Brake sticks when hot

jwilbur · #1 03-03-2020, 06:48 AM

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.

lr172 · #2 03-03-2020, 07:20 AM

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

airguy · #3 03-03-2020, 07:54 AM

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.

lr172 · #4 03-03-2020, 08:14 AM

Quote:

Originally Posted by airguy

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

Avengerboss · #5 03-03-2020, 08:27 AM

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.

jwilbur · #6 03-03-2020, 08:31 AM

Quote:

Originally Posted by lr172

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.

Ralph Inkster · #7 03-03-2020, 08:34 AM

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.

9GT · #8 03-03-2020, 03:09 PM

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.

OKAV8r · #9 03-03-2020, 03:23 PM

Check the torque of the caliper bolts. If they are over tightened, the caliper casting can warp, and possibly be a source of binding.

rleffler · #10 03-04-2020, 04:19 AM

Quote:

Originally Posted by jwilbur

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.