Marauder Posted December 1, 2018 Report Share Posted December 1, 2018 I’m hoping one of you brake gurus or connoisseurs can shed some light on brake bleeding. Go to the last 3 paragraphs for short story. Terry and I worked on my brake rebuild today. The right brake failure to return which I thought may have been a sloppy brake was actually a linkage issue that Terry corrected. Since I had new brake lines and the kit to rebuild the leaking parking brake and Terry didn’t have the time to rebuild the masters and do the brake caliper rotations, we decided to concentrate on fixing the leaks and replacing, what turned to be original 1975 brake lines. As a smart IA, somehow Terry convinced me to pull the parking brake while he worked on the brake lines. Not a pretty sight seeing a guy my size squeeze into a wheel well. But the big guy did get it out. Interesting to see that even in 1975 we were using stuff that was made in China. The parking brake rebuild went well. 3 O rings and it went back together fine. As did the reinstall, despite a few expletives that would have Bob B scratching his head. Here is the need for the guru part. Terry and I rigged a system to pull new fluid up through the reservoir. The process went well, expect for the fact the fat old guy was on the ground opening the valve and supplying the fluid while the young IA got to do the vacuum gizmo on his two feet. After not seeing anymore air, we pumped up the brakes. They felt okay but certainly weren’t solid like I have felt previously. Terry decided to give the old fat guy a brake (pun intended) and he was using a syringe to push fluid up from the calipers through the reservoir. That seemed to work well but on the last syringe full, he couldn’t push anymore fluid. It was like it was air-locked. We decided to do the other side and the exact same thing happened. After several syringe full of hydraulic fluid being pushed, it wouldn’t take anymore. We discussed several “theories” including something happening to the parking brake, the calipers holding air and locking the flow or somehow some unknown containment blocking both lines. That last one is up there with the odds of me selecting the right Powerball numbers tonight. Any thoughts? Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
Andy95W Posted December 1, 2018 Report Share Posted December 1, 2018 Any chance you were trying to turn on the cabin heat but pulled the parking brake lever by accident? 1 1 Quote Link to comment Share on other sites More sharing options...
Andy95W Posted December 2, 2018 Report Share Posted December 2, 2018 You guys probably already thought of this, but did you take the cap off the reservoir to ensure the air hole wasn't blocked by some foreign matter? Also, what happens if you crack open one of the bleeder bolts? Does fluid shoot out under pressure or just dribble? You don't have to worry about introducing air into the system, gravity will pull the fluid out from the top of the system down. And are you sure the brake pedals were completely released? Quote Link to comment Share on other sites More sharing options...
Marauder Posted December 2, 2018 Author Report Share Posted December 2, 2018 You guys probably already thought of this, but did you take the cap off the reservoir to ensure the air hole wasn't blocked by some foreign matter? Also, what happens if you crack open one of the bleeder bolts? Does fluid shoot out under pressure or just dribble? You don't have to worry about introducing air into the system, gravity will pull the fluid out from the top of the system down. And are you sure the brake pedals were completely released? Hey Andy. Thanks for the reply. We made a plug with an adapter for a vacuum bleeder for the top of the reservoir and were feeding fluid in from the bottom up. This got us to semi solid brakes and that is when Terry tried pushing fluid up through the caliper’s bleeder bolts. That is when we saw the strange fluid lock-up. When you say “the brake pedals were completely released”, what did you mean?Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
Marauder Posted December 2, 2018 Author Report Share Posted December 2, 2018 Any chance you were trying to turn on the cabin heat but pulled the parking brake lever by accident? I probably would not have bothered with the parking brake other than the fact it was clearly leaking. And on my plane, yes indeed, the parking brake and cabin heat are right next to each other Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
orionflt Posted December 2, 2018 Report Share Posted December 2, 2018 Chris, When I back bleed brakes i just use an old style pump oil can with a hose attached to the bleeder valve. once I hit the point where it looks like the air is out I will cycle the brakes for several minutes, then I bleed them normally. haven't had much of an issue with this method. Brian Quote Link to comment Share on other sites More sharing options...
Andy95W Posted December 2, 2018 Report Share Posted December 2, 2018 7 minutes ago, Marauder said: When you say “the brake pedals were completely released”, what did you mean? That the pistons in the master cylinders had returned to their full extended position. 1 Quote Link to comment Share on other sites More sharing options...
Marauder Posted December 2, 2018 Author Report Share Posted December 2, 2018 Chris, When I back bleed brakes i just use an old style pump oil can with a hose attached to the bleeder valve. once I hit the point where it looks like the air is out I will cycle the brakes for several minutes, then I bleed them normally. haven't had much of an issue with this method. Brian That’s what we we were doing Brian, but at some point it just wouldn’t allow any flow through the system on either side. It was like there was a common blockage. Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
orionflt Posted December 2, 2018 Report Share Posted December 2, 2018 try doing a normal bleed of the brakes after it sits overnight. make sure you pump the brakes several times to build up max pressure before opening the bleeder. I am curious how much fluid bleeds and with how much pressure. you can call me while you are working on it if you want. I would come over but my day is going to be a bit busy. if you feel that the brakes work well enough to be safe you can come over to UKT if you want. I will be there after around 12. Brian Quote Link to comment Share on other sites More sharing options...
Marauder Posted December 2, 2018 Author Report Share Posted December 2, 2018 try doing a normal bleed of the brakes after it sits overnight. make sure you pump the brakes several times to build up max pressure before opening the bleeder. I am curious how much fluid bleeds and with how much pressure. you can call me while you are working on it if you want. I would come over but my day is going to be a bit busy. if you feel that the brakes work well enough to be safe you can come over to UKT if you want. I will be there after around 12. Brian Describe what you consider to be a normal bleed please. We were doing a bleed from the top using a vacuum bleeder with the new supply being pulled in from the bottom. That worked okay but the pedals were still a little soft. That is when we tried pushing fluid up from the bottom using a syringe attached to the caliper bleeder and it worked a few times on each side and then locked up hydraulically. Terry is doing a charter tomorrow and said he would try to come over to try again in the afternoon. If that doesn’t work, I may need to see if you can help later this week. Terry is off to get a type rating of some kind starting next week. Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
orionflt Posted December 2, 2018 Report Share Posted December 2, 2018 one person pumps the brakes to ensure pressure is built up (3-4 times) then hold them applied, the second person will open the bleeder with pressure applied. the brake pedal will get soft and depress as fluid bleeds off, close the bleed valve before releasing the the brakes. do this until brakes no longer feel spongee. make sure you keep the reservoir topped off. Brian 1 Quote Link to comment Share on other sites More sharing options...
orionflt Posted December 2, 2018 Report Share Posted December 2, 2018 one technique i use to help keep from getting air pulled back in if the person on the brakes accidentally lets up on the brakes is to put a piece of tubing on the end of the bleeder, then put the end of the tubing in a cup of hydraulic fluid. the air bubbles will exit but not be drawn back in. 1 Quote Link to comment Share on other sites More sharing options...
Yetti Posted December 2, 2018 Report Share Posted December 2, 2018 I pulled from the top with a vacuum pump. The push from the bottom with an oil can Last time it took 40 pumps. Pump 20 times rapidly. Person should watch resivoir for overflow and air bubbles. 1 Quote Link to comment Share on other sites More sharing options...
Marauder Posted December 5, 2018 Author Report Share Posted December 5, 2018 I wish I could report the end of Part Deux as a complete success. Unfortunately not. There will be a Part Trois. Part Deux has been frustrating since the solution looked like was a done deal only to have those hopes squelched. So let's see where we left our intrepid explorers at. We had successfully replaced both flexible brake lines in the wheel wells. We rebuilt the parking brake and were in the process of bleeding the system. We made an adapter for the reservoir and attempted to bleed the brakes using a vacuum system at the reservoir end. This seemed to work well but the brakes still felt a bit soft. So, we decided to push brake fluid up through the bleeder into and out of the reservoir. This too seemed to work until the point where we could not push anymore fluid through. It was like there was a hydraulic lock and to make things worse, both sides were doing this. Armed with the local shop's pressure pot and hand pump "oiler", we attempted to bleed the brakes again on Monday night. The hand pump was slowly pushing fluid into the system from the bleeder but it was not moving too fast. We repeated this with the pressure pot and although we were seeing a steady flow, we were seeing a Congo line of air bubbles coming out of the reservoir. We suspected the pressure pot and/or the bleeder valve was intermittently allowing air into the system. Part Trois will be to try another pressure pot and to replace the bleeder valves. Frustrating to say the least. Here is the picture of the Congo line of bubbles. Quote Link to comment Share on other sites More sharing options...
M20F-1968 Posted December 5, 2018 Report Share Posted December 5, 2018 I know nothing about this since I do not have a shuttle valve in my system, but some Mooneys have a shuttle valve that separates the left and rgt brakes. I do not know if you have dual brakes either, but if you do, it might be worth considering if there is a shuttle valve in place. John Breda 1 Quote Link to comment Share on other sites More sharing options...
Yetti Posted December 7, 2018 Report Share Posted December 7, 2018 Did you replace the mushy line between the reservoir and the parking brake valve. Get rid of you contraption and just look for bubbles in the reservoir. Quote Link to comment Share on other sites More sharing options...
Marauder Posted December 7, 2018 Author Report Share Posted December 7, 2018 Did you replace the mushy line between the reservoir and the parking brake valve. Get rid of you contraption and just look for bubbles in the reservoir. Yep, new line between reservoir and parking brake valve. Have not looked into the reservoir but will do so before the next attempt. Sent from my iPad using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
Yetti Posted December 7, 2018 Report Share Posted December 7, 2018 It grump IA said it usually takes 20 rapid pumps. the last time it took 40 rapid pumps. Medium size oil can 1 Quote Link to comment Share on other sites More sharing options...
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