 303 hose is designed for hydraulic fluid and is the most common found in brake lines in our airplanes…. I expect that is what folks will use since that is the type most appropriate.

And it is good practice in my opinion to check those types of braided, rubber-lined hoses for flexibility… regardless of what AC43.13 says regarding teflon hoses. When brake lines become stiff and inflexible they are simply getting old and should be replaced.

[cessnut]

Don't be running out and fabricating aircraft hoses from Aeroquip 2807. Wipaire's floats are TSO'd with that hose but it is not approved for other aircraft applications. It is also difficult to install those fittings properly if you haven't done it previously.

[n2582d]

In the first criticism you reference AC4.13 advice against checking flexibility of teflon hoses in “high pressure” service…while I was not specifically recommend teflon hose in this application …I can see where it might appear that my recommendation to check their health might have seemed directed at them. My comment was actually speaking of the common “braid reinforced rubber” hoses. ...
And it is good practice in my opinion to check those types of braided, rubber-lined hoses for flexibility… regardless of what AC43.13 says regarding teflon hoses. When brake lines become stiff and inflexible they are simply getting old and should be replaced.

Again George, I think this is largely a matter of semantics. The question is how much should one flex a hose when checking them; where is the line between bending and overbending flexible lines? Here's what one EAA article says:

A good basic condition check for both surplus and new or used hoses is to flex them to see if they have taken a permanent set. This is not a very scientific means of determining the condition but when hose flexibility is gone, so is much of its useful service life.

If you are still unsure about the condition of the hose, put it close to your ear and flex it. If you hear a crackling sound you can be assured that the hose is indeed becoming brittle and should be discarded.

One of the best resources I have found regarding aircraft hoses is AWB 02-066 published by Australia's Civil Aviation Safety Authority (CASA). There they write,

Both rubber compound and PTFE hoses can take on a permanent ‘set’ or shape (become less flexible) after some time in service. The inner liner can fail if flexed excessively or temporarily kinked during removal for testing for example, or while removing the hose or gaining access to remove and install another component. Do not attempt to straighten hoses which have a ‘set’ shape and maintain hose shape during pressure testing, as any curved hose will tend to straighten when under pressure. Consider handling PTFE hoses as if they are solid or rigid lines.

SAIB NE-06-67 recommends, "you caution maintenance personnel against overbending of those flexible lines and hoses and to treat them as hard lines. We also recommend that you inspect flexible lines and hoses that carry flammable fluids for kinks." But you're right -- I think this SAIB is about teflon rather than rubber hose.

Now, regarding types of hose, you wrote, "low-pressure applications such as brake lines, ... ." That caught my attention because I have never viewed brake lines on the C-170 as being low pressure. But, as you said, you are contrasting this to jet aircraft which see hydraulic pressures as high as 3000 psi. I've finally found a definition of low, medium, and high pressure as it relates to aircraft hose.

• Low pressure—below 250 psi. Fabric braid reinforcement.
• Medium pressure—up to 3,000 psi. One wire braid reinforcement. Smaller sizes carry up to 3,000 psi. Larger sizes carry pressure up to 1,500 psi.
• High pressure—all sizes up to 3,000 psi operating pressures.
Aviation Maintenance Technician Handbook, Chapter 9-16

[n2582d]

Don't be running out and fabricating aircraft hoses from Aeroquip 2807. Wipaire's floats are TSO'd with that hose but it is not approved for other aircraft applications. It is also difficult to install those fittings properly if you haven't done it previously.

Good advice. Here's a link regarding TSO standards for aircraft hose. But, to play the devil's advocate, using AC 23-27 couldn't one use Aeroquip 2807 because it meets or exceeds SAE 100R14A specifications? (SAE 100R14B specs. would be better because type B has the additional feature of an electrically-conductive inner surface to prevent buildup of an electrostatic charge. Apparently this electrostatic charge can make a hose into a something like a garden soaker hose). The Cleveland wheel/brake STC is not specific as to what sort of hose should be used:

[ghostflyer]

When I removed the brake hoses and end fittings, and thinking I'm could reuse the fittings , the outer fitting was found to be heavily corroded internally . The inner fitting was screwed out with no issues but the other fitting destroyed the old hoses as I was attempting to unscrew it .
A tip was given to me was coat the internal threads of the outer fitting with Boat wheel bearing grease before threading it on to the new hose. Even use the wheel bearing grease on the internal fitting threads minimally . I have done this and pressure tested the hoses to 1800psi for 24 hrs . No leaks .
I am NOT recommending this to you without consultation with your approved maintainer. Boat bearing grease is resistant to water.

[GAHorn]

Don't be running out and fabricating aircraft hoses from Aeroquip 2807. Wipaire's floats are TSO'd with that hose but it is not approved for other aircraft applications. It is also difficult to install those fittings properly if you haven't done it previously.

Good advice. Here's a link regarding TSO standards for aircraft hose. But, to play the devil's advocate, using AC 23-27 couldn't one use Aeroquip 2807 because it meets or exceeds SAE 100R14A specifications? (SAE 100R14B specs. would be better because type B has the additional feature of an electrically-conductive inner surface to prevent buildup of an electrostatic charge. Apparently this electrostatic charge can make a hose into a something like a garden soaker hose). The Cleveland wheel/brake STC is not specific as to what sort of hose should be used:Cleveland Conversion.png

Well…if Cleveland instructs us to “attach flexible…hose”…. to the rigid line… I kinda expect the hose to be flexible. I don’t know how to determine that upon inspection for cont’d airworthiness without checking it for flexibility. (After-all…what would be the advantage and purpose of a “flexible” hose if it were no better than the rigid line we’ve replaced with it?)

It’s a subjective matter, of course, but if flexing the hose causes it to fail…then, personally, I’d want it replaced. YMMV

(An interesting description of so-called “teflon” hose offered by Aircraft Spruce on their website seems to conflict with the earlier warning against flexing that type hose: “ Aeroquip 666 medium pressure Teflon™ hose is….. a lightweight hose able to withstand prolonged flexing and vibration under all service conditions. …” (emphasis mine)

[ghostflyer]

I was contacted by a ex member offering some advice on stopping these brake hoses corroding out . He told me to liberally coat the outer hoses with boat grease and then slip on some electrical plastic conduit over the fabric covered part of the hose and then clamp each end down with a worm drive hose clip. He claims it’s good for at least 12 months and inspect every 6 months . His Cessna 180 is constantly landing on beaches .

[Ryan Smith]

Dovetailing into this, I’m replacing everything in my first annual it would seem. I told my IA I don’t even went to put air in the tires before the next annual.

One of the hip bones connected to one of the leg bones in my airplane lead me into removing my rudder pedals and torque tube assembly which were all in quite sorry shape, unfortunately. I should have taken more better pictures, but I don’t want the associated judgement for flying an airplane around in that condition.

My master brake hoses were stamped 11/51 and 01/52, and imagine the rest of the hoses are of similar vintage. I’d like to replace all of my soft hoses on the assumption that they were last touched by a Wichita craftsman on a cold day in late February 1952.

My airplane is currently on jacks and I don’t want to add another wiggly 300 pounds to the problem, so I’m hoping someone has measured or has handy 0500106-12 and 0500106-13 (figure 58 items 12 and 13) to measure? I’m having Precision Hose Technology make a full new set of brake lines for me out of Aeroquip 666 equivalent (I haven’t gotten an answer if Stratoflex 124 or 156 is what they’ll use). I need the total length from the outside edge of each nut and the wrench size used. I can probably just give them what the end fits on to, but I’m sure the Fisher Price it down because they’ve had to remake enough stuff.

Any help is greatly appreciated.

Ryan

[c170b53]

I thought that those items (lines) were made from aluminium tubing, maybe you mean item #4 (flex lines). If original they will be as hard as rock with zero flexibility. There’s not alot of room there so the lines must fit precisely otherwise they will foul on structure. I’d wait till you can get in there fabricate one end then you can measure where the other end will end.

[Joe Moilanen]

I was paranoid about getting the wrong lengths also, so decided to remove every flexible hose on my plane, labeled them as what they were for, and sent them to Precision Hose to have them duplicated.

Joe
4518C

[cessnut]

Items 12 and 13 are rigid aluminum lines. On the topic of original rubber, the other day I was cleaning the shop and decided to dismount and discard the whitewall tires from the original Goodyear wheels on my '52. Out of curiosity I removed the tubes to check for a date stamp. 06-52. They are still soft and pliable and holding air. They have been out of service since 1977. I wish new tubes held up that well.

[DaveF]

On my airplane, all brake lines except for the master cylinder hoses (index 4) are aluminum. I replaced the two index 4 hoses with S1167-4-0100, Spruce part number 05-12083.