Brakes Locked Up

[gevertex]

23 hours ago, M20Doc said:

It should be under the floor on the pilot’s side.  You’ll have to remove the belly panel to access it.  Send me your logs and a picture for an entry when you get it working!!

Thanks! I’ll take a look and if I make any progress I’ll send you a note. I have someone coming Monday so I may just wait until then. 

[gevertex]

I wanted to update this group. The brakes were inspected by two different A&Ps and checked out ok. Parking brake checked out ok. Second A&P agreed the brakes were hard, recommended new rotors + brake lines.

[A64Pilot]

Sometimes if brakes have been overheated the pads can become hard / glazed and not have good friction.

I’ve not seen rotors glaze like pads can, but maybe?

If you change pads read on how to season them, but be careful with overheating, the idea is to transfer a layer of pad to the disks, as strange as that sounds.

Page 9 of the attached .pdf

https://www.groveaircraft.com/ica-wb.pdf

I’d remove and sand the rotors with a pad sander to slightly roughen them and remove the glaze before I bought new myself, unless of course they were worn, but if they were one of the A&P’s should have told you.

[gevertex]

Another update. At annual (with a 3rd shop A&P/IA), brake fluid was discovered to not have been fully flushed, was way overdue for a change. Fluid was described as gummy. Master cylinder needs to be rebuilt.

Ended up with 3rd shop as plane was in for avionics refit when annual expired. Good thing too as it looks like they found the problem. If it comes back working well then I likely found the problem.

 

I thought it had been flushed, but maybe not. Need to double check the logbooks.

[Ragsf15e]

2 hours ago, gevertex said:

Another update. At annual (with a 3rd shop A&P/IA), brake fluid was discovered to not have been fully flushed, was way overdue for a change. Fluid was described as gummy. Master cylinder needs to be rebuilt.

Ended up with 3rd shop as plane was in for avionics refit when annual expired. Good thing too as it looks like they found the problem. If it comes back working well then I likely found the problem.

 

I thought it had been flushed, but maybe not. Need to double check the logbooks.

Hopefully they are relatively Mooney Saavy because sometimes there are issues bleeding the brakes.  There are many “techniques” on this too… it brings out all kind of suggestions.  If your shop has smart skilled people they will probably be fine.  If there are issues with squishy brakes afterwards, ask here and we’ll get you squared away.

[DCarlton]

3 hours ago, gevertex said:

Another update. At annual (with a 3rd shop A&P/IA), brake fluid was discovered to not have been fully flushed, was way overdue for a change. Fluid was described as gummy. Master cylinder needs to be rebuilt.

Ended up with 3rd shop as plane was in for avionics refit when annual expired. Good thing too as it looks like they found the problem. If it comes back working well then I likely found the problem.

 

I thought it had been flushed, but maybe not. Need to double check the logbooks.

I didn't study your whole thread, but I had a similar problem a few years ago.  Brakes dragged or locked after landing (can't remember exactly).  Mechanic flushed the brakes and discovered the fluid to be thick and gummy.  After flush, no more issues.  

[A64Pilot]

Ref hydraulic fluid, decades ago the Military dropped the old standby 5606 and went to 83282 fluid. It’s a synthetic and is pretty much fire proof, but it’s real advantage is it doesn’t turn into a sticky, gummy mess over the years.

You can eliminate the gooey mess forever by changing to mil spec 83282, it’s completely compatible with all form of 5606, you can even use it to top off a system filled with 5606.

If your changing fluid you really should give it a look, it’s not much more expensive and is readily available.

https://www.aircraftspruce.com/catalog/lgpages/aeroshell08-14635.php

https://www.groveaircraft.com/fluid.html#:~:text=Bottom Line%3A MIL-H-,together without any ill effects.

83282 is good down to -40C, if you fly in colder than that then you need 87257, it’s good down to -57C.

‘I have no experience with 87257 we never flew in those kind of temps

[gevertex]

I got it back and brakes are spongy. They seemed to modulate better and I could stop the airplane fine, but had a hard time holding it during run up. Any tips?

[mcarterak]

Something isn't right if you can't hold it back for run up. I can do full power static takeoffs and the airplane doesn't budge. 

[carusoam]

Symptom of having air in the brake lines… squishy pedals.

Does the M20J have the brake fluid reservoir in the tail?  (LBs do)

The long distance from reservoir to brake cylinders may have an uphill location that has a tendency to catch a bubble…

Flushing the bubble out takes a minimal amount of know how…

May take two people to pump brakes, send a lot of fluid through the line, and close the line before air comes back in… 

Be on the look out for where that bubble lives…

Happiness is… a solid brake pedal.

PP thoughts only, not a mechanic…

Best regards,

-a-

 

[Pinecone]

Bubbles in line from reservoir to master cylinder does not make mushy pedals.  Until the bubble gets pushed to the master cylinder

[gevertex]

Looks like the shop will take a look at it again this week. Hopefully more bleeding as suggested will take care of it.

[gevertex]

Wanted to provide an update on this. Shop found significantly over due brake fluid which was likely the culprit. Described the consistency as like honey.

Here was the work done to get it working like new:

• Rebuilt all master and slave cylinders
• Replaced brake pads
• Replaced brake discs with Black Steel
• Flushed fluid fully (removed all fluid and replaced with new)
• Bled brakes 2x (first time pedals were mushy, second time worked like a charm)

Brakes are now very effective.