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FlyinTiger

Well Known Member
Going through my "new to me" RV-4 built in 1994, it was made clear to me that I should replace the plastic brake lines at least up to the firewall with aluminum tubing. As the brakes heat up on those down hill taxi ways the plastic lines can soften from the heat, allowing brake fluid past the line and saturating the brake pads while letting air into the system. Unfortunately this happened to me on the right side the second time I taxied out to the runway.

Biggest challenge on this project? Getting the gear fairings off...they probably haven't been off in quite a while and the pins were pretty well set in place. I sprayed parts of the piano hinge I could get to with silicon lubricant, twisted the wire to work it in and then proceeded to work out the pins. One side was much more stubborn than the other.

Thanks to Ed Martinson for the help getting a list of parts so I could get this right without several trips to the local parts store.





 
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The old...

Plastic lines probably work all right for those on grass strips or level airports. Several down hill landing strips out here in the foot hills. With the fixed pitch cruise prop the -4 likes to taxi pretty fast and I'll feel better about hitting the brakes more than once in a while to slow her down.

Here's the old lines and insulation:





 
And the new...

After getting some pointers from the local RVAtors group (Ed) I felt confident putting things back together myself. Dave L. loaned me a flaring tool, tubing bender and some spare tubing to practice on. The first leg took me two hours, the second leg only one hour...go figure.







 
the transition...

I decided to transition from aluminum to plastic tubing along the firewall next to the motor mount. It seemed to be a logical place to secure the tubing where it would be out of the way and in a straight line.

It was recommended that I put the tubing on the front of the gear legs in case I decide to put the wood dampeners on the back of the gear legs at a later date. I'm going to hold off putting on the wood to see if the main gear shimmy is an issue once I get some stick time under my belt. One way to keep the shimmy to a minimum is to taxi slower. I've heard tire air pressure has something to do with it as well.

If anyone sees anything worth commenting on or has a recommendation, experience or other thing to share, please do!

 
Hinge pin removal

The next time you need to remove a stubborn hinge pin, just bend the end straight and chuck it up in a drill. Spin it while you pull and it will easily come out . That's how I got my gear fairings off.
BTW, I'm replacing my brake lines with braided stainless steel hose. The plastic lines leaked at several of the compression fittings when under pressure.
 
Back in the last decade when I was building, there was a rash of brake fires caused by aluminum lines that cracked at the stress loop. I don't recall if the lines in question cracked because they were over bent or because of age. Either way, I installed braided stainless steel lines from the firewall down to the brake.

A few years later I changed out the plastic lines aft of the firewall with braided stainless steel.
 
On the RV8, the plastic is only used for low presure applications such as from the resevoir to the master cylinder. Aluminum or braided high presure lines from master to slave cylinders.
 
Brake Lines

I noticed you go straight into the Brake connection with no loops.
Might want to loop the tubing around the landing gear once before it goes into the Brake. This is shown in the manual. It helps with the flex of the tubing during breaking and stops cracking of the tubing over time.
 
personally, I'm a little leery of using a solid line for this application. watching how much movement there is in the gear legs on a 4 I would be very worried about stress fractures in the line. When I replace mine I will go with braided SS line.

bob burns
RV-4 N82RB
 
FlyinTiger said:
If anyone sees anything worth commenting on or has a recommendation, experience or other thing to share, please do!
Click to expand...

Please don't take this the wrong way. I would reconsider the work you have done.

A solid aluminum line like that tied to the landing gear is asking for trouble. The landing gear on the 4 is all over the place when you taxi. Not to mention when you slow down from landing. And the wood stiffeners are not on potentially making things worst.

The aluminum bend at the interface with the caliper look like it has/had kinks. That is not good.

The line near the lower engine bolt is way too close to the bolt and mount. The combination of gear leg movement and all the vibration on the FWF will be bad news for that line. If you want to keep it, you should place some RTV or something between the parts.

The transition to the plastic line is another point of potential failure. You should consider making the transition (if you must) using a bulk head fitting.

Like I mention at the beginning, please don’t take this the wrong way. You asked for input and those are some of the things I have observed over the years.

I am not saying the way I did mine is the right way, but is an example you can look at. Picture is worth 1000 words. click here http://www.vansairforce.com/community/showpost.php?p=593078&postcount=156
 
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We're can braided stainless lines be bought I would like to change out mine at least from the fuselage to the calipers , I'm not sure my local hose making company would be able to make some small lines with fittings on them ,
 
al brake lines

This is my experience with RV-4 brake lines.

For about the first 5 years I used what was supplied in the kit... ie. the plastic lines and compression fittings..
the fittings at the brake leaked constantly and the low pressure lines from the reservoir to the cylinders leaked always in cold weather.

In the end, I used aeroquip hose from the reservoir to the cylinders, I replaced the plastic with aluminum up the gear leg with a short section of aeroquip from the brakes to the aluminum line. I retained the plastic hi pressure line from the cylinders to the gear leg. I totally expected to replace those lines eventually but after 6 or 7 years they are performing well.

Personally I don't like long runs of braided hose because it weighs so much. Its darned expensive too

Look at some certified aircraft for ideas on how to do the brake lines.

cm
 
Appreciate the feedback

Thanks to everyone who posted...I've got some reconsidering to do. Maybe a flexible solution like the braided lines would be better since the gear move so much, that seems to be a straight-forward installation without any worries about stress fractures.

Any recommendations on making tight bends in the aluminum as would be required to go all the way around the gear leg before going into the brake caliper? I used a tubing bender (grooves and wheels) and spring bender.

As far as the pins went, I was lazy and didn't want to take the wheels off. It would have been pretty simple to get them in and out with the wheels off.
 
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The plastic lines on the pressure side will always seem to seep. As well I had mine blow a pin hole in it when doing my run up just after I bought the plane with 500 hrs TT. I was lucky it happened at that point and not during landing. There have also been several reported failures of the plastic lines. I changed all of mine on the pressure side to high pressure line's made at one of our hydraulic shops. On the return side I left them the same and have been monitoring them and they have never so much as seeped anything at least of yet.

Tim
 
TS Flightlines

Sonex 541 said:
We're can braided stainless lines be bought I would like to change out mine at least from the fuselage to the calipers , I'm not sure my local hose making company would be able to make some small lines with fittings on them ,
Click to expand...

Tom at TS Flightlines made my braided brake lines for my -4. Outstanding communication, product, and service. I highly recommend him. He posts n VAF frequently.
 
Braided Steel

Well, I took the plunge and went with all braided steel lines.
Pics below:

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other stuff

Now I hear that braided lines have their own issues...

1. They have to be replaced every 5 to 7 years because the teflon lining deteriorates.

2. Noises can come from the lines, squeaking or howling...not sure from which part.

3. They are heavier...to the tune of 2 pounds.

4. More expensive. They do look nice, but it comes at a price.

Any other "issues" I should be watching for? I'm learning as I go and have learned a lot already.
 
FlyinTiger said:
Now I hear that braided lines have their own issues...


Any other "issues" I should be watching for? I'm learning as I go and have learned a lot already.
Click to expand...

Where you have them in direct contact with the gear leg, they will abrade the gear leg. There is still quite a bit of relative motion here. Chances are it would just rub through the paint but then you have rust issues on your gear.
Even aluminum tubing will rub through and it is much less abrasive than stainless sheathing.
 
JonJay said:
Where you have them in direct contact with the gear leg, they will abrade the gear leg. There is still quite a bit of relative motion here. Chances are it would just rub through the paint but then you have rust issues on your gear.
Even aluminum tubing will rub through and it is much less abrasive than stainless sheathing.
Click to expand...

The option that fixes this problem is to buy the Teflon braided hose with an integral outer layer of vinyl...
 
My Cessna 180 has solid aluminum brake lines for the landing gear legs. They are 1/4" diameter. There are no loops. Since the 180 has a softer landing gear than the RVs I've flown, I'd expect more flexing of the line for the Cessna; the brake itself has at least as much local movement.

The brake lines are original from 1955 and are fine. The airplane has 3,600 or 3,700 hours, including rough fields and off-airport operations and probably worse, my landings. The brake lines are fine.

I plan to build the lines for my RV-3B just the same.

No flex hoses needed for this, but I will use flex lines from the reservoir to the cylinders and the cylinders to the firewall.

Dave
RV-3B building
Cessna 180 flying
 
David Paule said:
My Cessna 180 has solid aluminum brake lines for the landing gear legs. They are 1/4" diameter. There are no loops. Since the 180 has a softer landing gear than the RVs I've flown, I'd expect more flexing of the line for the Cessna; the brake itself has at least as much local movement.

The brake lines are original from 1955 and are fine. The airplane has 3,600 or 3,700 hours, including rough fields and off-airport operations and probably worse, my landings. The brake lines are fine.

I plan to build the lines for my RV-3B just the same.

No flex hoses needed for this, but I will use flex lines from the reservoir to the cylinders and the cylinders to the firewall.

Dave
RV-3B building
Cessna 180 flying
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The Grummans are like you describe, and they do have problems with the lines at the brake cylinders -

LeftWheel.JPG


The first adel clamp up the leg is on a springy, flexible mount to help movement.

I would much prefer flex hose in this location. The Grumman flat leg can only flex in one direction, the RV circular leg can flex in multiple directions.
 
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clear vinyl coating

I am happy to say that the steel braided hoses have a clear vinyl coating that is sure to keep them from being abrasive. This is why I was comfortable putting them right up against the landing gear legs.

As far as my first attempt with the aluminum lines, I used plastic hose to protect the gear legs and aluminum from rubbing together. See pictures in earlier posts.

As far as teflon and its reaction to brake fluid over time, I'm going to have to do more research. The translucent plastic hoses I took out were original. Nothing in the log books about them being replaced. Yes, over 20 years old and were still working though leaking here and there.
 
FlyinTiger said:
As far as teflon and its reaction to brake fluid over time, I'm going to have to do more research. ....
Click to expand...

Check page 18 of this FAA document -

https://www.faa.gov/regulations_pol...craft/amt_handbook/media/FAA-8083-30_Ch07.pdf

"...It is compatible with nearly every
substance or agent used. It offers little resistance to
flow; sticky, viscous materials will not adhere to it. It
has less volumetric expansion than rubber, and the shelf
and service life is practically limitless. Teflon? hose
is flexible and designed to meet the requirements of
higher operating temperatures and pressures in present
aircraft systems. Generally, it may be used in the same
manner as rubber hose. Teflon? hose is processed and
extruded into tube shape to a desired size. It is covered
with stainless steel wire, which is braided over the
tube for strength and protection. Teflon? hose is unaffected
by any known fuel, petroleum, or synthetic base
oils, alcohol, coolants, or solvents commonly used in
aircraft....
 
excellent

Mr. az_gila,
Thank you for a reference document. Being new to the "nitty-gritty" of aircraft maintenance it is good to have references.
Side note...the original plastic lines supplied by Vans were in the -4 for 20 years. I wonder what the advertised lifespan of those lines is?

Great news, the brakes are more solid than they've ever been, I feel very "in control" of my wheel braking and have piece of mind that the lines are going to last a while.

Thanks to everyone with advice.

Al
 
No squeal

So far no squealing brakes. I've got silent brakes and the pedals are staying very firm. Must have been some flex in the side walls of those plastic lines.
 
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