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Matco brake caliper piston leaking?

Draker

Well Known Member
Did my very first condition inspection about a week ago, and replaced the brake pads. Not that they needed replacing, but I wanted to make sure I knew how to do the job. Two weeks later, I see a very small little drip of brake fluid under the left caliper. Pull the caliper and the inboard pad (the one the caliper piston pushes on) is soaked with brake fluid. Are these things supposed to leak? From the Matco drawing it looks like there's an O-ring in there. Are these expected to leak this new?
 
The "O" ring is fully replaceable! The reason for a leak can be things like age deterioration, or trash getting between/under the "O" ring.

Disassemble, clean, reassemble with new ring and bleed that side of the system.
 
Reassembly

Just be sure to put the o-ring side of the puck in first.

IMG_9979.jpeg
 
Ryan,

I have a couple of the original Vans supplied o-rings that I replaced with Vitron o-rings. You are welcome to them if you want them.
 
The "O" ring is fully replaceable! The reason for a leak can be things like age deterioration, or trash getting between/under the "O" ring.

Disassemble, clean, reassemble with new ring and bleed that side of the system.

Thanks! I don't suppose I can easily cap off the brake line and retain the fluid. It's all gonna pour right out once the piston is removed.

My experience is they do if over heated, taxiing with too high of throttle.

I am definitely riding the brakes while taxiing. Even at idle, the airplane really moves and I'm not used to taxiing this fast!

Also consider upgrading to Viton o-rings for higher temps. See Vans notice for details:

Wish I would have seen this one before my inspection! Thanks for the link. Surprisingly Spruce doesn't seem to have the Viton ones in my size -222. Looks like I'll need to order directly from Vans.

I have a couple of the original Vans supplied o-rings that I replaced with Vitron o-rings. You are welcome to them if you want them.

Thanks. So far it's a very small drip and won't stop me from flying, so I can wait a week or so for the new Viton ones to ship.
 
Thanks! I don't suppose I can easily cap off the brake line and retain the fluid. It's all gonna pour right out once the piston is removed.

I am definitely riding the brakes while taxiing. Even at idle, the airplane really moves and I'm not used to taxiing this fast!

Thanks. So far it's a very small drip and won't stop me from flying, so I can wait a week or so for the new Viton ones to ship.

Yes, you can plug off the line (as soon as you remove it from the caliper) and place some fluid in the cylinder before you install the piston. Have a cap on it too. Have the cap loose as you push the piston all the way in to remove the air... fluid will escape when the air is gone, then close the cap. Install the caliper and remove the caliper cap.... nothing will drip out. Uncap the line, it will start dripping because it is vented from above. Install the line as it is dripping (no air=good) and tighten.

SLOWLY push on the pedal for that side with your hand. It will have a long travel the first few times. Retract it slowly and repeat till the pedal is firm.. Only a couple are needed. If not firm, then bleed it. I have never had to yet.

Make sure your reservoir is properly filled before and after you do this.

Riding the brakes....Set your idle rpm just above shaking. It is easy to control idle rpm with throttle, but you need to be able to get it down to 4-500 if you want to land it short. It will also really help in taxi speed. With any metal prop, you will need to add throttle if you are set at 4-500 rpm and then just tap brakes for directional control and apply brakes to slow taxi speed down... give them a firm poke and get off of them.
Do not ride the brakes.

Spruce has the cap and plug that will fit your line and caliper.

You can also clean the wet pad with Breakleen. and let it dry out well. I have had good luck with this also. But, you wanted the experience, so install a new pad for good insurance.
 
Set your idle rpm just above shaking. It is easy to control idle rpm with throttle, but you need to be able to get it down to 4-500 if you want to land it short. It will also really help in taxi speed. With any metal prop, you will need to add throttle if you are set at 4-500 rpm and then just tap brakes for directional control and apply brakes to slow taxi speed down... give them a firm poke and get off of them.
Do not ride the brakes.

+1 on the idle - it will help your landings too. (ask me how I know :eek:) Set idle for hot operation. Even if it is a little low when cold, you can always move up the throttle.
 
Given the problem occurring right after the maintenance, I would first precisely determine the leak source. Given the timing, I would think that a crack in the flare area of the tube is more likely than the oring, unless all off the hard braking was done between the pad change and appearance of fluid, then I would concur with others that the oring is more likely.
 
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Reassembly tips

Are you still using the stock Nitrile rubber O-rings in your calipers? If so, upgrade to the more heat resistant Viton O-rings.


See these two threads for tips when reassembling your calipers.

https://vansairforce.net/community/showthread.php?t=206981&highlight=brake

Last photo in 2nd last post on page linked below.

https://vansairforce.net/community/showthread.php?t=10366&page=2&highlight=brakes

I almost forgot. Be sure to remove all that hydraulic oil from your new inner brake pad. Spray it with aerosol brake parts cleaner. This is available at any auto parts store. Don't buy the "EPA friendly" stuff. It's worthless. Spray and let dry. It will evaporate and take the hydraulic fluid with it. Repeat as needed. The high temp brake grease is also available at your local auto parts store and on Amazon.

Charlie
 
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A small drip can turn into no grip and end up in a rip into the bushes.
I would never drive/fly with any drip in the brake fluid area.
I just fixed this problem 6 weeks ago on my RV-6A.
And yes I had just been inspecting everything and had the pants off and had closed up and was going to go flying.
Picking up that errant piece of trash under the plane when WHAT THE ^(^**& is that spot of water doing under my wheel???
Not water. Brake fluid.
Well no flying that day.
I fixed pronto.
I like to stop when I need to.
Drove a 40,000 pound truck with a dozer on the back out into a field once because of not enough brakes.
I like good brakes not bad breaks.
Art
 
I replaced the o rings with Viton rings from Vans and it corrected both the fluid leak AND a persistent groaning noise when braking at low speeds. No more braking problems! Good upgrade.
 
Piston Leaking

I replaced my caliper O rings with Viton -222 a long time ago, right after the first long hot taxi with riding brakes, to the discovery of puddles under the mains. Heat flattens the Buna N rings. If you'd like to get 25 of them for $20, go to McMasterCarr, which should be on your browser tabs already if you are a real builder! Part number 9464K64 for the 75 durometer rings. They are good to +400 F.

Now, if you want to venture into a more controversial area, I changed to Silicone brake fluid many years ago also, as it is good to +500 F, and doesn't turn into a sticky mess over time like the standard MIL spec fluid. And is much less expensive. A good 10 years and I have had absolutely no problems.
 
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