bleeding brakes

[jetdriven]

So, quick update, we installed a dual brake kit, Cleveland master cylinders both sides, new Cleveland brake linings and new hoses throughout. After pushing 4 gallons of fluid through the system...

Spongy brakes that go to the floor. This after running as much as 100 PSI through it with a pressure pot. Any further ideas? This goes wh beyond bleeding a 172.

[Cruiser]

figure out where the air is trapped.

[OR75]

Byron

i had to bleed my brakes recently. the pressure pot option really did not work as air stayed trapped in there.

i just got a large plastic syringe from Tap Plastic and a few vinyl hoses of the right diameter from home depot. A foot suffice.

take out the brake fluid reservoir from the wall above the battery. remove the fitting at the bottom of the reservoir and adapt a hose to a large glass jar so you can see the bubbles coming out. fill the glass jar with some brake fluid and make sure the hose end is in the fluid ( so that if the system breathes back fluid, it will be 5606 rather than air)

inject fluid from the brake pads (very slowly but firmly) . make sure the small hose on the syringe is full of fluid as you fit it where you will inject the fluid at the brake pads valve. open the valve once the hose-syringe is one a few turns. close the valve once the syringe is almost empty. .

once in a while actuate the brake pedals.

do it as many times as you need till you don't see bubbles coming out in the jar.

once happy no more bubbles are coming out, reconnect the tubing to the brake fluid reservoir ( without introducing air)

i don't think high pressure pot helps. if air is trapped , it will compress while you apply pressure , ... then decompress and it is still there.

slow filing while disturbing the air trapped is the key.

it is a messy. it is easier to have someone help ( actuate the pedals , monitor the glass jar ) but it works.

[MARZ]

Check to make sure the calipers are traveling with brake application ??

[Yetti]

The easyist thing I have found is the small hand vacuum pumps. (mity mite I think)   Connect at the bleed screw and open.   Good for priming the system with fluid.  Then use a oil can to pump from the calipers.   Usually about 20 pumps.  May need to go up to 40 pumps.   Helps to have someone watch bubbles come through the reservoir.

 

Edited November 13, 2018 by Yetti

[bumper]

Recently bled the brakes on my Mooney, after many years of ignoring this, the brakes were getting a little spongy and "not responding" well. 

 

5606 Mil Spec fluid, given enough time, will turn into a thick, sticky, gum like fluid. This goober will most likely be located in the lower extremities of the brake system, calipers and lines, so you really don't want to initially use pressure to force this junk back into the master cylinders. So I first used the old "open the bleeder valve while helper pushes on brake pedal" method. Then while pedal is depressed, close bleeder and repeat - - just don't have the helper push pedal all the way to the bottom stop if possible, as it may get stuck fully down and require reaching in and manually pulling back. 

 

After doing the above until the tar like fluid stops coming out the bleeder, and making sure to keep the reservoir from going empty, then use a pressure pot to bleed the brakes normally from the bottom up, while moving the brake pedals some. I used a modified small garden sprayer for this. At the brake reservoir I screw in a 1/8" NPT nipple with clear line into a clear container to watch for bubbles - - that way there's no need to remove the reservoir or use an adapter on the line.

 

bumper

[DonMuncy]

Sorry Bumper. I hit the "unlike" rather than the "like" button.

[Alan Fox]

So, quick update, we installed a dual brake kit, Cleveland master cylinders both sides, new Cleveland brake linings and new hoses throughout. After pushing 4 gallons of fluid through the system...

Spongy brakes that go to the floor. This after running as much as 100 PSI through it with a pressure pot. Any further ideas? This goes wh beyond bleeding a 172.

If you didn't put the shuttle valves in the lines at the rear of the wing where the 4 master cylinder lines come together it will never bleed... EVER.....The shuttle valves look like T fittings on steroids....also , The masters bleed independent of each other , the pilot and copilot sides do not connect unless both side pedals are being pressed...

[N601RX]

I did not put shuttle valves in mine and had no trouble getting them to bleed. 

[jetdriven]

There are no shuttle valves in ours either. Early J's, before S/N 760 or so, have the master cylinders plumbed in series.

[acrotex]

Here is a "trick" I came up with today on getting the air out of the brake caliper.

In my case, I had plane up on jacks, and had the wheel removed.  Installed new brake pads and decided to put new O-ring on the piston.

First advice is to try to plug the line when you remove it to prevent the fluid from draining out.

If you do that, then all you have is air in the caliper after replacing the piston.

The "trick" I came up with was to re-attach the brake line, then open the bleed valve at the bottom of the caliper.

Then, with the caliper still "free", there is enough hose to hold the caliper upside down, with the inlet hose at bottom and the bleeder at the top.

The fluid will gravity flow into the caliper and push the air out the top.  Will make some mess as you let it flow some fluid and air out.

Ensure the resevour has enough fluid in it. Then close the bleeder.  install the caliper and then pump the brakes. Mine were solid.

You may have to do this twice if still some air in caliper.  If you let all the fluid bleed out of the lines, then you have to go to plan B and back bleed the brakes.  Screw a fitting with small hose to top of resouvour and put the hose into a jar or can and force fluid from bottom. Normally a pump type oil can and soft small hose will work (have used that on other aircraft, but did not need to on the M20C.)

[211º]

Some more data points in case anyone is searching.

I used a 7/16 wrench to completely remove the drain plug, push the brakes and let the "fluid" (gooey-mess) drain.  After about an hour or so of draining, the goo was purged and the good fluid flowed out. I separated the plug from the bleed valve (1/4" wrench) and made sure the goo was out of the bleeder holes.

I then used about a fully filled mini-tin-can, two hoses (one inside the other to transition from the can to the bleed valve nipple) and counted pumps for each side.  After three or four counts/pumps to 25 (and resetting the bleed valve to test) the brakes came back (win!).

Here are some pictures.

[DonMuncy]

21 minutes ago, 211º said:

Some more data points in case anyone is searching.

I used a 7/16 wrench to completely remove the drain plug, push the brakes and let the "fluid" (gooey-mess) drain.  After about an hour or so of draining, the goo was purged and the good fluid flowed out. I separated the plug from the bleed valve (1/4" wrench) and made sure the goo was out of the bleeder holes.

I then used about a fully filled mini-tin-can, two hoses (one inside the other to transition from the can to the bleed valve nipple) and counted pumps for each side.  After three or four counts/pumps to 25 (and resetting the bleed valve to test) the brakes came back (win!).

Here are some pictures.

 

Is that Mooney approved hose  

Very good information. What precautions did you take to make sure no air was introduced from the reservoir.

This sounds a lot easier than back pressure purging.

[Yetti]

1 hour ago, DonMuncy said:

Is that Mooney approved hose  

Very good information. What precautions did you take to make sure no air was introduced from the reservoir.

This sounds a lot easier than back pressure purging.

Same homer dan tubing that the grumpy IA uses.  You are pushing the bubbles up to the reservoir from the calipers. The hard thing is finding an oil can.

Edited November 13, 2018 by Yetti

[carusoam]

Nice pics!

I like the hose diameter adjustment... hose-ina-hose...

We need a Mooney Lunch and brake fluid replacement day.

The LBs have their reservoir in the back near the batteries...

Best regards,

-a-