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Brake bleeding frustrations (long)

Jeff R

Jeff R

Well Known Member
Bleeding these brakes is starting to rank right up there with one of the most frustrating things I have had to do. I have never bled brakes before but didn?t expect too many problems. How na?ve I was! I decided to go with DOT 5 fluid, as that was available locally, and a friend lent me a hand operated vacuum pump he uses to bleed brakes on his Harley. I had read of the oilcan pumping method, but I really don?t see why one would get more bubbles using a vacuum vs. pressure, plus I didn?t want to have to make an oilcan pump and this vacuum pump gizmo was pretty neat. So, Friday I started on the left side and it workeds pretty good. In no time at all, I had that side done and I was really feeling happy. Then I started on the right side. I pumped until my hand was too sore to pump and I could not get the fluid past the right brake cylinder. It was getting time for the KU basketball game so I came inside and was happy after a convincing win, but this morning was such a beautiful day I decided to go out to the airport, pay my empty hanger a visit, and see what else was going on.

I ran into Chuck, my hanger neighbor who built a Glasair and I asked him about brake bleeding and he espoused the conventional wisdom that you need to pump from the bottom and he lent me this oilcan pumper and gave me a quart or so of 5606. I figured I would try it on the right side. I pumped and noticed some leaking from the AN fitting at the landing gear to fuselage connection. It was tight, but I gave it an extra tug, then I pumped some more and it still leaked. Urgh! I disconnected the fitting and discovered the flaired end had snapped. Yikes. I pulled the fitting off, dug out some new ones, re-flaired the tub and put it all back together. I re-pumped, but I could never seem to get the fluid up the tube. It seemed like there was a clog in the lines or something that stopped the flow. I verified the parking brake was not set and systematically disconnected various fittings to isolate any clog, but nothing.

As a sanity check, I moved back to the left side and tried pumping, and I had the same problem. What the? I knew there were no clogs as I have sucked fluid down the day before. But, as I pumped the can, the pressure would build up and the pump would start to leak or the nozzle fitting would come flying off. (That little bleeder value nipper is tooooo danged small.) This was what had happened on the right side, too.

I was getting pretty frustrated and running low on DOT 5. I had 2 pints and I think most of it was contained in clean-up rags that were piling up. I also started wondering about all that silicone. Would traces of silicone end up on the areas I would want to paint, and cause terrible fisheye problems? I decided to switch to the 5606. Draining out what all I could of the DOT 5, I started pumping on the right side. Man, it went right up and all the way to the reservoir. It was cool! Not having any idea why the DOT 5 wouldn?t pump up but the 5606 did, I moved back to the right side, thinking my first attempt at bleeding brakes was about to be over with a successful finish. No such luck. After a heck of a lot of effort and disconnecting fittings and reassembling them and finding nothing, it all started to pump and the fluid almost made its way to the reservoir when I noted another small leak from that AN fitting I had changed out earlier. I gave it another hard tug to tighten, but it still leaked. Dern. I dissembled the fitting and discovered I had again snapped the flair. Sheesh. And I was out of spare fittings, so I will need to order some more. I think I will also order some more aluminum brake line, as I saw that when I was tightening it, it was twisting, so I may have work-hardened it.

At least some of the frustrations were reduced for a bit as I got to see the last half of the KU-Missouri football game, where we pulled out a win, but it went down to the final few seconds, literally, before it was really over. Amazing game.

Anyway, I guess tomorrow I will work on something else, but this brake bleeding has sure been a pain. I would encourage others to bleed the brakes as early in the build process as they can. I can?t image the frustration if I had my instrument panel ribs and all riveted in.
 
Thanks for writing this Jeff. I am about to bleed my brakes too. I have only left side set with individual reservoirs. What do you think was the problem of snapped flare? Did you overtighten?
 
Bleeding..

In a perfect world pressure or vacuum should work to bleed brakes. In my experience however only pressure (oil can) really works. The vacuum system will find any leaks and allow air in to frustrate you. As to the inability to get the fluid from the bottom (caliper) to the top (reservoir) the usual catch is the master cylinder. The cylinder will only allow the fluid to flow through if the piston is in the fully retracted (brakes off) position. If the port in the cylinder is covered, as it would be at the beginning of brake application, the fluid will not flow. This condition will also cause dragging brakes.

John Clark
RV8 N18U "Sunshine"
KSBA
 
Mixing Fluids

If you have mixed 5606 with DOT 5 you now have glue in your system. As described by an A&P: "...but you never want to mix 5606 and DOT 5. You will end up with a gel that will be **** to flush out."
And yes, you can imagine how I know that! Try it on the bench. I flushed 5606 out with Dot 5 and made a complete mess. Had to flush everything with alcohol for hours and rebuild my brakes and cylinders cleaning the resulting goo of everything. The only problem I had that you probably don't is the 5606 ate the o-rings in my master cylinders as they were not aircraft parts. Now all is clean and using DOT 5 with no problems but it was a very long weekend. :rolleyes:
And yes, getting it on areas that will be painted later will be an issue!
 
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When you go to bleed the brakes, make sure that you pull back on the top of the pedal to ensure that the master cyl is in full release (open). There is only .080" between open and closed.
 
What Gasman said.....

When you go to bleed the brakes, make sure that you pull back on the top of the pedal to ensure that the master cyl is in full release (open). There is only .080" between open and closed.
Click to expand...

I'll second that....I went through the same frustration a couple months ago. Spent probably 4 or 5 hours over two days trying to fill with pressure from the bottom. Then after sitting on the hangar floor for about 15 minutes thinking about what I could be doing wrong (after all, the advice I'd read on VAF made it sound so simple!!), I thought about the fact that I had not added return springs as some have done at top of the master cylinders to help ensure the pedals fully rebound. For lack of other ideas, I climbed into the cockpit, pulled forward on the tops of all four pedals (got some slight movement, but not much), then crawled back under the plane to try again. Was done with both sides less than 5 minutes later....

A couple weeks later, I helped a guy a few hangars down who was having trouble doing same thing. Same solution made it a 10 minute job when I showed him how I did mine.

I used a $7 small garden sprayer from Lowe's Hardware to send fluid under pressure up through the bleed screw. Had a tube fitting screwed into the reservoir with a return tube connected from there down to a collector container under the plane with me. That allowed me to do this by myself with little to no leakage once I figured out I needed to pull the pedals back (I did go to the hardware store shortly after that and bought some compression springs that I added external to the master cylinder rod to assist in pedal return).
 
Jeff R said:
Urgh! I disconnected the fitting and discovered the flaired end had snapped. Yikes. I pulled the fitting off, dug out some new ones, re-flaired the tub and put it all back together.


I noted another small leak from that AN fitting I had changed out earlier. I gave it another hard tug to tighten, but it still leaked. Dern. I dissembled the fitting and discovered I had again snapped the flair. Sheesh. And I was out of spare fittings, so I will need to order some more.
Click to expand...


Are you using a torque wrench? if not i would highly reccomend it. you really shouldnt be breaking fittings. when a fitting leaks, tightening it almost always makes it leak worse. typically the flare on the line has cracked and the tightening will finish it off. YMMV.

good luck with your bleeding. i get to do mine this week.:( thanks for the heads up on the pedal travel. I guess i should put on the srpings i have laying on my bench.:eek:
 
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Thanks for the suggestions, including a few PMs I received.

I do feel a bit stupid over some things, but I am happy that some good points have been raised that will help others out.

It does seem that of all the AN fittings, I only had trouble with this one. I suspect the connection failed the second time as the aluminum tubing was work hardened by the twisting that occurred when I kept tightening it after several assembly/disassembly sessions. That, and over-tightening in an attempt to stop the leak, led to the shear failure of the flair.

I hadn't even thought about DOT 5 and 5606 turning into a glue. I figured I would just force out the DOT 5 and all would be fine. I will run an experiment to see if it does, in fact, form a glue or gel. If it does.....ugh.

I did note some problems getting fluid up through the actual brake assembly. Not sure why. I disassembled one side and that seemed to clear up a problem. I had been pumping the rudder pedals so I don't think that was the problem. Maybe it was but I was not aware of it. I only wrote down a fraction of the things I was doing.

Do they make longer bleeder valves? Having less than a 1/4" to slip on the filler tube just doesn't work well.

But thanks for the suggestions! I'll report back when I finally lick this thing.
 
MIL-83282 vs. MIL-5606

Just a word here about MIL-83282 replacing 5606. Most of the airlines and the military have converted to the "5-digit" hydraulic fluid because it is much less flammable. There have been many brake fires in plastic, nose-wheel airplanes resulting in the aircraft's total destruction. I think that it would be a good idea for all nose-wheel aircraft at a minimum to convert to 83282, also known as Aeroshell 31. The good thing about this conversion is it does not require a change in seals, as a matter of fact, the two fluids are interchangeable, so no flushing is required prior to converting. Just drain the old fluid and bleed with the new. A gallon sells for about $15, probably less than 5606. The new fluid is synthetic but non corrosive (like Skydrol is). But, please, do your own research!
 
Jeff - I'm sorry you had to go through this. This is the kind of thing that usually happens to me! ;)

I'm sure you saw my post in the tips section about the oil can pump contraption. It's a bit rube goldburg - but boy did it work so easily. I did both sides of the Skipper in about 20 minutes total and they are rock hard. The plane has a brake design that is identical to a dual brake RV - the parts even look similar. It has a parking brake valve too - be sure it is open when you are bleeding.

The only thing that was a bit tricky was that I had someone inside tapping / moving the brake pedals. This was to remove stuck air and also to be sure the master cylinder is open. I had that person (my daughter) tap/move first the brake "closest" to the calipers and then the one closest to the reservoir. From your description it sounds like something was closed in the system while you were trying to bleed - either the parking brake or master cylinder. What I liked about the oil can was that you could "feel" the fluid moving through the system as you pumped it up from the bottom.

Good luck - you'll get it.

BTW - I agree with the poster above - I'll be using the "5 digit" MIL fluid in my RV. The Skipper will be fine with old school 5606 - it lands pretty slow and has big, open brakes.
 
I had issues yesterday

I was stuggling with mine for a while yesterday as well but I had different issues.

I'm using the oil can up from the bottom. I want to make sure that I don't have any leaks before I rivet on the skin above the instrument panel. A week earlier, I put the majority of the fluid into the system but I wanted to get all the air out yesterday.

My issue was getting air bubbles to go past the wheel cylinders. This happened on both sides. I could see a bubble in the lines then, when pumping fluid into the system, I could see it move into the cylinder but not out and then into the resevoir. Now I did see air bubbles moving from the cylinder to the resevoir early in my attempts but there were a few stubborn bubbles that would go in, but not past, the cylinders later in the process. The funny thing is that I was able to pump fluid out of the resevoir and into a cup but the air subbornly remained within the cylinders, only to be sucked back into the lines during a check of the brakes. I finally put a bowl under the brake pedals, broke the fittings on the pedals, and pumped fluid into the system until fluid dripped out. That pretty much eliminated the large bubbles.

I say "pretty much" because I still have a couple of very small bubbles that I can see in the lines. However, the brakes feel pretty solid at this point. I wonder at this point whether a few small bubbles are acceptable as long as the brakes feel good. Is the fact that, unlike in a car, I can now see air bubbles in the plastic lines causing me to think there is an issue when there isn't one? I've bled brakes in cars many many times and the indication that you are done is when you have fluid running out of the bleeders and that the brakes feel good. For all I know there still is air in the lines in my cars but it's insignificant.

By the way, for fluid I used Mobile 1 Synthetic ATF. After doing some research on this list, it looks like it has been sucessfully used for years. It has very similar properites to the 5 digit mil spec fluid but is a lot easier to get for me and I can buy it in quarts, not gallons!

Any thoughts?
 
I used 5606 and pumped from the bottom with an oil can thingy, no problems. I have clear lines from Vans and found after a couple days that a bunch of air was in the lines. I removed the lines at the nearest fitting and thought, I'll just put the line up and let the air come out and refill the line with my trusty oil can, but wait, the fluid would not settle in the line, in fact to get the air out I had to tap on the line to do so. I fought with this for a few minutes and than got an idea, just let the hose down and let the fluid drain out, yup, the air came right out, reinstalled the hose and all done.

I don't know what you guys do for seeing this kind of air in the system with the bonaco lines, but to each their own.

I think this 5606 fluid is heavy and thicker than regular brake fluid, so the thoughts of what this stuff does with air in it is confused. I work with brake fluid in cars all the time and I know that bubbles go up with this stuff. But with the 5606 it doesn't like to do this. So I think if you have air in the lines, try letting it gravity out by opening up a fitting below the air. Also make sure the reservour is always full before tring this.

I also heard that the brakes on the A models are a little on the weak side and that too much use will cause them to fade, get hot. So I went to the Grove set up, which is suppose to give you I believe, twice the kenetic stopping over stock. I also asked Robbie what fluid to use, he said only 5606. THis was a couple months ago.
 
Bleed Screw

Had a bit trouble bleeding the brakes on the 9A. Couldn't seem to get all the bubbles out.
Machined this screw to thread into the wheel cylinder. I've always found that trying to pump fluid in through an open bleed screw can induce air into the system that gets past the threads.

By USCANAM
Still had a few bubbles in the system before starting to fly, but now they are all gone.
Maybe it's the changes in air pressure!!

Jack
 
Jack, that looks like just like we novice brake bleeders need! You wouldn't want to sell or rent it out would you?
Jeff
 
A tool just waiting to be designed

I used the oil pump can when I first did my brakes and made a complete mess. The problem was transitioning from a big hose that fits on the end of a can to a little hose that fits on the nipple. Most recently when I replaced my brakes, I used a garden sprayer pump. It seemed to work OK once but then had trouble.

Someone out there could do very well for themselves if they could come up with a 'kit' or some sort of self-contained solution that worked well, didn't leak all over the place!!
 
The new fluid is synthetic but non corrosive (like Skydrol is).
Click to expand...

Skydrol is the best paint remover there is. Skydrol is NOT as harmless as the labels indicate. It is corrosive and DANGEROUS.
 
Well, the DOT 5 doesn't remove paint as I dripped more than a few drops on my painted cockpit flooring (Rustolium Painters Touch, whose durabilty I have been very impressed with).

I also mixed a little DOT 5 and 5606 together and didn't notice any issue with it turning into a gel or anything.

I am noticing some minor tingling of the skin of my fingers where both fluids made contact yesterday. Well, they made a lot of contact. I will be a little more careful with the gloves next time.
 
Jiggle the Pedals Even With the Springs

I just bled mine today, and I had to jiggle the pedals a bit to get the flow going on one side.

Hans
 
Another Option

In the past, I struggled with the same problems until I switched my technique. Now I can bleed the brakes easily with excellent results. I went out on EBAY and found a brake bleeder kit for about $60. It is kind of hard to describes but it has a plastic quart bottle with a metal valve and hoses with a pump bulb attached. Here's how I do it.

First, I pump from the top down, not the bottom up. Second, I create a closed system so no air can enter. I attach the line with the pump bulb to the brake reservoir. I attach the return line to the bleeder fitting on the brake cylinder with a twist of safety wire. The other end of this tube goes into the top of the quart bottle of the bleeder with the end down below the level of fluid in the container. I open the bleeder valve and open the valve on the bleeder and pump fluid through the system with the bulb until there's no air bubbles coming out of the end of the tube that's stuck down in the fluid. Now I pump the brakes in the aircraft to make sure any remaining air in the tops (bottom) of the master cylinder is forced out. Squeeze the bulb a little more until I'm sure there's no air and that's it. Before I do anything, I close the bleeder valve with the hose still attached. Now I can disassemble the hoses, drain them back into the fluid can, and clean up any remaining drips.

BTW, I use Mobil-1 synthetic ATF fluid exclusively.
 
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One of the A&Ps here at Flagstaff made up a brake bleeding outfit that worked well for me. It's basically a pressure bottle with a fitting for an air compressor and an output line with a fitting for the brake bleed valve. With about 40psi pressure in the bottle and hooked up to the brake, cracking the valve on the output line sends fluid quickly through the system. With someone inside the cockpit, we could see any bubbles in the plastic lines and could also tell when the fluid reached the reservoir. I got lucky and had no problem with the cylinder inlets being blocked but I did find a couple of leaks and had to repeat the process after fixing them. About a half a day for the whole process. The only thing I didn't like was not being easily able to see the level in the Van's reservoir; I ended up making a little dip-stick.
 
It's just not clear!!!

f1rocket said:
In the past, I struggled with the same problems until I switched my technique. Now I can bleed the brakes easily with excellent results. I went out on EBAY and found a brake bleeder kit for about $60. It is kind of hard to describes but it has a plastic quart bottle with a metal valve and hoses with a pump bulb attached. Here's how I do it.

First, I pump from the top down, not the bottom up. Second, I create a closed system so no air can enter. I attach the line with the pump bulb to the master cylinder. I attach the return line to the bleeder fitting on the brake cylinder with a twist of safety wire. The other end of this tube goes into the top of the quart bottle of the bleeder with the end down below the level of fluid in the container. I open the bleeder valve and open the valve on the bleeder and pump fluid through the system with the bulb until there's no air bubbles coming out of the end of the tube that's stuck down in the fluid. Now I pump the brakes in the aircraft to make sure any remaining air in the tops (bottom) of the master cylinder is forced out. Squeeze the bulb a little more until I'm sure there's no air and that's it. Before I do anything, I close the bleeder valve with the hose still attached. Now I can disassemble the hoses, drain them back into the fluid can, and clean up any remaining drips.

BTW, I use Mobil-1 synthetic ATF fluid exclusively.
Click to expand...

If you are connecting to the master cyl, then you need to do this twice. And then have to deal with connecting and bleeding the supply lines. Or are you connecting to the one reservoir that Van's sends with his kit??

With my Piper warrior, I just connected a clear line to the wheel cyl, ran it up to the reservoir held in place with tape so I could see the line from the cockpit and just sat in the plane and pumped the parking brake till the line was clear, meaning no air. Then switched to the other side and did the same. Done in less than 10 minutes.

The Piper used a master cylinder for the parking brake. So will my RV.
 
Sorry, my reservoirs were attached to my brake cylinders. It should be, as you point out, connected to the brake reservoir.
 
problem never goes away

I have been bleeding the brakes for several months. No visible bubbles last time I looks (6 weeks ago) now there a 3" long bubbles. No dripping fluid anywhere so where is the air coming from. All bubbles are between pilot and co-pilot brakes. Seriously thinking of removing co-pilot brakes.
 
Bleeding Brakes

I also have had problems with bleeding brakes. Re: Getting the air out. A few months ago i noticed a few drops of brake fluid on the floor. On further inspection, i noticed some fluid pooling on top of the clylinder which was running down. I decided to remove the cylinder and found that the piston was scored along one side where it exited from the cylinder. Decided to replace the brake cylinder with a new one. Bled the brakes again, still could not get the air out (3" of air between the pilot & co-pilot brakes) I decided to remove the pilots right brake cylinder. On inspection, i noticed the same scoring as on the left brake. Replaced this cylinder with a new one. Bled the brakes and was able to get all the air out. I think that this scoring was allowing air to enter the system via the o-ring. Am confiring with Matco on this issue. They say to inspect the body for any witness marks of contact that is restricting the rotation of the unit. It must be free to pivit between the ends. i inspected this, and it was free. Matco says the wear is evidence of side loading on the shaft. If the unit is restricted in rotation, then the shaft can be loaded against the end gland. Just wondering if anyone has had the same problem. Will figure out how to send pics.

Newbie to the forum.
Flying a RV-6A
Building a RV7
 
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