Brake dragging/not releasing

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taildragger
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Brake dragging/not releasing

Post by taildragger »

Hi. Issue with 1975 M5 brake. Planes sits. Everything fine. Pump brakes, all normal. Go fly, taxi in and left, pilot side, brake starts not releasing all pressure. Can barely roll it in hanger. It is not the caliper binding at the rotor. Is definitely seems to be the master cylinder not releasing all pressure. Sits for awhile and is fine. I never use the parking brakes and does not seem to be the tab. Ideas? Thanks

Scott

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Andy Young
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Re: Brake dragging/not releasing

Post by Andy Young »

Next time it happens, momentarily crack the bleeder valve at the caliper and see if it releases. That will help with the diagnosis.

yanknbank
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Re: Brake dragging/not releasing

Post by yanknbank »

If you are definitely sure it's not the caliper, there's only a couple more things it could be.

1. I've heard of instances where old brake line delaminates and creates a flapper valve inside the line while could restrict return flow. Probably not this.

2. 5606 is hygroscopic, so am old system is susceptible to corrosion. I don't know what master cylinders you have, but if you have enough gunk in your bore, it could cause a restriction. It could be the co pilots left brake also, even if you're only using the pilots side.

3. You may have a pinch in your hard line. It's letting fluid through on application, but the pressure is not high enough on the release to let it back. This would probably be under your gear leg fairing skin, just as it comes out near the caliper.

I wouldn't rule out the caliper though

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gdflys
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Re: Brake dragging/not releasing

Post by gdflys »

I've been fighting the same issue off and on for a while now. What makes you say it's not the caliper? When I rebuilt the caliper I took it all apart and cleaned it up including removing all the dirt deposits and 5606 residue outside of the o-rings. There was some pitting in the bore. I put new pads on it which helped keep the o-rings from getting out to the pitted area. Also cleaned up the guides and pins which both had some surface corrosion. I didn't have any problems after that for half a year or so but now it's gets starting to bind up again. I found the guides and pins stuck when I took the outer pads off to check it out and had to convince the pins loose. It had sat for a few weeks while I was away for some sim training. Cleaned those up again and so far so good. I'm planning to replace the pins with new that I have IF I can get the old ones removed without breaking the threads off in the caliper.
Greg Delp
1979 M-5-235C
CT
ATP, CFI, A&P/IA

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Mog
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Re: Brake dragging/not releasing

Post by Mog »

Failing brake hoses is a real thing. Didn’t really buy into it until somewhat recently. The internal hose fails and blocks the line so it can relieve pressure. I replaced a bunch of lines on one of my trucks for this problem

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Re: Brake dragging/not releasing

Post by netconn »

I had this problem on my Lancair years ago. The problem was the masters were not releasing the fluid all the way when the pedals let up. As the pads kept riding on the rotor the fluid heated up and expanded causing the pads to push harder, causing more heat, more expansion... On and on. I could release the pressure at the caliper bleeder to move the plane but that is not a fix. You need to make sure the plungers go up all the way, and the cylinders are clean, or the valve will not open to release the fluid back into the masters

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flyusn99
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Re: Brake dragging/not releasing

Post by flyusn99 »

I had a similar problem with my 1976 M-5-235. If you still have your parking brake all set up and connected (or even if you disconnected the cable) look at the top of the cylinder on the pilots side brakes where the rod comes out of the top of the cylinder. There was a lift tab that sits right above the cylinder on the shaft for the parking brake. On mine the shaft had scoring on it that tab would allow the tab to intermittently engage and lock the brake (even without the parking brake cable connected to the tab). That is the first place I would look. I would remove that tab, and frankly the entire parking brake set up. I have heard of this tab activating on landing and causing an unintentional ground loop. Just a thought..

James

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taildragger
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Re: Brake dragging/not releasing

Post by taildragger »

Thank you everyone for the ideas for things to look at. I think netconn has the most probable. I should have also mentioned when the plane is sitting and cold I can pump the brake repeatedly and it releases. When the brake is heated “warmed” is when the dragging issue shows up. I’m leaving for a few weeks but when I get back looks like I’ll pull that master cylinder off and see what I can. Thank you everyone.

Scott

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gdflys
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Re: Brake dragging/not releasing

Post by gdflys »

Follow up for my similar situation. Removed caliper and reamed out torque plate guide holes and caliper bolt holes as well as scotch bright on the anchor pins. Lubed pins with silicon dry lube and reinstalled after making sure both pucks moved freely in and out of calipers. Pumped up the brakes and they seemed to work ok with only slight drag. Went to fly and same left side started dragging again and got worse as it heated up. Next step is rebuilding the master cylinder I guess. I physically pull the tops of the brake peddles backwards to make sure the rod is fully extended and still no release.
Greg Delp
1979 M-5-235C
CT
ATP, CFI, A&P/IA

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