Dom Posted June 11, 2020 Report Posted June 11, 2020 I am working on a M20K. We have resealed the toe brake master cylinders twice. Resealed the wheel cylinders. We are using a pressure pot with clear tubbing for bleeding. I have rigged a fitting to screw into the top of the reservoir to have pressure pushing the fluid from the top down. When bleeding from the wheel cylinders up I have the clear hose coming from the reservoir to a catch can to be able to watch for air. I have isolated the toe cylinders and they hold pressure. We have bled the system from he revivor down and from the wheel cylinders up. Probably 10 gallons of fluid each way. Have jacked the nose up putting the tail on the ground. the ground and tapped and wiggled everything that can move. I have worked the toe brakes and parking brakes while bleeding both ways. I can get all the air out of the lines and have fair brakes for a day or so then the brakes go spongy. When I look at the clear tube running from the tee at the toe brake cylinders I can see air. We will bleed the brakes from the wheels up and remove all the air ( pumping the toe brakes ) and again the air comes back. Neither toe cylinder shows fluid leaking. Nor do I see any signs of leakage on the lines going to the reservoir or the wheel cylinder. I am out of ideas. Has anyone seen the compression fittings on the clear tubing let air in and hold the fluid in? Or the toe cylinders? I feel its coming from that area as quickly as I see air in the clear line going to the reservoir. Thanks in advance. Milton Quote
Dom Posted June 11, 2020 Author Report Posted June 11, 2020 Just now, bradp said: Are your brake lines 40 years old? Just now, bradp said: Are your brake lines 40 years old? Which lines. The rubber hoses at the wheel cylinders are new. I forgot about that. The clear tubing is original. Quote
carusoam Posted June 12, 2020 Report Posted June 12, 2020 Welcome aboard Milton! You have done a great job describing the work you have completed... Got any additional pics you can post? Often somebody around here can recognize something in a pic that can be better... Best regards, -a- Quote
Marauder Posted June 13, 2020 Report Posted June 13, 2020 I am working on a M20K. We have resealed the toe brake master cylinders twice. Resealed the wheel cylinders. We are using a pressure pot with clear tubbing for bleeding. I have rigged a fitting to screw into the top of the reservoir to have pressure pushing the fluid from the top down. When bleeding from the wheel cylinders up I have the clear hose coming from the reservoir to a catch can to be able to watch for air. I have isolated the toe cylinders and they hold pressure. We have bled the system from he revivor down and from the wheel cylinders up. Probably 10 gallons of fluid each way. Have jacked the nose up putting the tail on the ground. the ground and tapped and wiggled everything that can move. I have worked the toe brakes and parking brakes while bleeding both ways. I can get all the air out of the lines and have fair brakes for a day or so then the brakes go spongy. When I look at the clear tube running from the tee at the toe brake cylinders I can see air. We will bleed the brakes from the wheels up and remove all the air ( pumping the toe brakes ) and again the air comes back. Neither toe cylinder shows fluid leaking. Nor do I see any signs of leakage on the lines going to the reservoir or the wheel cylinder. I am out of ideas. Has anyone seen the compression fittings on the clear tubing let air in and hold the fluid in? Or the toe cylinders? I feel its coming from that area as quickly as I see air in the clear line going to the reservoir. Thanks in advance. Milton I feel your pain Milton. I struggled to get mine back to normal after rebuilding the toe cylinders and replacing the brake lines. I’m convinced my issue was trapped air in the toe cylinders. One of the IAs on the field told me that when the toe cylinders are rebuilt it is best to load them up with fluid before installing them. I think what helped was Rich’s suggestion to fly up to 10k. It seemed to have made a difference. I never want to see another air bubble!Sent from my iPhone using Tapatalk Pro 1 Quote
carusoam Posted June 13, 2020 Report Posted June 13, 2020 @10k’ the bubbles should grow to be approximately 1.5X with the change in atmospheric pressure... Whatever helps get them to move... PP thinking out loud... Best regards, -a- Quote
Yetti Posted June 13, 2020 Report Posted June 13, 2020 Oil. Can from the bottom. 20 pumps should do it. We had to go forty on one side Quote
MooneyMitch Posted June 13, 2020 Report Posted June 13, 2020 Is you airplane equipped with co-pilot brakes perhaps? Quote
Hank Posted June 13, 2020 Report Posted June 13, 2020 My IA just rebuilt my brakes at April annual, after the right pedal went to the floor landing at his 3200' field. He never said anything about bleeding them being unusual, but I sure read about a lot of toil and trouble here. Maybe you should enlist some paid help? I like doing things myself, but like Clint says, a man's got to know his limitations. Quote
MooneyMitch Posted June 14, 2020 Report Posted June 14, 2020 My experience........ pilot and co-pilot brakes.......pumped and pumped and pumped fluid up from calipers...... stilll air in system and weak pedal. Problem was bad seal in left shuttle valve. Seal replaced..... problem solved. I hope this information helps. Quote
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