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Brake sticks when hot

jwilbur

Well Known Member
About to do some maintenance on my RV10 and have an issue I'd like to address.

Last year I over-heated my right brake and an O-ring failed. Ever since replacing the O-rings my right brake sticks pretty badly when hot. When cool I can apply the brake and release and no problem. After a flight, pushing back into the hangar is very difficult. I remember taking note when I replaced the O-rings last year that the center piston seemed pretty tight. I'm guessing something got deformed a little during my over-heat event and now when things get hot and expand the piston doesn't want to go back in. Once it all cools down everything is great again.

Anybody have some advice? Preferably something that doesn't involve replacing the whole brake assembly. These are matco brakes, by the way.
 
You sure that the replacement oring was the same size as original? If it is too thick, I would expect issues like you describe. Would also check for warpage of the rotor (i.e. parallelism relative to rotation centerline. Warpage is common after overheating, at least on automotive rotors.

I would also call matco or Grove to ask about the likelihood of deformation from an overheating event.

Larry
 
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Try bleeding the brakes. If you've got an air bubble trapped near the caliper, it will heat-soak and try to expand when you land and use the brakes. The air will try to expand a great deal more than the same quantity of brake fluid, and will exert pressure on the caliper, causing it to continue to drag.

That may not be your problem - but it will certainly cause your symptoms and it's easy to check.
 
Try bleeding the brakes. If you've got an air bubble trapped near the caliper, it will heat-soak and try to expand when you land and use the brakes. The air will try to expand a great deal more than the same quantity of brake fluid, and will exert pressure on the caliper, causing it to continue to drag.

That may not be your problem - but it will certainly cause your symptoms and it's easy to check.

At it's fully retacted state, a master cylinder will be open to the reservoir side. This function allows the caliper piston to retract after braking. Any expanding air will push fluid toward the reservoir. That said, many have found the matco m/c to have a bit weak of a spring in it. If the shaft is not fully reaching the retracted position, it does not open the circuit. This is typically seen as dragging brakes. I added helper springs to both my RV's to avoid this problem. Given the onset after an overheat event at the calipar, I would be looking at the calipar and rotor first. THe next time it drags, you can pull back on the brake pedal. If it moves a bit, that was your issue. If it is firm, it was not your issue.

Larry
 
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Brake sticking

We have had this problem with many RVs and a few Glastars using Matco's at my airport. Changed many O rings and warn overheated brake shoes, I Also have it now in my RV10. Matco master cylinder is causing the left brake to stick. It stops releasing completely and drags a brake so by the time you taxi back to your hangar or landing etc. its hot and very draggy . I've reach down and lifted my pedal and it releases .We've added out side springs , rebuilt them but nothing seems to work long term except a new replacement .
The majority of us have replaced them with Grove masters. There's really nothing wrong with the Matco calipers just their Master cylinders.
 
At it's fully retacted state, a master cylinder will be open to the reservoir side. This function allows the caliper piston to retract after braking. Any expanding air will push fluid toward the reservoir. That said, many have found the matco m/c to have a bit weak of a spring in it. If the shaft is not fully reaching the retacted position, it does not open the circuit. This is typically seen as dragging brakes. Given the onset after an overheat event at the calipar, I would be looking at the calipar and rotor first.

Larry

Definitely not the master cylinder. I've got external springs and I've manually checked. Pretty sure my issue is at the caliper.
 
Another thing to check - is caliper binding and not floating on the spindle mounts? Unlikely, but possible caliper housing got warped during overheat incident. Could also be a mount ware or lube issue.
 
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Make sure the piston puck is installed correctly and not reversed. The O ring on the piston should enter the caliper on the short side of the piston first. Also check to make sure the o ring did not roll and twist. They can develop a flat side on the cylinder side over time.
 
Check the torque of the caliper bolts. If they are over tightened, the caliper casting can warp, and possibly be a source of binding.
 
About to do some maintenance on my RV10 and have an issue I'd like to address.

Last year I over-heated my right brake and an O-ring failed. Ever since replacing the O-rings my right brake sticks pretty badly when hot. When cool I can apply the brake and release and no problem. After a flight, pushing back into the hangar is very difficult. I remember taking note when I replaced the O-rings last year that the center piston seemed pretty tight. I'm guessing something got deformed a little during my over-heat event and now when things get hot and expand the piston doesn't want to go back in. Once it all cools down everything is great again.

Anybody have some advice? Preferably something that doesn't involve replacing the whole brake assembly. These are matco brakes, by the way.

I have Matco brakes and went through a similar exercise this past year.

There are two pairs of bushings that can warp if the bolts are over torqued and they get hot.

The rotor can warp too if over heated. They are easy to check on a flat surface.

I know this is obvious, make sure you get all the brake dust cleaned off. The pistons can get rather nasty over time.

The other issue is side loading on the master cylinders, which is common in RVs. I had a recurring issue with my left brake. It turned out to be the master cylinder on the pilot side. It turned out that the rudder pedal frame was out of square a bit. For $13 you can rebuild the cylinder. All had to do was add a washer or two to correctly plumb the cylinder.

It?s frustrating to troubleshoot, but I?ve learned more about brakes in the last six months than I ever thought I could learn. Both Andy and George (Matco) were great in helping me with the issues.
 
Looks like it is a hydrolic issue. I went for a flight and when I got back the brake was stuck as usual when it's hot. While hot I opened the bleeder valve. Fluid shot out and the brake immediately released. I've been in touch with George from Matco. This was his suggestion to help narrow down the problem.

Next, I'll get it hot again and start opening up other parts of the system to see what's not working correctly.
 
Looks like it is a hydrolic issue. I went for a flight and when I got back the brake was stuck as usual when it's hot. While hot I opened the bleeder valve. Fluid shot out and the brake immediately released. I've been in touch with George from Matco. This was his suggestion to help narrow down the problem.

Next, I'll get it hot again and start opening up other parts of the system to see what's not working correctly.

This confirms that the bleed opening hole is not being uncovered. Just find out why. If your external springs are really allowing full return then it is internal, but this is definitely the issue. Good Luck, it can be fixed without changing vendors.
 
Finally getting back to this. The hydrolic problem appears to be in my passenger side right master cylinder. But it's weird. When the brake is sticking, I can manually pull on the pedal back out and it doesn't budge and no change. But if I pump the brake a few times, the pressure will release and the brake frees.

And today I went to drain the fluid from the right side. I opened the bleeder valve and pumped some air down through the reservoir. Nothing came out. I went into the airplane and pumped the right brake a few times. I heard fluid squirting out the bleeder valve into my container. I went back out and pumped air again and all the fluid drained.

It seems like the MC plugs up if it sits for a long time. Pump it once or twice and it opens to the reservoir. Should I just replace the MC? Or does this symptom point to something other than the MC?
 
There should be a small amount of ?slop? when you release the peddle by pulling it back. If there isn?t, I could see a scenario of it being right on the ragged edge where the internal seal isn?t opening up the port unless you mess with it a bit. If that is the case, check the clevis/jamb nut adjustment and make sure the peddle was fabricated correctly and the throw allows for that slop. If it?s tight, there is a problem with the setup, not the MC.
If the slop is there, my guess is there is some kind of weird damage to the seal that could be fixed by rebuilding.
Just a guess.
 
Apparent resolution

In the end I replaced the calliper and brake-plate and pads. Turns out the calliper was badly warped. I also rebuilt the passenger side master cylinder. There was nothing obvious I could see wrong with the MC. I got it all back together today and went for a little flight.

All appears to be working correctly.

As always, I appreciate very much the input and advice and shared experiences offered on this forum.
 
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