New M20J owner -- brakes and maintenance options for San Diego

[BaldEagle]

Hi all,

Thought I'd post a quick intro.  I recently started getting back into flying after a 12-year hiatus and took delivery of a '78 M20J yesterday.  Insurance wanted a checkout so I did that yesterday.  After landing I noticed it required a ridiculous amount of pressure on the toe brakes to bring the thing to a stop.  It didn't need all that much toe pressure when doing the run-ups though.  I've not looked at the condition of the pads and discs yet, but if they're okay should I get the brake system bled?  Master brake cylinder was apparently replaced fairly recently but I can't find reference to that in the logs.  I do see an entry showing that the brakes were last bled a little over 2 years ago, and after doing some cursory research on this forum someone did recommend that they should be bled every 2 or 3 years.  The aircraft has toe brakes on co-pilot side if that is relevant.  The ferry pilot also reported that the left toe brake was a bit more spongy that the right (I didn't notice) and suspected it could be air in the system.

So with all that in mind, any recommendations for an A&P at KSEE...?  I'm familiar with Crownair but someone who's familiar with Mooneys located on the field would be desirable.

[N201MKTurbo]

If the master cylinder was replaced than they would need to be bled. If they aren't spongy, they may need to be conditioned. Condition them by making a couple of runs down the runway or taxiway with moderate power and braking. 

http://aeromech-inc.com/brakeliningconditioningprocedures.htm

[jonhop]

I'm based at KSEE and just lost my independent A&P... I know how to bleed them though and could help, as I think that falls into Pilot performed maintenance. I've had to bleed my breaks each time I've had the wheels off for tire replacement and wheel bearing grease repacks during annuals. 

[jetdriven]

The 5606 hydraulic fluid gets syrupy after a few years too. You may try bleeding them two different ways. Top down, like a car,,,pump the brakes and hold, the helper opens the bleeder screw and bleeds down, then tighten the bleeder, then repeat. Also, try pumping the copilot side MC's as well as the pilot side. DO NOT let the reservoir run dry, you will be in for hell after that.

The other way is a pressure pot or a squirt can from the bleeder bottom up.  Watch for reservoir overfilling.

check condition of pads and rotors as well. When the pads get thin, the piston comes further out of the bore of the brake cylinder. Frequently there is corrosion and pitting in that area and then the O-ring on the brake cylinder starts to leak through this rough surface.

of course, follow the SMM and work under supervision of an A&P to keep it legal and safe.

Edited March 7, 2018 by jetdriven

[kortopates]

I'm based at KSEE and just lost my independent A&P... I know how to bleed them though and could help, as I think that falls into Pilot performed maintenance. I've had to bleed my breaks each time I've had the wheels off for tire replacement and wheel bearing grease repacks during annuals. 

Actually it doesn’t fall under PM, only adding fluid:
43.A
(8) Replenishing hydraulic fluid in the hydraulic reservoir



Sent from my iPhone using Tapatalk

[Joe Larussa]

I've found that our brakes just aren't the best. 

[EricJ]

5 minutes ago, Joe Larussa said:

I've found that our brakes just aren't the best. 

I was hoping it was just me, but my brakes suck.   The rotors look like they're in good shape, there's plenty of pad material, just not much braking torque to speak of.   The brakes will hold it in place decently if it's not moving, up to nearly full power, but stopping torque is more or less inadequate.   Are there multiple brands with different pad compounds available?    I'm guessing the pads that are in there were compounded for longevity rather than torque.     If they were automobile pads I'd say they were a duration-oriented cheap street pad, and I'd like a mild autocross or performance pad that actually makes some torque.

[N201MKTurbo]

You should strive to land where you don't  need brakes at all. Your brake and tire dollar will go a long ways further.

Brakes are just for stopping at the tie down. 

[kortopates]

40 minutes ago, EricJ said:

I was hoping it was just me, but my brakes suck.   The rotors look like they're in good shape, there's plenty of pad material, just not much braking torque to speak of.   The brakes will hold it in place decently if it's not moving, up to nearly full power, but stopping torque is more or less inadequate.   Are there multiple brands with different pad compounds available?    I'm guessing the pads that are in there were compounded for longevity rather than torque.     If they were automobile pads I'd say they were a duration-oriented cheap street pad, and I'd like a mild autocross or performance pad that actually makes some torque.

All other things being normal, your brake pad longevity is probably proportional to the max gross weight limit of your aircraft; assuming you operate it up to its max on occasion. But all `things are never equal and sometimes we can get great pad longevity by not using the brakes and just coasting to an easy to make turn off on landing.

Its interesting as the Mooney's went above 2900 lbs max gross weight Mooney found they really needed to go to double puck brakes which doubles the pads per brake to get better longevity. Many of the earlier Bravo's that initially were fitted with the same J & K brakes where retrofitted with dual puck brakes used now on the longbody's. By the time time the M20K Encore came out with its increased max gross weight it too was fitted with double puck brakes. All of the 252's are eligible for the brake retrofit, but I am not sure about anything earlier. 

But a couple of things to consider that could be at play preventing your bird from getting full braking action. Make sure whenever you change the pads that you measure the disk thickness to make sure its still within limits. Our aircraft disks aren't like automotive disk with lots of extra thickness since that would make them heavier than necessary. They have very little extra to stay light and need periodic replacement. Secondly, when you do replace brake pads, be sure to "condition" them before returning the plane to normal service. Or after your A&P or shop replaces them for you, be sure to follow the conditioning procedure on how to effectively brake in the brake pads to provide you with optimal braking. They could otherwise get glazed and provide somewhat diminished braking action from the very beginning if they get too heated before braking them in. The Mooney MM discusses how to condition the pads as do the manufacturer of the pads.   

Edited March 8, 2018 by kortopates

[EricJ]

2 minutes ago, kortopates said:

All other things being normal, your brake pad longevity is probably proportional to the max gross weight limit of your aircraft; assuming you operate it up to its max on occasion. But all `things are never equal and sometimes we can get great pad longevity by not using the brakes and just coasting to an easy to make turn off on landing. Its interesting as the Mooney's went above 2900 lbs max gross weight Mooney found they really needed to go to double puck brakes which doubles the pads per brake to get better longevity. Many of the earlier Bravo's that initially were fitted with the same J & K brakes where retrofitted with dual puck brakes used now on the longbody's by the time time the M20K Encore came out with its increased max gross weight it too was fitted with double puck brakes. All of the 252's are eligible for the brake retrofit, but I am not sure about anything earlier. 

But a couple of things to consider that could be at play preventing your bird from getting full braking action. Make sure whenever you change the pads that you measure the disk thickness to make sure its still within limits. Our aircraft disks aren't like automotive disk with lots of extra thickness since that would make them heavier than necessary. They have very little extra to stay light and need periodic replacement. Secondly, when you do replace brake pads, be sure to "condition" them before returning the plane to normal service. Or after your A&P or shop replaces them for you, be sure to follow the conditioning procedure on how to effectively brake in the brake pads to provide you with optimal braking. They could otherwise get glazed and provide somewhat diminished braking action from the very beginning if they get too heated before braking them in. The Mooney MM discusses how to condition the pads as do the manufacturer of the pads.   

A normal tradeoff on brake pad material is longevity vs braking torque.   For cars, street pads are made to last a long time, not create too much dust or noise, and still give decent braking torque over moderate temperature ranges.    Race pads often make dust like crazy, squeal like mad (which is why they're fun to drive on the street), and don't last as long but make much greater braking torque over a much broader temperature range.   So getting good braking torque (or exceptional longevity) has a lot to do with the pad material, so I'm wondering what's available or whether there is any variation in compounds for typical Mooney brake pads.

Even on many race cars the rear brake rotors aren't ventilated, so they're similar to the thin rotors on an airplane.   It's common to use aggressive race pads on those, too.   They hold up decently doing a lot more work than the occasional single stop from 60-70 mph or so that a light airplane needs.   I think the rotors on the airplane will hold up to a lot more than what they're currently doing on mine, since they don't really need to do much relatively speaking.

My pedals are firm, so I think the fluid is fine and there's no air in the lines, and they're smooth and consistent so it seems like the rotors are fine.   There's just not a lot of torque.   On a race car the first go-to change for that situation would be moving to a more aggressive pad material.    "Conditioning" brakes to transfer pad material into the rotor face in a race application is called "bedding in", since racers are less family friendly, I suppose. 

I suspect that light aircraft pads are not made for high temperatures, which suggests the pads may be subject to glazing if they got overheated sometime in their life.   My annual inspection is due in May, so maybe we'll pop the pads out at that time and see if they've just gotten too hot somewhere along the way and glazed.    That'd be an easy fix.

And to Jim's point, going into short fields on occasion, or having to land long for whatever reason, it's always good to have useful brakes for when you need them.   Not having them when you could really make use of them is annoying at best and potentially expensive or dangerous at worst.    If there's a means to make them better, like other similar aircraft I've flown, I'm interested in figuring that out.

 

[ArtVandelay]

Brake linings are $12.75 at spruce, I would not make any special effort to save them.

[kortopates]

16 minutes ago, EricJ said:

A normal tradeoff on brake pad material is longevity vs braking torque.   For cars, street pads are made to last a long time, not create too much dust or noise, and still give decent braking torque over moderate temperature ranges.    Race pads often make dust like crazy, squeal like mad (which is why they're fun to drive on the street), and don't last as long but make much greater braking torque over a much broader temperature range.   So getting good braking torque (or exceptional longevity) has a lot to do with the pad material, so I'm wondering what's available or whether there is any variation in compounds for typical Mooney brake pads.

Even on many race cars the rear brake rotors aren't ventilated, so they're similar to the thin rotors on an airplane.   It's common to use aggressive race pads on those, too.   They hold up decently doing a lot more work than the occasional single stop from 60-70 mph or so that a light airplane needs.   I think the rotors on the airplane will hold up to a lot more than what they're currently doing on mine, since they don't really need to do much relatively speaking.

My pedals are firm, so I think the fluid is fine and there's no air in the lines, and they're smooth and consistent so it seems like the rotors are fine.   There's just not a lot of torque.   On a race car the first go-to change for that situation would be moving to a more aggressive pad material.    "Conditioning" brakes to transfer pad material into the rotor face in a race application is called "bedding in", since racers are less family friendly, I suppose. 

I suspect that light aircraft pads are not made for high temperatures, which suggests the pads may be subject to glazing if they got overheated sometime in their life.   My annual inspection is due in May, so maybe we'll pop the pads out at that time and see if they've just gotten too hot somewhere along the way and glazed.    That'd be an easy fix.

And to Jim's point, going into short fields on occasion, or having to land long for whatever reason, it's always good to have useful brakes for when you need them.   Not having them when you could really make use of them is annoying at best and potentially expensive or dangerous at worst.    If there's a means to make them better, like other similar aircraft I've flown, I'm interested in figuring that out.

 

You only have two choices that I know of, OEM Cleveland pads or PMA'd RAPCO pads. Most of us use the cheaper RAPCO pads without complaint. Same for the disks, except you can get corrosion resistant stainless that Jim talked about above.

As Jim @bluehighwayflyer said above, if you can lock them up you're probably doing fine, but I would still check them over for glazing and if you're really disappointed with them (sounds like you are) just replace them when you have the opportunity and then properly condition them. You just might be pleasantly surprised. 

[EricJ]

Being able to lock up a wheel is not a good evaluation of the capability of a brake system.   Cheap pads on cheap rotors can (and easily do) lock up wheels on cars with not a ton of provocation, but can be easily out-performed in a non-lock-up situation with a superior braking system.    I can lock mine up, but that's counter-productive and doesn't really say anything about the ability of the brake to make torque when the tire is not in sliding friction.

 

[jetdriven]

I have the same problem I’ve noticed the Cleveland pads have a little more Brake torque then Rapco.  We actually pulled off the not very old Rapco set to make this change. 

[Guest]

www.apsbrakes.com also makes Pma’d brake parts.

Clarence

[kortopates]

5 hours ago, M20Doc said:

www.apsbrakes.com also makes Pma’d brake parts.

Clarence

Thanks for sharing.  These advertise like they could be an improvement over the others - any comments or opinions on their performance?

And still economical although sold in packs of 10. 

Edited March 8, 2018 by kortopates

[buddy]

I found that the brake fluid should be totally drained and replaced with new fluid every 2 years, this seems to solve the problem.

[DonMuncy]

1 minute ago, buddy said:

I found that the brake fluid should be totally drained and replaced with new fluid every 2 years, this seems to solve the problem.

I agree that would be a good idea. How do you think would be the best way. I surely wouldn't empty the system and then refill it. Would you put an overflow tube on the top of the reservoir and push from the bottom, or put a tube on the outlet at each wheel and push downward.

[Yetti]

Fill from the top and then bleed at the bottom.  that way you won't risk getting air in the system.  If you have air in the system then push from the bottom with oil can.

more aggressive brake pads would mean the rotors would go away faster.  Something has to give.   Also the pads are held on with two relatively small rivets.  It is probably one of the easier jobs on the plane to replace the pads.  Under supervision of course as while removing the brakes to replace the tire is OK for PM.... if the brake pads grow while brakes are off that would need an mechanics signature.

[N201MKTurbo]

I use an oil can from Pep Boys with a length of 1/4 inch clear vinyl tubing so you can see any bubbles. It is small, cheap, simple and works great.

[jaylw314]

15 hours ago, bluehighwayflyer said:

My experience is limited to C’s and J’s but I agree that Mooney brakes just suck.

That having been said, that is not so much a bad thing. I put new stainless steel discs and pads (and calipers and wheels, too, for that matter) on my J when I purchased it 12 years ago and the pads to this day show next to no wear. In normal operations you just rarely need the brakes and you should strive to use them as little as is possible. For most of us there is always another turn off and if there isn’t you are just flat out coming in too fast. 

Jim

How are the stainless steel rotors in terms of wear?  I've not had any experience with car rotors made out of stainless steel.  Stainless steel is not as strong, but the surface might be harder, so I don't know if it would wear better or worse.

As an aside, IIRC, "bedding" a brake pad is important for race-type pads, because they are more adhesive--they transfer the pad material to the rotor.  However, street pads are mostly abrasive--they turn to dust and do not transfer to the rotor, and the "bedding" process is simply to ensure the pad surface is worn to the same shape as the rotor surface.

Also, I think increased brake pad performance is important in car tires where an individual tire can be loaded to the car's full weight or more during weight transfer (turning/braking).  At that point, the tire can handle much more braking force, and the pad/rotor combo needs to be up to snuff.  On aircraft brakes, we don't get such changing loads, so the tire friction is the limiting factor.

[jaylw314]

12 minutes ago, bluehighwayflyer said:

I don't know, unfortunately, but have wondered the same thing about the effectiveness of stainless steel brake discs as compared to regular carbon steel.  Regardless, though, I prefer the stainless due to it's anti corrosion qualities. I don't need much braking authority anyway and I have more than enough as-is. 

Jim

Certainly the other benefit would be having nice and shiny brake rotors!

[EricJ]

56 minutes ago, jaylw314 said:

As an aside, IIRC, "bedding" a brake pad is important for race-type pads, because they are more adhesive--they transfer the pad material to the rotor.  However, street pads are mostly abrasive--they turn to dust and do not transfer to the rotor, and the "bedding" process is simply to ensure the pad surface is worn to the same shape as the rotor surface.

Also, I think increased brake pad performance is important in car tires where an individual tire can be loaded to the car's full weight or more during weight transfer (turning/braking).  At that point, the tire can handle much more braking force, and the pad/rotor combo needs to be up to snuff.  On aircraft brakes, we don't get such changing loads, so the tire friction is the limiting factor.

Most street pads require bedding as well, but you may not notice the effect as much as you would with a race pad.   You can often tell the type of compound used, even on a street pad, by the color of the rotor surface which reveals the transferred material.   Some pads leave a very nice blue color, some amber-ish, some grey.   They generally all transfer, though.

You're right that the engineering tradeoffs with a light aircraft are very different than for an automobile.   I'm just trying to figure out why my brakes suck so badly (which is apparently not uncommon on Mooneys) and what the options are for fixing or improving them.  One thing that occurred to me this morning is that Mooney engineering may have wanted to limit the brake torque to keep the weight transfer onto the nosewheel to a minimum to reduce the likelihood of a gear collapse.    Maybe I don't want so much brake torque after all. 

Automotive and truck brake rotors are typically cast iron.   Motorcycles often use steel, partly for cosmetic purposes.   Are light aircraft rotors typically steel?  I'd guess the weight advantage may drive that selection.

The Arrow I used to fly has a similar motor, weight and landing speed as the Mooney, but it actually slowed down when you pushed with your toes.   I'm interested in understanding the differences.

[jaylw314]

9 minutes ago, EricJ said:

The Arrow I used to fly has a similar motor, weight and landing speed as the Mooney, but it actually slowed down when you pushed with your toes.   I'm interested in understanding the differences.

If not the brake lines/calipers, are our brake pads different sized from other aircraft?  If they are larger, they might not develop the same brake pressure as a smaller pad.  Kind of like the difference between racing clutches and street clutches

[EricJ]

1 minute ago, jaylw314 said:

If not the brake lines/calipers, are our brake pads different sized from other aircraft?  If they are larger, they might not develop the same brake pressure as a smaller pad.  Kind of like the difference between racing clutches and street clutches

Good question.   One of the main parameters on a braking system is the piston size in the caliper (and in the master cyl), which determines the pressure on the pad (and is why adding a 2nd caliper or additional piston area helps).   If an Arrow or similar airplane (my buddy's Cherokee stops like a race car, I'm envious), has a larger caliper piston that would explain part of it.  I've no idea of the actual differences, though.