bleeding brakes

[Yetti]

22 minutes ago, RobertGary1 said:

I’ve done that but it depends on how clear the lines are. If you have old fluid in there you want more pressure to push it through as it’s a bit gelatinous. 

-Robert 

That why you use vacuum to suck all the yucky fluid out first.

[Jerry Pressley]

didnt work      

[kortopates]

22 hours ago, acpartswhse said:

didnt work      

What didn't work?

[Jerry Pressley]

my last post on flying and pumping didnt work

[kortopates]

I have dual brakes and must of spent 40+ hours bleeding before I found what finally works for me. I disconnect all master cylinders from their mounted positions - but not the hoses. Then with ATS brake pressurized bleeder with several quarts of fluid I open the flow to push a quart of fluid up from the caliper through the reservoir and out to catcher bottle.  With the fluid running I start with the copilot master cylinder and rotate it so the hose connections are the high spot (rather than off to the side) and I tap it with the handle of big screw driver to knock air bubbles free. I can readily see the air bubbles move through the reservoir nylo-flo line from pilot brakes to the rear reservoir. After I can't get any more air bubbles out of the co-pilot master cylinder I move up to the pilot master cylinders again rotating the MC in hand to move the hose outlets to the top and tap while I pushing fluid through. I then put the MC back into position and pump the brakes x10 on each. Then again back underneath with MC free hanging from their hoses and I keep repeating this process till I can't get any more air bubbles out. I'll even wait over night and test one more time with my feet before I button it back up.

But until I started rotating the unmounted MC's and tapping them while pushing fluid through them under pressure I put countless quarts of fluid through without getting the stuck air bubbles out. 

Edited August 5, 2019 by kortopates

[PT20J]

Anyone ever thought to ask Mooney how they do it at the factory? There must be some trick (or is the labor involved the reason new ones are so expensive?)

[kortopates]

33 minutes ago, PT20J said:

Anyone ever thought to ask Mooney how they do it at the factory? There must be some trick (or is the labor involved the reason new ones are so expensive?)

Somebody posted what Stacy recommended either above in this thread or in Chris Marauders thread - I don't recall it was any different than the standard aircraft method.

[PT20J]

10 minutes ago, kortopates said:

Somebody posted what Stacy recommended either above in this thread or in Chris Marauders thread - I don't recall it was any different than the standard aircraft method.

Well Ellis should know. Maybe it’s better to let it all drain out and just start over. Good to replace the fluid every 5 years or so anyway. Mine was heat discolored for about 8 oz worth at the calipers even though it was changed 2 years ago by DMax. 

Skip

[kortopates]

4 minutes ago, PT20J said:

Well Ellis should know. Maybe it’s better to let it all drain out and just start over. Good to replace the fluid every 5 years or so anyway. Mine was heat discolored for about 8 oz worth at the calipers even though it was changed 2 years ago by DMax. 

Skip

I drained mine empty as well, but I was also replacing all my hoses and all new MC's and calipers as part of dual puck brake upgrade. By starting clean, I was okay recycling the brake fluid back through after an initial flush so to speak -- or I would have gone through gallons of brake fluid!

[flyer338]

Once upon a time I was a certified Master Automotive Technician. I modified and maintained a M20C (under appropriate supervision) for more than ten years. I found a foolproof way to bleed brakes that works on motor vehicles and airplanes. It is very simple: ensure the fluid reservoir is full, open one bleeder screw, and go have a cold beverage. Return, close the bleeder, top off the reservoir and then open the bleeder screw on the other side. Have another cold beverage. Close the bleeder screw, top off the reservoir, and you are done. The pro-tip is to use a small hose to direct the waste fluid into an appropriate container and avoid making a mess on the hangar floor. 

[RobertGary1]

5 hours ago, flyer898 said:

Once upon a time I was a certified Master Automotive Technician. I modified and maintained a M20C (under appropriate supervision) for more than ten years. I found a foolproof way to bleed brakes that works on motor vehicles and airplanes. It is very simple: ensure the fluid reservoir is full, open one bleeder screw, and go have a cold beverage. Return, close the bleeder, top off the reservoir and then open the bleeder screw on the other side. Have another cold beverage. Close the bleeder screw, top off the reservoir, and you are done. The pro-tip is to use a small hose to direct the waste fluid into an appropriate container and avoid making a mess on the hangar floor. 

The problem with airplanes is that the bleeder is on the bottom of the caliper which is why it requires pressure to not have an air pocket in the top of the caliper. 

-Robert 

[flyer338]

Try it. It works. 

[RobertGary1]

After replacing my brake flex hoses in the wing and many gallons of fluid pressured up the system my brakes were soft or almost nill in the AM. After pumping the brakes during some full rudder slipping back and forth they seem fine now.

-Robert

[FlyingDude]

Hey guys,

We're planning on replacing the flex hoses in the wings and doing the caliper speed mod this weekend. I've read the threads and have a few questions:

- what's the total capacity of the brake system? I have pilot side brakes only. I mean how much fluid into the reservoir, entire plumbing, cylinders, calipers, etc. At this point, I'll just flush out the system and push fresh fluid in.

- what bleeder do you use? I've seen a few models at harbor freight, but couldn't decide...

- By the alternative method, How do you connect oil drippers to the calipers? 

- are there any gaskets that go between the under-wing flex hoses and calipers/fuselage metal pipes? 

- I don't need to bleed the flap system just because the brake system got worked on, right?

If the bottom location of the caliper vent is such a problem, I'm going to bleed the system "before" competing the speed mod, in that I'll zip tie it to the gear truss with the bleed nipple facing up...

Thanks for your help.

Cheers

[A64Pilot]

I don’t think you’ll get a knowledgeable answer on total capacity, but I’d bet lunch it’s way under a quart. Still have two on hand and buy that silly insect sprayer that’s way overpriced at AC Spruce to make life easier. I’d disconnect the reservoir can and use a Ball Mason jar or similar, holds a lot and you can see when it’s getting full, never hurts to flush a lot of clean fluid through.

‘Sometimes though a pedal that just goes away isn’t air, it’s the O-ring or rings in the Master cylinder, especially if it comes and goes, air doesn’t usually come and go, it stays 

[FlyingDude]

3 minutes ago, A64Pilot said:

silly insect sprayer that’s way overpriced at AC Spruce

This?

I've got 2! One for washing the engine one killing weeds in the yard. Don't need a 3rd one

[A64Pilot]

Yes that one. After you have it awhile it will get sticky too from the 5606 softening it. It is overpriced, but is worth having.

[FlyingDude]

8 hours ago, A64Pilot said:

Yes that one. After you have it awhile it will get sticky too from the 5606 softening it. It is overpriced, but is worth having.

I just built my own from a new $6 squirter I got from harbor freight

[A64Pilot]

13 hours ago, FlyingDude said:

I just built my own from a new $6 squirter I got from harbor freight

It’s the fittings that are useful, and the 56506 will eat up the rubber in a regular insect sprayer, so buy another $6 one for when the first one won’t pump up or hold air anymore.

[Guest]

A 10$ pump oil can with a length of pitot-static line has worked for more than 30 years.

Clarence

[FlyingDude]

25 minutes ago, M20Doc said:

A 10$ pump oil can with a length of pitot-static line has worked for more than 30 years.

Clarence

Yep, other Mooniacs suggested the same the same thing, so I got 15' of 1/8" hose (it's cheap, so why not) and hose clamps from Napa to ensure tight fit and I'll give the oil can method a shot first. 

Another mechanic suggested that I cap the fitting on the rigid line to prevent draining the system and filling up and bleeding the new hose and then joining them. He says that with this method, he can bleed the system by pumping on the brakes a few times. I'll use this opportunity to actually flush the system, so I'll overfill the reservoir and wait until good oil comes before capping the rigid line fittings... Anyway, I got an assorted set of vacuum plugs from Napa for this purpose, as well.

Thank you all for all your help

[A64Pilot]

You may find that .020 safety wire will hold the vinyl plastic line on the bleeder valve better than a hose clamp.

‘I prefer the pressurized bottle as you can open the bleeder valve slightly and have a steady slow flow thorough the system, it makes it easier for a one man operation.

[Fly Boomer]

On 7/24/2019 at 7:48 AM, Shadrach said:

Once a vac is attached, draw system down to ~ -18 to 20inHg and have someone actuate the brakes and parking break for a minute or so. This should eliminate any stubborn air bubbles from the system. 

Any idea if this would work using one of the compressed air and venturi vacuum sources?

[jetdriven]

On 8/4/2019 at 7:36 PM, kortopates said:

I have dual brakes and must of spent 40+ hours bleeding before I found what finally works for me. I disconnect all master cylinders from their mounted positions - but not the hoses. Then with ATS brake pressurized bleeder with several quarts of fluid I open the flow to push a quart of fluid up from the caliper through the reservoir and out to catcher bottle.  With the fluid running I start with the copilot master cylinder and rotate it so the hose connections are the high spot (rather than off to the side) and I tap it with the handle of big screw driver to knock air bubbles free. I can readily see the air bubbles move through the reservoir nylo-flo line from pilot brakes to the rear reservoir. After I can't get any more air bubbles out of the co-pilot master cylinder I move up to the pilot master cylinders again rotating the MC in hand to move the hose outlets to the top and tap while I pushing fluid through. I then put the MC back into position and pump the brakes x10 on each. Then again back underneath with MC free hanging from their hoses and I keep repeating this process till I can't get any more air bubbles out. I'll even wait over night and test one more time with my feet before I button it back up.

But until I started rotating the unmounted MC's and tapping them while pushing fluid through them under pressure I put countless quarts of fluid through without getting the stuck air bubbles out. 

That’s great info.  The older J models have hard aluminum tubing and your technique is not possible. I spent dozens of hours trying  to bleed mine with this setup, they’re just ok 

[kortopates]

26 minutes ago, jetdriven said:

That’s great info.  The older J models have hard aluminum tubing and your technique is not possible. I spent dozens of hours trying  to bleed mine with this setup, they’re just ok 

At least try disconnecting and rotating the MC and the tapping to get any trapped air out even though you can't see the air bubbles. I was amazed at how much trapped air there was and I assume its because the MC hose connectors are not at the high spot on the MCs. But I bet you'll see noticeable improvement right away.