Matco Brake Question

[Rogerck]

We have about 60 hours on our 06SW, with tundra tires, since the Matco brakes were installed.  The brakes still do not have the stopping authority I would expect.  With full braking pressure I can not get the wheels to lock (as a test) and the plane starts to creep at 3400 rpm run up.  The original Marc brakes actually had better stopping power during taxi and run up operations than the Matco's.

 

The brakes have been bled several times (with a pressure bleeding pump) and no bubbles can be seen in any of the lines.  The brake handle pressure is firm, not mushy.

 

The brakes have been "broken in" by high speed taxi braking in accordance with Matco's instructions.  This has been done three times.

 

The discs are clean and dry.   

 

After the initial installation, there was a small seepage at the left bleed fitting. Discs have been cleaned with solvent several times.  The brakes do not pull to one side as might be expected if the disc or pads were contaminated.

 

Any suggestions, or am I expecting too much braking authority?  

 

Roger Kuhn

 

 

 

 

[Anticept]

Are the rotors glazed?

 

Also you mentioned that you installed the matco brakes, did you also install the matco master cylinder? Roger was telling me that if you don't use the matco master cylinder with their brakes, you lose some effectiveness.

[Rogerck]

Yes, I have the Matco master cylinder.

 

Roger K.

[LS Bruce]

The Matco master piston is .625 diameter vs the Marc 16mm (.630 dia).

This is nearly identical area, pressure and volume out of the master cylinder.

My 2008 CTLS converted to Matco behaves almost the same as Rogerck's. However, mine will hold under full static run-up power.

[Rogerck]

Here are the conditioning instructions from the Matco manual.  Note that the process is supposed to "add a glaze to the disks" and that the glazing can be worn off if the taxi braking is too light.  This seems to counter what some have suggested.

 

Roger Kuhn

P. CONDITIONING PROCEDURES

NOTE It is important to condition the new linings after
installation to obtain maximum service life and
performance. The following procedures show when and
how this should be done.

Apply brake pressure during high throttle static run up ( note
The RPM at creep, if any.)

Perform two or three high speed taxi snubs (apply firm
braking from 30-40 mph down to 5 mph) to generate the
necessary 300 - 400 degrees at brake pads. DO NOT bring the
aircraft to a complete stop during taxi snubs, and continue to
roll the aircraft until reaching the tie down area Release brake
pressure as soon as practical, and park with brake pressure
released.

3. Allow brakes to cool for 10-15 minutes.

Repeat step # one and note RPM at creep if any occurs. There
should be a noticeable increase in holding torque.

(repeat steps one through three if necessary)

NOTE forward movement of the aircraft while testing
brakes, could be caused by skidding and not brake
malfunction. Use caution when breaking heavy on
aircraft with a tail-wheel as it could cause the tail
to lift from the ground.

Conditioning removes high spots, and creates a layer of glazed
material ( shiney appearance) at the disk surface. Normal braking
will produce enough heat to maintain glazing during the life of the
lining. Glazing can be worn off during light use such as taxiing
and occasional reconditioning may be required.

[Anticept]

That's odd. I will be very interested in what Roger has to say, because glazing is universally panned in all brake systems, from aviation, to automotive, to military, to be a BAD thing. Glaze creates poor friction characteristics due to the smooth surface.

 

Maybe matco mistakenly used the wrong word?

[sandpiper]

Sometimes you have to 'feather' the brake handle when the master is on to get full hold.  And sometimes you need to feather the brakes a bit to fully release them.  And you always need to feather them (pull moderately on the handle then release and pull again) when slowing in taxi or you will overheat them.

As much as I have to continually feather the brakes during taxi (in order to keep speed down to 10-11K at 1800 RPM which is bottom of the green),I have been surprised at the longevity of the pads. Just prior to my first annual after Matco installation I ordered new pads anticipating their demise. Still haven't needed those pads after 3 years.

[FlyingMonkey]

I should finish a fresh Matco install this week, I'll let you all know how it goes using the Matco break-in procedure (the one mine came with is the same as above).

[Anticept]

I just ordered a matco set from roger 2 hours ago myself.

[Runtoeat]

Excellent wear and always holds on static runups with matco's on my CTSW.  Perhaps I've gotten the glaze the break-in instructions indicate is a "good thing" because I need to pull hard on the brake handle to make high speed slow downs for quick upcoming runway exits.  I've always been told glazing ins a "bad thing" too.  All in all, I'm happy I installed them when I consider they allowed me to set my toe-in and camber.

 

Roger K, bottom line is the matco's on my plane don't lock up my wheels and it seems that they could bring the plane down a little faster when I need to really make a quick exit at speed but they always hold the plane during static run-ups.  I'll add that I have no brake shutter or "chatter" during application on taxi as I've seen the Italian brakes do on other CT's.  Component costs for parts and life of the pads is excellent.

[Rogerck]

I did two "reconditioning" brake snubs per Matco's instructions and the brakes hold better on run up.  Regarding runway braking, I'm with Dick H.  It seems to take a fairly strong pull to slow down fast, say to make an short upcoming runway exit.  Perhaps this is normal and this is what I'm trying to determine.

 

I did have Matco's on my RV6 with toe brakes and the stopping power was much more forceful.  But, these were different master cylinders, calipers, etc. and may not be a good comparison.

 

Roger Kuhn

[Rogerck]

I started this thread and did want to provide feedback on the resolution of my brake holding problem.  When the Matco's were installed, there was a small leakage of fluid at the brake tube connections to the calipers on each side, due to an incorrect tubing fitting.  The correct fitting was installed and the leakage was fixed.  We wiped down the small amount of fluid on each outside caliper housing.  The disks were also wiped and appeared clean.  In retrospect, some small amount of hydraulic fluid reached the pads, likely from prop wash while taxi testing.  When I spoke to George at Matco, he indicated than any fluid coming into contact with the pads will contaminate them and reduce performance.  Furthermore, the pads can not be cleaned.  We  wound up replacing the pads and cleaning the discs with solvent.  Problem resolved.