Matco disk brake getting hot

[danny_galaga]

I figured the engine section is the best place to ask 

 

My plane has matco ph-8 disk brakes. The right one is getting much hotter than the left one. Have to add extra herbs after landing to taxi. And much harder to push back into the hangar. It looked a bit glazed, so I was hoping maybe it's suffering from a positive feedback loop whereby the more it overheats, the more glazed it becomes. The more glazed the hotter it gets. I took the caliper off, and de glazed with wet and dry and water. Also touched up the pads with wet and dry on a flat surface. The system is comically simple, and everything thing seems to moving. Pressing the brake pedal gently showed the piston moving. The caliper sliding thing slides. I'm at a loss! If I don't hear of any easier things to try by tomorrow, I'll swap left caliper for right (they are symmetrical) and see if the problem follows it.

[skippydiesel]

Speculation:

 

A brake gets hot due to friction. Friction, in this context, is when two materials/surfaces moving at diffrent speeds make contact.

Two identical (?) brake systems should deliver the same temperature IF the same forces are applied. Is this an independent brake system (as in castering tail /nose wheel) or a single acting Master Cylinder system?

Glazing is more likly to result in cooler(less effective) brakes as the smooth surface of the glazed disk results in less friction.

Difference's in materials (brake pad/disk) are likly to result in diffrent temperatures. Differences' can be caused by contamination.  Oil is a common one, but other substances eg metal filings can have a similar effect. Do you wash your brakes? If so could detergent residue be contaminating the surfaces?

Misalignment of calliper 

Incorrectly assembled or manufacturing defect, may cause the slave cylinder piston to not retract, causing the brake pad to rub/bind at all times, generating some heat that just increases with braking effort

Air in one brake line/system

😈

 

[skippydiesel]

Just another , random. thought - Are you using the correct brake fluid for your system?😈

[BrendAn]

48 minutes ago, danny_galaga said:

I figured the engine section is the best place to ask 

 

My plane has matco ph-8 disk brakes. The right one is getting much hotter than the left one. Have to add extra herbs after landing to taxi. And much harder to push back into the hangar. It looked a bit glazed, so I was hoping maybe it's suffering from a positive feedback loop whereby the more it overheats, the more glazed it becomes. The more glazed the hotter it gets. I took the caliper off, and de glazed with wet and dry and water. Also touched up the pads with wet and dry on a flat surface. The system is comically simple, and everything thing seems to moving. Pressing the brake pedal gently showed the piston moving. The caliper sliding thing slides. I'm at a loss! If I don't hear of any easier things to try by tomorrow, I'll swap left caliper for right (they are symmetrical) and see if the problem follows it.

I think you will find a tight piston.

 . Can you push the piston In by hand 

[Blueadventures]

1 hour ago, danny_galaga said:

I figured the engine section is the best place to ask 

 

My plane has matco ph-8 disk brakes. The right one is getting much hotter than the left one. Have to add extra herbs after landing to taxi. And much harder to push back into the hangar. It looked a bit glazed, so I was hoping maybe it's suffering from a positive feedback loop whereby the more it overheats, the more glazed it becomes. The more glazed the hotter it gets. I took the caliper off, and de glazed with wet and dry and water. Also touched up the pads with wet and dry on a flat surface. The system is comically simple, and everything thing seems to moving. Pressing the brake pedal gently showed the piston moving. The caliper sliding thing slides. I'm at a loss! If I don't hear of any easier things to try by tomorrow, I'll swap left caliper for right (they are symmetrical) and see if the problem follows it.

Is the piston returning (coming off, the pad retracting off the disk surface); if not that cause heat.

[kgwilson]

I agree with Brendan. I reckon the piston is not returning after braking. Pull the whole wheel cylinder apart & check for rub marks grit etc, clean everything meticulously,  reassemble & make sure moving parts i.e. the piston moves freely.

[BrendAn]

When you own Honda road bikes you learn about sticky brake pistons

[Thruster88]

My friend once had a similar problem in his Socata TB10 Tobago. Problem turned out to be the master cylinder was not able to fully retract so hydraulic pressure could not be released to the reservoir. The hotter it got the harder the brake grabbed. 

 

Do you have a park brake valve or anything that might be holding pressure. Wrong fluid and swollen orings? 

Edited Monday at 07:50 AM by Thruster88

[facthunter]

I'm with Thruster. Check residual pressure in the specific brake line.  Crack the Bleed. That master cyl may not be porting. Check there's some free play before the Piston moves. Your pads may be too thick also. Nev

[danny_galaga]

Some good thoughts there.

 

I forgot to mention that since I'm on a grass field the only time I use the brakes is PARK on start and engine run ups, and to 'unkink' the tailwheel after pulling the plane backwards out of the hangar. And then of course a quick jab when taxiing to check the brakes are working. 

 

I'm 

Edited Monday at 09:36 AM by danny_galaga

[danny_galaga]

4 hours ago, skippydiesel said:

Just another , random. thought - Are you using the correct brake fluid for your system?😈

Definitely the correct fluid. It's a mineral oil system. Just using what's recommended. My experience with hydraulic brakes in cars is that if you have air in the system, the reverse of what you are implying happens. Ask me how I know 😂 

[danny_galaga]

Today I'll do some taxi trials before pulling out the tools. 

 

Normal taxi, to establish how quickly it gets hot. Ill do that near the hangar, once I know how quickly it gets hot, it saves me taxiing a long way. I suspect it won't take much. I have one of those thermometers you point at with.

Between each test, cool the brakes down.

 

Next, start up with park brakes off but brakes applied. Taxi.

 

Then start up no brakes and no park brakes (by now the engine will start straight into an idle so it'll be safe as long as I'm ready to act). Taxi.

 

Then start up from.passenger seat, using the brakes. Taxi. One of you mentioned it could be a master cylinder, these tests will definitely sniff that out, or whether it's the park brakes. 

[Blueadventures]

You could just jack wheel off ground and spin wheel by hand then apply brake and see if it stops then release brake pressure and see if wheel can spin; do same to other wheel. This will confirm if the caliper piston is retract Ing.  Be a good start. Have fun and solve the issue. Cheers.

[BrendAn]

Unless the master cylinders are not fitted correctly I would be surprised if it's not a sticky caliper piston.

Do as blue says and crack the bleed nipple to rule out hyd pressure. If it's still tight it's the piston 

[Geoff_H]

Can be deterioration of O ring.  Make sure that you are using correct fluid and O ring is correct type.  If O ring gets wrong fluid rubber will expand and restrict piston movement.   Just a thought. 

[skippydiesel]

14 hours ago, danny_galaga said:

Definitely the correct fluid. It's a mineral oil system. Just using what's recommended. My experience with hydraulic brakes in cars is that if you have air in the system, the reverse of what you are implying happens. Ask me how I know 😂 

It sounds like a split/independent brake system (like mine) - Air bubbles in one side will tend to give uneven brake pressure. The "good" side taking most of the braking loads, getting hotter. The only similarity with a car brake system is the hydraulic theory - its has more in common  tractor system (independent brakes)😈

[skippydiesel]

Years ago I helped a pilot friend diagnose/fix his brake problem that had lived with  for years. Turned out his mechanic had assembled the callipers with the rubber buckets in the wrong orientation. Easy done, easy fix😈

[facthunter]

Air in a system gives a soft pedal.. Taxying in a crosswind will make one side do all the work Nev

[danny_galaga]

53 minutes ago, skippydiesel said:

It sounds like a split/independent brake system (like mine) - Air bubbles in one side will tend to give uneven brake pressure. The "good" side taking most of the braking loads, getting hotter. The only similarity with a car brake system is the hydraulic theory - its has more in common  tractor system (independent brakes)😈

I got all scientific n shit this morning and did lots of taxiing. Except for one anomaly (it's not science if there isn't a mysterious outlier 😄 ) I very quickly worked out that the park brake was the issue. 

 

So I did some (very inconsistent) circuits. Not using the park brake. When I came back the left was even hotter than I had measured the right! WTF? 

 

But now I see what you're saying. The only problem is that everything starts off free, and since I'm not even using the brakes you would think it would stay that way. Nonetheless, it can't hurt to bleed the brakes and see if something changes.

 

Oh, a tecnam landed at the same time so I had a chance to measure their brake temps to get an idea of what it normally be 

Edited Tuesday at 01:00 AM by danny_galaga

[Blueadventures]

28 minutes ago, danny_galaga said:

I got all scientific n shit this morning and did lots of taxiing. Except for one anomaly (it's not science if there isn't a mysterious outlier 😄 ) I very quickly worked out that the park brake was the issue. 

 

So I did some (very inconsistent) circuits. Not using the park brake. When I came back the left was even hotter than I had measured the right! WTF? 

 

But now I see what you're saying. The only problem is that everything starts off free, and since I'm not even using the brakes you would think it would stay that way. Nonetheless, it can't hurt to bleed the brakes and see if something changes.

 

Oh, a tecnam landed at the same time so I had a chance to measure their brake temps to get an idea of what it normally be 

Have you tried pulling each leg forward and noting the ease / resistance of wheels turning after your taxiing?  You're getting friction somehow.   Even worth trying the same with park brake applied. 

Edited Tuesday at 01:28 AM by Blueadventures

[facthunter]

There's no spring pushing a pad Off a disc. Some drag is always there as any clearance will make the Pedal go further down. Loose or failed wheel bearing will cause this, too.  I don't like Hydraulic PARK brakes. They can't be relied on. (To free up OR hold on.).  Nev

[danny_galaga]

8 hours ago, Blueadventures said:

Have you tried pulling each leg forward and noting the ease / resistance of wheels turning after your taxiing?  You're getting friction somehow.   Even worth trying the same with park brake applied. 

Yes, that's how I realised in the first place. Furthermore, when cooled down, the wheels turn easily again. Anyway, I've done something to them before I went home. Will test it tomorrow and report back 🙂

[danny_galaga]

solved! I think 😄

 

Another pilot in the hangar asked what the grease on the sliding pins on the caliper looked like. But when I took the right one off a few days ago it was clean as a whistle and I just assumed that's how they are. But I shouldn't be surprised with this kit. He said any similar brakes he's ever worked on always had a thin smear of grease. I happened to have some anti seize grease which seems ideal for this job. Did both calipers. Two landings and a taxi back to the hangar gave me a much more respectable 35 ish degrees, both brakes with ambient of about 18°

 

Will try the park brake tomorrow. I wanted to keep potential multiple issues separate.

[skippydiesel]

Grease & brakes are not usually compatible - always a first time.

 

If going down the slipy track, I suggest using a high temperature lubricant, like graphite, rather than an oil based lubricant.😈

[BrendAn]

1 hour ago, danny_galaga said:

solved! I think 😄

 

Another pilot in the hangar asked what the grease on the sliding pins on the caliper looked like. But when I took the right one off a few days ago it was clean as a whistle and I just assumed that's how they are. But I shouldn't be surprised with this kit. He said any similar brakes he's ever worked on always had a thin smear of grease. I happened to have some anti seize grease which seems ideal for this job. Did both calipers. Two landings and a taxi back to the hangar gave me a much more respectable 35 ish degrees, both brakes with ambient of about 18°

 

Will try the park brake tomorrow. I wanted to keep potential multiple issues separate.

you threw us off at the start when u said the calipers were sliding ok.  antisieze is fine. it has a high temp tolerance .