Air in Brake lines

13 posts in this topic

Posted

Guys,

 

I keep bleeding the brakes and get all the air out of the system but as soon as I start to taxi I can see air in the line again and the brake goes soft. This only happens on the right brake, the left one is fine.  Does this meant it has a leak somewhere?  What's the best way to find it?  no brake fluid ever leaks out.  This is an old Matco set of brakes.

 

Thanks,

 

EG

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Posted

Are you pumping the fluid in from the caliper or are you pumping from the master and bleeding at the caliper?

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Posted

Get a small hand pump oil can. Fit a 1/8 clear line to it and the bleeder down below at the caliper. Open bleed screw at the master(pedal). Pump the fluid up from the bottom to the master cylinder. Type F auto trans fluid has been used if you don't have aviation hydraulic. J 13 I think. Never use brake fluid.

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Posted

Pumping up from the caliper with the red fluid from a.c. spruce. I can get the air out of the lines (nyloflow) but it comes back after I apply the brakes a time or two. All I can figure is that it is sucking air in somewhere.  Suggestions on how to isolate the leak?

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Posted

Do you have the old style master with in reservoir or a separate resi?

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Posted

make sure the bleed screw is the highest point in the cylinder or air will stay above it

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Posted

Hello all

I have the same problem as the OP (air coming again in brake lines after bleeding the brakes)

I have the "old style" Matco brakes, and it seems to me that this is caused by a leak in the right caliper.

Is there a place where the gasket and O-rings are available on mail order? I dont know if they are the same reference as in the new calipers (as seen on aircraft Spruce or on the Matco website.)

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Posted

A failed calliper seal would generally show as a weep. As for air entering,I would say possible but unlikely.The calliper "o"rings we use are nothing special and can be located at a hydraulic seal supplier.Automotive brakes usually use a square profile seal which is to retract the piston fractionally when the pressure is released,there is no advantage in this design for our use.The most common area for air to enter the system is the ring that seals the spear of the brake master cylinders.This seal rarely leaks,but will readily let air in on a sudden release of foot pressure on the pedals,A lot of dirt enters here off footware and surprisingly the passenger side on a dual setup is usually the culprit.I hope this long winded explanation is of some help.

cheers

Dusty

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Posted

In fact I modified the brake system by using a single master cylinder with a hand lever at the center. I did that because I had a lot of trouble controlling the plane on the ground while braking. I feel much   safer that way

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Posted

try tapping on the master cylinder with a screw driver while bleeding them. Air can get trapped in there then come out with vibration. I bleed mine from the bottom up then did a few pumps and cracked the screws on the calipers and couldn't believe how much air came out the bottom too.

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Posted (edited)

Bleeding Bloody Brakes...

So I'm tipping the plane forward so the feed line to the brake calipers is the highest point of the caliper. I push brake fluid in/up through the bleed niple in the caliper with a big syringe. I have the Matco MC-4 brake cylinders mounted vertically with the push rod up. 

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I can see the air, then the air bubbles go through the brake lines and then just the red fluid. Probably pushing 3 times the required volume through the system. No more bubbles.
... and the brakes are still "mushy". This is the first time I'm using the MC-4 cyliners, is there a secret way to bleed those? I don't think it is a problem with the calipers as I never had this issue before and have bled them successfully several times.  

 

Edited by FredStork

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Posted (edited)

grab the foot pedal by hand, then pump them up a few times. While holding them on crack the bottom bleed screws open and force some fluid out that way too. I had alot of air stuck in the brake calipers that came out that way. My calipers also have 2 bleed screws on them.  I did that about 5 times on each screw rock hard brakes after that.  Also clean the disk good.  Good luck to ya.

Edited by TJay

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Posted

Hey Fred. FWIW, I used to have to tip my plane side-to-side to get stubborn bubbles out.

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