blocked brakes

[Juliet Golf]

This afternoon, after an uneventful flight and landing, I noticed the plane was turning to the left. I guessed the brakes were still active on the left wheel so I brake again to move the piston and try to release the pressure. Instead, no release, the brakes are stuck on. We had to purge the lines to manage to partly release the pressure. The right wheel was still breaking hard; although we manage to pull the plane off of the taxiway.

stuck parking brake? I didn't touch it since the holding point before takeoff...

Stuck lever? purging the lines would release the pressure..

Stuck piston? why it was turning LEFT, and after blocking both wheels, and purging the lines, the right wheel was still with significant brake friction...

 

any idea?

[Jim]

Matco or OEM brakes?

[ralarcon]

This afternoon, after an uneventful flight and landing, I noticed the plane was turning to the left. I guessed the brakes were still active on the left wheel so I brake again to move the piston and try to release the pressure. Instead, no release, the brakes are stuck on. We had to purge the lines to manage to partly release the pressure. The right wheel was still breaking hard; although we manage to pull the plane off of the taxiway.

stuck parking brake? I didn't touch it since the holding point before takeoff...

Stuck lever? purging the lines would release the pressure..

Stuck piston? why it was turning LEFT, and after blocking both wheels, and purging the lines, the right wheel was still with significant brake friction...

 

any idea?

Had the same thing happen to me with my OEM brakes. Replaced Master cylinder, and brakes (MATCO) , no more issues.

 

Cheers

[FastEddieB]

On my Sky Arrow with Marc Ignegno brakes, the dragging was caused by some corrosion/grunge in the brake cylinder bore.

 

Cleaned up with some polishing compound and has worked fine since.

 

I have some photos if that would help.

[FastEddieB]

Before:

 

 

After:

 

 

You can see some minor pitting remained, but there's no leakage or binding now - so far, so good.

 

BTW, the plane is hangared and has only spent a handful of nights out in weather.

[Anticept]

Coat that surface with hydraulic fluid before you put it back together and you'll be good.

 

I don't think there's a grease that you can use on a hydraulic cylinder wall, nor would I really want it that close to the piston surface, but if anyone knows of one, chime in.

[Juliet Golf]

Thanks for your replies and photos; i'll unmount all this week end and see what's happening there.

[ctfarmer]

My Matco brake on the RHS did the same thing last week.

 

 Mine is a CTLS with a total time of 26Hrs. Pads are as new.

 

The pads for some reason on the RHS would jam and not slide along the pins/bolts so the brake pressure would not release. I could not wheel it out of the hangar it was jammed so solidly.

 

After working the pads back and forth, levering gently apart, tapping the caliper with a soft hammer and application of light oil to lubricate the guides applying with a feeler gauge between the pad and the piston, they are now fine but it is surprising how such an issue could occur at all let alone at such low hours.

 

cheers peter

[FastEddieB]

JG,

 

I don't think you ever answered concerning your brake brand.

 

On my Marc Ignegnos, I make it a monthly routine to clean and lightly lube (with disc brake lubricant on a Q-tip) the pins that the rotors are supposed to float on. If those don't float easily, that can also lead to binding.

 

Sounds like Matcos float their calipers, not their rotors, so that would apply to the caliper pins instead. Just be careful with regular oil in that area - it can get very hot and migrate to the pads, which is obviously not good. Hence the dedicated disc brake lube, available in tiny packs for a couple dollars at any auto parts store.

 

[Ian]

We had a similar experience a couple of months back - taxying out and one wheel virtually locked up - managed to free it enough to be able to take off and get back to our home airfield - it looked as though it was just worn pads so got another set ordered (Matco) - I was then away in France so left my trusty co-pilot & mechanic to do the work - here is the email he sent me:

 

The initial problem (brake jammed on) looked to be worn out pads, mainly deduced because I’d looked at the caliper assembly and seen In my opinion a slightly excessive gap between, caliper, disc and pads and the pads looked thinish.

 

Going back to the actual problem we’d had, the single piston (a sliding caliper) had travelled so far out of the caliper that it had become ‘cock-eyed’ and jammed (Halfpenny Green), again the only logical explanation is worn pads but It didn’t explain how the piston could come out so far, I’d put that down as bad design or lack of synergy between the components assembled to be CTLS brakes, a possibility.

 

Anyhow, new pads in hand and now equipped with tools I set about sorting out the problem, the good news, the pads are the correct ones, the bad news……  we don’t need them, why?

 

Well on closer examination the caliper (single piston sliding type) works exactly the same as an automotive one, the only real difference is its actual construction, a lot of the casting and ‘mass’ of the caliper on an automotive version is not applied to these much lighter aviation ones, where I’m going with this is that the slide and pad retention mechanism is condensed into two 6mm bolts.  So the rigidity and security of these bolts is important and the brake function doesn’t work to well when they are loose, yes I’ll say that again, the bolts that hold the caliper together were loose, the starboards side by about 2 ½ threads each and the port side by 1 ½ turns….

 

So there’s the answer, that’s why the piston jammed, the caliper was opening up like a clam in reverse allowing excessive piston travel and very nearly allowing it to pop out (going cock-eyed), I tightened all four bolts, had a general look around, checked the operation with a few hefty pulls and all is well.  The brake also feels positive now (rigidity restored!) so all is well, the pads in the aircraft are probably 50% worn at the moment so we’re fine for a good while.

 

I’d say in automotive world that could not happen as the ‘clam’ section that slides and holds the pads is usually a substantial casting where the CTLS version is a sort of Meccano setup, that’s absolutely fine but the bolts need to be tight.

[Anticept]

We tend to call the brake systems where the caliper moves "floating calipers" or "cleveland brakes". Marc Ingegno brakes are "floating rotor".

[paul m]

Common cause.

Most of the time it is caused by pad wear and the piston comes too far out and gets cocked slightly. Usually replacing the brake pads works just fine.

That said once in a while water or dirt intrusion can cause some sticking. That requires removing the caliper and then the piston. Cleaning or buffing up the surface and "O" ring replacement.

Hi Roger,

Had both brakes lock up after run up recently. Looks like problem is this one--worn pads, piston won't retract. Can you tell me which brake pads I need to order from Matco? 140 total hours on them. I do usually have long taxi runs at my home airport.

[Anticept]

WHLBRL-1 BRAKE RELINE KIT: http://www.matcomfg.com/BRAKERELINEKIT-idv-3485-12.html

 

Just so you know, the liners are cleveland compatible Rapco RA066-10600 (old rapco pn RA66-106), Matco part M66-106. You also need 3 MSC4-6 rivets and 3 MSC4-4 rivets per set of 2 liners. The reline kit above already comes with all of this; that was just extra informational stuff if anyone wanted to know.

 

You need the tool too, found here: http://www.aircraftspruce.com/catalog/topages/RapcoBrake.php?clickkey=62352

 

Here's the instructions for the tool: http://www.rapcoinc.com/pdf/Informational%20Tips/Rivet%20Tool%20Instructions.pdf

 

Also, I personally strongly recommend that you do NOT just punch out the rivet. The matco pads (the actual pads, not the liners) can be deformed that way. Use a #31 or 1/8th inch bit to drill and pull off the shop head of the rivet before punching. If you're good you can use a #30 bit, which is equal to the diameter of the rivet and makes it a little easier, but you need to know when to stop.

[paul m]

Thank you Corey. Can you clarify something? Roger referred to the pads being worn. Are the pads and liners two different things? Would one ever need to replace the pads?

[Anticept]

Pads are actually the metal backing (also known as the shoe). Liners are the friction material.

[FastEddieB]

Pads are actually the metal backing (also known as the shoe). Liners are the friction material.

Don't know that this may not technically be correct (and it appears to be - thanks, I did not know that), but in common usage when someone refers to the pads being worn they are generally referring to the linings.

[Anticept]

It is historically technically correct. Common usage is incorrect. These days I'd say the "technical" term should be updated.

 

I've also seen the complete assembly referred to as the pads or shoes.

[FastEddieB]

I've apparently been using the wrong terminology for about 50 years.

 

As in, "I let my pads wear down to the backing plates and it scored my rotors".

 

Learn something every day!

[gbigs]

Common cause.

 

Most of the time it is caused by pad wear and the piston comes too far out and gets cocked slightly. Usually replacing the brake pads works just fine.

 

That said once in a while water or dirt intrusion can cause some sticking. That requires removing the caliper and then the piston. Cleaning or buffing up the surface and "O" ring replacement.

 

Both locked on touchdown with 'new' pads as delivered from the factory.  Replaced them with better pads and it never happened again.

[FlyingMonkey]

I just had my wheels off to replace the tires, I did the pads at that time.  The old pads probably had 40% left, but like you say pads are cheap and now I won't have to worry about it for the rest of the year.

 

Done the locked brake routine, not going there again.

[Doug G.]

Since I am dealing only with my own plane I use Matco's relining service. It is fairly inexpensive and I always have a spare set on hand, or I can wait and send the spare set when the others get close.

I also had a situation where the guide pins were out of alignment which caused brake drag (not lockup). They are not centered on the bolt end so they must be adjusted to allow free float. One of mine loosened and caused the binding. A couple calls to Matco diagnosed the problem.

[FlyingMonkey]

Marco specifically says not to lube the guides.

[Doug G.]

You should lube the caliper guide pins. I clean with CRC carb spray cleaner and then use a smidgen (Arkansas term ) of the synthetic Mobile One grease on them. Lets those pins move without binding.

Matco would prefer you don't use any grease. I specifically asked. I suppose it accumulates dirt.

[Doug G.]

Probably looking at a toss up since the dirt will cause more wear, but water will cause corrosion. I asked about brake grease made for higher temps, but they did not recommend it.

[Tom Baker]

MFG"s are always right. Why do you think there are so many LOA's in the LSA market and FAA required fixes for other aircraft over the many years.

I think Matco worries about grease getting to the pads. Just use a thin film. They may even be worried about dirt accumulation, but that happens any way. Metal on metal there doesn't move as smooth dry and no grease allows more water oxidation and corrosion. Its served me well for 10 years and on many planes.

 

They may not be always right, but they are more often than not.

 

I have been working on airplanes for 35 years, I know I'm a young pup. I have seen where the application of lubricant has transferred the wear from the sacrificial part to the part they intended to last. This happens over a longer period of time than 10 years and a thousand or so hours.

 

I have replaced brake assemblies on older aircraft because of this, but the most notable was a set of control wheel shafts.

 

The owner decided to lube the control shafts with silicone grease, instead of a simple cleaning every once in a while. The grease made them move really smooth. When I replaced them they had worn almost all the way though the 1/8" wall thickness of the shaft. I replaced the bushing that the shaft slid through at the same time I replaced the shaft. The bushing which is supposed to wear had almost no wear, where the shaft had worn to the point it was no longer serviceable. In this case the grease caused two $1,000 parts to be worn out instead of the $20 bushing.

 

Once the grease was applied the first time there was no going back, at least not without major disassembly. Because of this the grease was continually applied until the shafts were replaced.