colin_eyres Posted October 24, 2021 Report Share Posted October 24, 2021 hi, is there anyone out there who has had a similar problem to me and what was done to diagnose the problem and what was the fix? the aircraft in question is a 2007 ctsw which has been kept in pretty good condition for a syndicate aircraft with some 2300hrs on the airframe but only 250hrs on the replacement new engine.recently the aircraft was in for some carbon fibre work on one of the wings and the guys who did it did a fantastic job.now due to covid etc the aircraft was not flyable for more than 2 months and when the aircraft came back everything was fine and the aircraft has about 10hrs more flying time added due to other members using it.yesturday it was my turn to fly and i rolled her out of the hangar onto the apron to do my checks.I tried setting the parking brakes and noticed the feel of the lever didnt feel right and the travel of the lever seem to be reduced in length also.when checking whether the parking brake was holding i found that out that it wasnt. I then tried to see if the brakes would hold just using the brake lever in the normal fashion and found that the lever action was fine and yes the brakes held just like the should.when i was ready to fly at normal tickover the aircraft was constantly creeping foward and on re applying the parking brake several times it appeared to hold for about three seconds then started creeping again. when i was ready for a power check I just held the brakes by hand and the aircaft held fast at full power.so my conclusions are that brake pads are ok,it dosnt feel if there's any air entered the system?, due to the limited reservoir capacity and the amount of brake usage then there's not going to be a leak in the system either.the braking system itself has never shown any signs of leakage or any other problems ever.i removed the centre cover to expose the parking brake mechanism but there was nothing obvious. any thoughts on the matter guys? Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 24, 2021 Report Share Posted October 24, 2021 Bleed the brakes and look for the telltale signs of fluid trails, especially around the brake caliper pistons. Make sure the brake nipples are closed properly. Look for leaks around the master cylinder. Check to see if the hoses have been runbed through where it passes through the aircraft hull. And since it's a CTSW, check the brake lines for crazing or fracturing where they run down to the brakes, I had lines burst on an old CTSW. Brake leaks don't usually squirt unless it's been badly neglected. They're slow and small, and appear when pressurized. This is the first sign of seal failure. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted October 24, 2021 Report Share Posted October 24, 2021 If the brakes hold and the lever doesn't continue to move back while holding pressure, I would suspect either the parking brake valve, or the check valve. If the lever move back when held look for a leak, and if there are none replace the master cylinder, because it is leaking internally. Quote Link to comment Share on other sites More sharing options...
colin_eyres Posted October 24, 2021 Author Report Share Posted October 24, 2021 hi, where would the check valve be located and what is its function? my money is on the parking brake valve as the brake lever feel and brake efficiancy is perfect in normal taxiing/power runup situations. Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 24, 2021 Report Share Posted October 24, 2021 Above the master cylinder in your first picture. Just under the lever. 2007 models also might have a check valve further back just before the t split to the calipers. If that valve has failed, it's not possible to set the parking brake there either. Edit: see attached. 7257D Quote Link to comment Share on other sites More sharing options...
Anticept Posted October 24, 2021 Report Share Posted October 24, 2021 Also why is your fluid green? Did someone put in DOT brake fluid? And I reiterate to bleed your system, your intake line looks empty. A lot of air in the system will make it very hard to set the parking brake. The stroke length of the brake is quite short in a well bled system, around a third to halfway depending on the brake system, and it should rapidly build resistance, not feel like you are compressing air. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted October 24, 2021 Report Share Posted October 24, 2021 1 hour ago, colin_eyres said: hi, where would the check valve be located and what is its function? my money is on the parking brake valve as the brake lever feel and brake efficiancy is perfect in normal taxiing/power runup situations. Okay, a quick explanation on the brake system. The forward fitting on the mater cylinder is connected to the brake reservoir in the baggage compartment. The outlet side of the master cylinder has a "T" fitting that one leg goes to the brake cylinders and the other to the parking brake valve. The line then goes through the check valve, and on to another "T" fitting. One side of this "T" fitting goes to the other side of the parking valve, and the other continues on to another "T: fitting. This "T" fitting is where it splits and goes to the individual wheels. For normal operation when you pull the brake the fluid goes through the check valve and return through the parking brake valve. When you turn on the parking brake valve it blocks the return of the fluid, so when you pull the brake lever the fluid flows out through the check valve and can not return through the closed parking brake valve holding pressure on the brakes at the wheels. As Corey said it looks like the fluid is the wrong color in the brake lines. For the US market we use the standard red MIL 5606 hydraulic fluid. I'm not sure what kind of repairs you had done, but if the brake system was opened up it is possible that the wrong fluid was put back in. If so it could be wreaking havoc on the seals causing the issues you are having. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted October 25, 2021 Report Share Posted October 25, 2021 I see you're from England. I hope that greenish fluid in the brake lines are the US equivalent to 5606 fluid. The guys comment on fluid color is a good check. It should be red. 5606 hydraulic brake fluid. It is fairly standard. If it is DOT 4 or the equivalent it may have degraded some seal. I have seen DOT 4 in the US destroy master cylinder seals. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted October 25, 2021 Report Share Posted October 25, 2021 The cost of the Marc master cylinders will make your eyes water if you need to replace. I don't know if it's an option legally or shipping-wise where you live, but I'd highly recommend a Matco cylinder as a replacement if you can. It's around 1/4 - 1/3 the price, and is pretty much a drop in swap. My Marc cylinder failed at about 150 hours, I replaced with a Matco and it has worked like a champ almost 800 hours so far. Quote Link to comment Share on other sites More sharing options...
colin_eyres Posted November 8, 2021 Author Report Share Posted November 8, 2021 Hi guys, I'd like to thank you for help so far on this topic, firstly I'd like to respond to Anticept and Roger Lee about the colour of the brake fluid.I've taken advice from one of the UK's top maitainance guys and he assures me that the green coloured fluid is correct for UK specced aircraft.when pressed further about what type of fluid it was he told me that it was a mineral oil based fluid and could be bought under the name of LHM.anyway we finally got to the aircraft yesturday to have a good look around. the first thing that was noticed was the master cylinder reservoir was empty and the pipe leading off from it was half empty also.and in the centre tunnel there was a very small hardly moist oily residue, the calipers and nipples were bone dry. we had decided prior to arriving at the aircraft that we would fit a new parking brake valve and what with finding the oily residue we proceeded to fit the new valve.now there was 2 off us there and both of us had experience with bleeding motorbike and car braking systems. firstly when trying to add fluid to the reservoir using a funnel it was noted that the fluid would just sit in the funnel and not replenish the master cylinder. i decided to open the caliper bleed nipple a crack whist my buddy operated the brake lever. we got a few bubbles out of the system that way on each wheel but we were not getting enough fluid into the brake lines that way. we tried ever so many times but no joy.I even adapted a foot pump to gently add pressure to force the fluid out of the reservoir and down the pipes still no joy.so in a nutshell we have a mega amount of air in the system and what ever method we use to evacuate it it just refuses to budge and the air bubble just moves back and forth as you operate the lever.is back filling the lines a good idea? so what do you guys do to change the brake fluid and remove the air bubbles TIA Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted November 8, 2021 Report Share Posted November 8, 2021 You always try to flush brakes from the bottom up and do it on each side. I just take a small pump up bug sprayer, unscrew the nozzle right at the sprayer outlet. Then buy some clear poly hose and slip it over it. Then I put my brake fluid in it. Pump it up and when I squeeze the sprayer handle that fluid fly's through the brake tubing flushing out all air. I also take an empty water bottle and tape a small poly hose in the mouth and slip that over the reservoir tip so the flushing brake fluid just runs over into the bottle. No mess and makes brake bleeding easy. found things like an oil can when you try to do the same thing is so slow you don't always get the air out. There's an old picture of it somewhere on this website. Quote Link to comment Share on other sites More sharing options...
Anticept Posted November 8, 2021 Report Share Posted November 8, 2021 Mineral oil is the correct base for the hydraulic fluid. I would still press for standards and double check to be sure that it's compatible so that you know what to look for in the future. As for the bleeding process, I have nothing to add! Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted November 8, 2021 Report Share Posted November 8, 2021 I used to use a home made unit like Roger, but the internals got all warped out of shape from the fluid. I was to lazy to make up a new one so I ordered this from Aircraft Spruce. https://www.aircraftspruce.com/catalog/lgpages/hydraulicBleedertank.php Quote Link to comment Share on other sites More sharing options...
BravoFoxtrot Posted November 8, 2021 Report Share Posted November 8, 2021 I found an article on the LMH fluid. This comparison chart was part of the article: A comparison of MilSpec 5606(H) and LHM+: Seal compatibility - fine Non-foaming under high pressures - fine Viscosity/temperature stability - acceptable Lubrication qualities - fine Corrosion resistance- fine Volatility - passable Resistance to thermal breakdown - fine Looks like there should be no issues. For bleeding the brakes I have used the base of a Coleman lantern with the lantern parts removed and a valve with tubing installed. You fill the reservoir with your brake fluid, use the pump on the lantern base to pump up the pressure, then open the valve to let the brake fluid in the reservoir flow into the brake bleeder on the caliper. Quote Link to comment Share on other sites More sharing options...
colin_eyres Posted November 22, 2021 Author Report Share Posted November 22, 2021 Hi guys for all your advice.i decided to rig up some devices based on Rogers post, but as we had already changed the park brake valve firstly it was time to have a look at the check valve this time around.on removal and close inspection of the valve seating it was discovered that there was some contamination visible stopping the valve seating properly.we duly fitted a new check valve and almost straight away we noticed a improvement even though there was masses of air in the system still. with perseverance we managed to purge the air from the system and all is now fine. on getting home to tear down the check valve to see what the contamination was I found it was actualy part of the O ring that had some how got stuck in the seating and was the cause of our problems.this was the original 2007 check valve and w'ed never had a problem with it. thanks again Quote Link to comment Share on other sites More sharing options...
Mike Koerner Posted December 22, 2022 Report Share Posted December 22, 2022 I just replaced my parking brake valve. This discussion was very helpful. Thanks to all who contributed. My parking brake was holding fine, but it was leaking fluid through the stem, which was gumming up my tunnel and requiring periodic fluid refills. Relating to a previous discussion on plane-to-plane variations: my 2004 CT2k doesn't have the check valve shown in the manual (its manual), and I don't believe it ever did. What does that mean for brake operation? The brakes function exactly the same except if my parking brake valve is closed before the brakes are applied (perhaps by a fidgety passenger?) then I won't be unable to use the brakes, at all, until I figure out the problem and open the valve back up. That could make for an exciting rollout. On the other hand, leaving the check valve out of the system removes 6 potential leakage joints; the potential failure of one mechanical part; the weight and cost of the check valve, a "T" fitting, the fluid in the bypass line and the bypass lines themselves; and, perhaps most importantly, it makes the system easier to purge. Frankly, I can't see how air trapped in the bypass line below (downstream) of the check valve ever gets out of the system, though I will grant that it doesn't seem to present a problem based on all of your collective experience. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted December 22, 2022 Report Share Posted December 22, 2022 21 minutes ago, Roger Lee said: Hi Mike, Your brakes are just like other CTSW's and LS's. From the picture Mike posted, they are not the same. If the valve is turned on without pressure, and you pull the handle all it will do is apply pressure to the valve, not the brakes. On his to lock the brakes you have to apply pressure, and close the valve. It doesn't have the added circuitry of the brake system that the CTSW and LS have. Quote Link to comment Share on other sites More sharing options...
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