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Brake Bleed Systems

BruceMe

Well Known Member
So by far the best method I've ever done is messy but works great. You use an old oil fashioned oil can pump with positive pressure the fluid from each wheel up through its master and fill the reservoir.

I'm working in my buddies auto shop and all he had was the newer vacuum style. I imagine it's similar principled but from the top pulling up and in. I couldn't figure out where to put the vacuum.

What is the best (no bubbles) cleanest (no messy spills and drenched wrenching) method anyone here knows for bleeding aircraft brakes?

Thanks!
 
I've only done it once, really, but that was yesterday. My EAA chapter has one of the ATS bleeder setups that I used. There's a slick little coupler that clamps the thing onto the bleeder - I had a grand total of about one drop of hydraulic oil escape. Slick as heck. I think it took longer to get the wheel pants off and back on than it did to bleed both sides.

I really don't have anything to compare it to, other than a large syringe with Tygon tubing. I don't recommend that approach at all.
 
There's an inexpensive one for sale on Ebay, "One Man Brake Bleeder" I recently purchased and used it to fill my system. Very simple and effective. I'm told the man selling it is a homebuilder. If I recall it was around $13-18.
Jerry
 
I've never had much luck pushing fluid up from the bottom. You are pushing against the check valve in the master cylinders.

A simple technique I've used many times is fill the reservoir to the top, connect to a source of fluid to keep the reservoir filled, connect tubes to the bleeder valve and sink the ends in some cups of fluid (so they won't suck air), and pump the brakes until all the air bubbles are gone. This works every time as long as you create a closed system. One trip to the aviation isle at Ace Hardware will get you all the tubes and fittings to create said system. It actually takes more time to set up than to bleed.

Oh, BTW, I always use Mobil 1 synthetic ATF fluid. It's much less toxic than all the other stuff, cheap, and easy to source. It's been working for over 20 years now.
 
I don't think there is a check valve in the master is there? I only remember seeing a return port that gets opened up when the cup seal returns home? I did the weed sprayer pressure bleed from the bottom up, no mess, done in a few min,
 
I've never had much luck pushing fluid up from the bottom.

I've done both and I will tell you bottom up is far better and cleaner. And I've always done with cobbled together equipment not intended for this purpose.

Maybe watch someone do the bottom up method... there's no check valve on mine, it flows easily. The trouble with top down is that the bubbles want to rise... so going bottom up you're not fighting them they naturally rise with the rising fluid. It works really slick.

Mobil 1 synthetic ATF fluid.

Only reference I can find is transmission fluid, is that right?

Is this it?
 
Model airplane fuel pump and a bunch of silicone fuel tubing. Pump the fluid up into brake system from the bottom until the reservoir has some fluid in it. Repeat for the other side.

If any bubbles in the system exist, take the "inlet" hose out from the bottle of brake fluid and put it in the brake reservoir. Use the pump to circulate the fluid through the system until no bubbles remain.
 
+1 on the model airplane fuel pump.

http://www.ebay.com/itm/like/131930162137?lpid=82&chn=ps&ul_noapp=true

Get 'em while you can because apparently the model airplanes don't use this stuff anymore. Apparently, the sport is all going electric.

And one other thing I discovered during the last annual in which I re-bled the brakes. If you're using springs and such on the master cylinders to prevent against dragging brakes, you're doing it wrong.

I used a GoPro camera pointed at the brake lines and the GoPro app to display what I was seeing on a tablet down where I had the pump and fluid.

I could see small bubbles still being pushed out of the line after the brake reservoir was full. So just kept at it. The result was well worth it. A completely enclosed brake system which no longer required the springs, nor me reaching down to physically pull the brake pedals back every time I got out of the RV.
 
I've got a small garden pump sprayer and the fitting for the brake bleeder if you want to borrow it, I'm fairly close too.
 
I could see small bubbles still being pushed out of the line after the brake reservoir was full.
What I did was disconnect the line from under the reservoir and attach a 3' piece of tubing to extend the line outside the plane. Then I bled the system into a can until the bubbles stopped. When that was done for both sides, I re-attached the original line to the reservoir and filled it up to the normal level. It really takes two people to do this right.
 
What I did was disconnect the line from under the reservoir and attach a 3' piece of tubing to extend the line outside the plane. Then I bled the system into a can until the bubbles stopped. When that was done for both sides, I re-attached the original line to the reservoir and filled it up to the normal level. It really takes two people to do this right.
Or just replace the 1/8 inch vent cap with a 1/8 inch pipe thread to 1/8 inch tubing fitting and connected your tube there.
 
Brake bleeding/filling made easy

Model airplane fuel pump and a bunch of silicone fuel tubing. Pump the fluid up into brake system from the bottom until the reservoir has some fluid in it. Repeat for the other side.

If any bubbles in the system exist, take the "inlet" hose out from the bottle of brake fluid and put it in the brake reservoir. Use the pump to circulate the fluid through the system until no bubbles remain.

I used the "model airplane fuel pump and a silicone tubing" method it went flawless. AS the fluid went into the system it pushed all of the air out. Since this procedure is using a "sealed" system there is no chance of air getting in once the fluid is flowing.

I attached a short piece, (2ft), of tubing on the inlet side of the fuel pump. I attached a longer, (4ft), piece to the outlet side of the pump. Placed the short piece in the quart container of ATF and had it sitting on top of a short bar stool. Loosened the bleed fitting on the pilot's side and attached the long end to it. Cranked the pump. The fluid flowed bubble free through the entire system up to the reservoir. I tightened the bleed fitting with the hose still attached as soon as the fluid reached the reservoir. I then disconnected the hose and I repeated the process for the passenger side.

All of this was done with the top forward skin removed from the plane. I have yet to rivet it on to allow for access.

Oh, BTW, the mess was minimal. One drop each time I disconnected the hose from the fitting. A folded paper towel caught that drip.
 
Brake line system geometry

Brake lines that run progressively from the bleed valve at the bottom of the brake caliper , progressively up hill all the way to the top of the master cylinder are the easiest to fill with zero bubbles or mess. You just need to know the volume displacement of the entire system and use a 50 CC syringe. However Rockets and RV4's have a nasty loop of brake line that is higher than the master cylinders and this makes for the requirement to circulate a volume of fluid to purge any air that naturally migrates to the top of the brake line system loops.

There is a wide array of plumbing arrangements and master cylinders and reservoirs on the various RV's. Therefore different methods are best with a specific system.
 
Due to the viscosity of the brake fluid and the diameter of the brake lines, air bubbles will not freely float to the top.

The lines can be purged in either direction. The fluid will push bubbles down, but not easily in the wheel cylinder. The determining factor is where the bleed valve is located on the wheel cylinder. If it is on the bottom, then it is easier to push the air up and out of the wheel cylinder.

Don't stop bleeding just because fluid comes out the other end..... keep pumping till you have passed at least 6 to 8 oz. through the system without any bubbles.
 
I am going to try this, what are your thoughts? My brake fluid tank is an aluminum tube with ends welded on as supplied with the kit. The top has a vent fitting screwed into it with about a 1/8 pipe thread in it. At least that is what it looks like I have not checked it yet. My plan is to screw a barbed fittlng in the vent spot and hook a bug sprayer hose to the barb. With fluid in the sprayer it should flow into the brakes when the bleed valves are opened. I have bled cars like this with no problem. Is there any reason this will not work? Thanks in advance!
 
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