Fritz1 Posted Monday at 07:32 PM Report Posted Monday at 07:32 PM bleeding brakes on the Bravo one more time, either did not get all the air out or air is getting in somewhere, pilot masters got rather soft again, think air bubbles still lodged in the piston assemblies, in particular in the check valves, will take rear of masters loose and drop the rear down and turn fittings up while bleeding from the wheel calipers, tap the masters to shake any bubbles loose, here is my question: the plug of my brake fluid reservoir in the tail cone does not have a vent hole and I am wondering if this might be part of the problem, air might just be creeping through the master cylinder seals during a descent augmenting any residual bubbles in system, soo, is there any reason why the brake fluid reservoir plug would not have a vent hole???
IvanP Posted Monday at 07:52 PM Report Posted Monday at 07:52 PM If you have the dual puck brakes on your Bravo, you may want to check your brake linings. I have been chasing similar issue on my Bravo last year. One side would just be soft and I had to pump the brakes couple of times to get good braking action. Inspection did not show any leaks. Bled the brakes 3 times to no avail. Always tested good in the hangar while bleeding, but then got soft again on taxi. Then I noticed that my brake linings were a bit thin on the affected side and the caliper had to travel to the point that it would push against the middle gear door (there is very little celarance there). The door would flex enough to allow the brake to bite, but then the pressure would push the caliper back in, hence the need to give it couple of pumps for the brakes to be firm. Replaced the linings and the caliper is now not touching the door when brakes are applied. All is good now. Because you need to remove the middle doors to get to the brake caliper, I did not spot the problem until I had someone apply the brakes while I was watching the caliper movement without removing the middle doors.
Fritz1 Posted Monday at 08:05 PM Author Report Posted Monday at 08:05 PM interesting, but brake linings are brand new, replaced in spring of last year, think this is the fourth time I am bleeding brakes, resealed the pilot masters, no fluid leaking anywhere
IvanP Posted Monday at 08:55 PM Report Posted Monday at 08:55 PM (edited) Strange. I would still check the clearance betwen the middle doors and caliper when applying brakes to see how much clearance you have there. Also, check the bleeding procedure for dual brakes. There is a shuttle valve between the pilot and co-pilot side. Edited Monday at 09:20 PM by IvanP
PT20J Posted Monday at 09:40 PM Report Posted Monday at 09:40 PM As the pads wear the fluid level will drop in the reservoir and air needs to get into the reservoir or suction will be created. The fluid level also drops slightly when the brakes are applied. The plug on the reservoir of my M20J has a small vent hole. It is possible for air to pass through an opening too small for fluid to leak.
Fritz1 Posted Monday at 10:13 PM Author Report Posted Monday at 10:13 PM thank you, that is what I thought, this may be part of the reason why my brakes are mushy, my plug with the vent hole must have gone under and been replaced with a non-vented plug at some point in time, will either buy reservoir plug with hole or drill small hole into existing plug,
IvanP Posted Monday at 10:32 PM Report Posted Monday at 10:32 PM To determine if the plug is the issue, you can just take the plug out and taxi around to check if the brakes are still soft. I seem to recall that my plug has a small hole in it. 1
LANCECASPER Posted Monday at 11:24 PM Report Posted Monday at 11:24 PM 3 hours ago, Fritz1 said: bleeding brakes on the Bravo one more time, either did not get all the air out or air is getting in somewhere, pilot masters got rather soft again, think air bubbles still lodged in the piston assemblies, in particular in the check valves, will take rear of masters loose and drop the rear down and turn fittings up while bleeding from the wheel calipers, tap the masters to shake any bubbles loose, here is my question: the plug of my brake fluid reservoir in the tail cone does not have a vent hole and I am wondering if this might be part of the problem, air might just be creeping through the master cylinder seals during a descent augmenting any residual bubbles in system, soo, is there any reason why the brake fluid reservoir plug would not have a vent hole??? Bleeding the brakes on a Mooney is a challenge and there has been a lot written about it on Mooneyspace: https://mooneyspace.com/search/?q=BLEED BRAKES&quick=1&updated_after=any&sortby=relevancy&search_and_or=and Maxwell, Kendrick, Dugosh and others can do it successfully every time only since they've done it so many times and figured out what works and what doesn't.
kortopates Posted Tuesday at 12:12 AM Report Posted Tuesday at 12:12 AM Strange. I would still check the clearance betwen the middle doors and caliper when applying brakes to see how much clearance you have there. Also, check the bleeding procedure for dual brakes. There is a shuttle valve between the pilot and co-pilot side. Actually only the Vintage Mooney’s use a shuttle valves. Mooney eliminated them somewhere between Vintage and Modern models changing to running the copilot brakes in series with pilot brakes.Standard Mooney brakes are no harder to bleed than any other GA brakes and best bled as instructed in the service manual with a pressure pot bottom up just like other GA aircraft.It’s the dual brakes that are bare to bleed that there is so much written about here in older threads including by myself.The reservoir plug is vented. i don’t no where to get a proper replacement other than salvage.Sent from my iPhone using Tapatalk 2
IvanP Posted Tuesday at 01:28 AM Report Posted Tuesday at 01:28 AM 1 hour ago, kortopates said: Actually only the Vintage Mooney’s use a shuttle valves. Mooney eliminated them somewhere between Vintage and Modern models changing to running the copilot brakes in series with pilot brakes. According to the IPC, some Bravos had shuttle valve on dual brake installation (s/n 27-0108 to 27-0143). 1
PT20J Posted Tuesday at 02:06 AM Report Posted Tuesday at 02:06 AM Assuming that you have the cylindrical reservoir with the pipe plug at the top, the part number for the plug is 850009-000. It appears to be a standard pipe plug with a small hole drilled in it to vent the reservoir. I would call Frank Crawford at Mooney and see if he would share the drawing or at least tell you the size of the plug and the hole. I'm certainly not an expert on Mooney brakes but last year I did remove both master cylinders for rebuild and I replaced all the hoses in the brake system. So, I had all the plumbing pretty well opened. My A&P suggested opening the bleeders on both calipers and letting the system drain by gravity while occasionally slowly exercising the brake pedals. I ran about a pint of fluid through the system this way. Then we bled it bottom up with the A&P at the bleeders and me suctioning out excess fluid at the reservoir with a turkey baster. We did this until there were no more bubbles evident in the plastic line to the reservoir. It didn't take much and the brakes have been rock solid ever since. 3
skykrawler Posted Tuesday at 12:22 PM Report Posted Tuesday at 12:22 PM My memory tells me the plug is drilled from the bottom to about half way up the 'flats' then drilled from the side of one flat to intersect. Something like 1/32 inch hole.
Fly Boomer Posted Tuesday at 01:10 PM Report Posted Tuesday at 01:10 PM 11 hours ago, PT20J said: It didn't take much and the brakes have been rock solid ever since. Do you have brakes on the passenger side?
Fritz1 Posted Tuesday at 03:36 PM Author Report Posted Tuesday at 03:36 PM Thank you everybody, yes my plug is solid, no hole, think airplane came with it SN 280, do not think it got swapped while I owned the plane, will bleed the brakes one more time over the holiday, got 3 or 4 qts 5606, two bleeder pots, all kinds of lines and fittings, bleed back and forth, one pot at the wheel caliper one pot at the reservoir, max 35 psi, the masters are parker hannifin 24D, I have a set of spares, will open one of them to understand the piston mechanism, think there is a check valve in the piston since the piston does not move over the supply port, fittings are tilted sideways, that is part of the problem, will take the back of the masters off to tilt fittings up and then pump by hand, think this is the fourth time I am doing this, somewhat determined to get it right now 1
PT20J Posted Tuesday at 04:08 PM Report Posted Tuesday at 04:08 PM 2 hours ago, Fly Boomer said: Do you have brakes on the passenger side? No, pilot’s side only. 1
Fritz1 Posted Tuesday at 05:17 PM Author Report Posted Tuesday at 05:17 PM brakes on both sides, pilot side and passenger side
LANCECASPER Posted Wednesday at 11:26 PM Report Posted Wednesday at 11:26 PM Thank you everybody, yes my plug is solid, no hole, think airplane came with it SN 280, do not think it got swapped while I owned the plane, will bleed the brakes one more time over the holiday, got 3 or 4 qts 5606, two bleeder pots, all kinds of lines and fittings, bleed back and forth, one pot at the wheel caliper one pot at the reservoir, max 35 psi, the masters are parker hannifin 24D, I have a set of spares, will open one of them to understand the piston mechanism, think there is a check valve in the piston since the piston does not move over the supply port, fittings are tilted sideways, that is part of the problem, will take the back of the masters off to tilt fittings up and then pump by hand, think this is the fourth time I am doing this, somewhat determined to get it right nowI doubt that the solid plug is correct. Mine was made in 2008 and had a vented plug
Fritz1 Posted Thursday at 01:27 AM Author Report Posted Thursday at 01:27 AM Having 1/32" hole drilled into existing plug bottom up to connect into transversal hole
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