Van's Air Force
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Do Brake Pistons Wear?
- Thread starter Vlad
- Start date
az_gila
Well Known Member
I wondered the same thing working on the Cleveland brakes on my Tiger.
Very little help in the Maintenance Manual - The main snippets -
Inspect pistons for nicks or burrs. Check the piston tail for damage, and replace piston if damaged beyond repair. Remove nicks or burrs by hand polishing with 600 grit emery paper. Thoroughly clean part.
Installation of Pistons
Installation of pistons with an internal guide is the same as for other pistons. Care must be taken to insure that no damage to parts occurs during installation. If considerable effort is required, remove piston and inspect bore and pilot bore area for damage. If bore is damaged, check the corresponding area of piston for damage.
(a) Place piston in bore and rotate to seat friction spring (if applicable), and insure that piston and o-ring are in proper alignment. Press piston into bore by hand. Tap the piston squarely with a wooden or plastic mallet (if required) while rotating piston.
Lots of wear limit dimensions for the brake disks, but no numbers for piston or bore wear.
Very little help in the Maintenance Manual - The main snippets -
Inspect pistons for nicks or burrs. Check the piston tail for damage, and replace piston if damaged beyond repair. Remove nicks or burrs by hand polishing with 600 grit emery paper. Thoroughly clean part.
Installation of Pistons
Installation of pistons with an internal guide is the same as for other pistons. Care must be taken to insure that no damage to parts occurs during installation. If considerable effort is required, remove piston and inspect bore and pilot bore area for damage. If bore is damaged, check the corresponding area of piston for damage.
(a) Place piston in bore and rotate to seat friction spring (if applicable), and insure that piston and o-ring are in proper alignment. Press piston into bore by hand. Tap the piston squarely with a wooden or plastic mallet (if required) while rotating piston.
Lots of wear limit dimensions for the brake disks, but no numbers for piston or bore wear.
Warren what would be the defense against pitting? Other then flying nearly every day.
I recalled an excellent discussion which approached the matter from a different angle. The OP thought he had a piston-to-bore clearance problem, but it turned out his mechanic installed the pucks bass ackwards:
http://www.vansairforce.com/community/showthread.php?t=104995
(1) Cleveland wouldn't supply official dimensions when asked.
(2) There is nothing in the Cleveland manuals beyond "remove burrs and damage with 600 grit".
(3) Reported clearances in the field were from 0.002" to 0.010" (the wide range may be a matter of measurement accuracy.)
(4) If we assume not more than 100 lbs of leg pressure, a Shore 75 viton or nitrile o-ring should be safe at 0.010" clearance.
The piston really sort of floats in the bore, and should not wear much at all. If the bore is cylindrical, damage free, and diametrical clearance is 0.010"or less, I'd would think a good cleaning and new o-rings are all you need.
http://www.vansairforce.com/community/showthread.php?t=104995
(1) Cleveland wouldn't supply official dimensions when asked.
(2) There is nothing in the Cleveland manuals beyond "remove burrs and damage with 600 grit".
(3) Reported clearances in the field were from 0.002" to 0.010" (the wide range may be a matter of measurement accuracy.)
(4) If we assume not more than 100 lbs of leg pressure, a Shore 75 viton or nitrile o-ring should be safe at 0.010" clearance.
The piston really sort of floats in the bore, and should not wear much at all. If the bore is cylindrical, damage free, and diametrical clearance is 0.010"or less, I'd would think a good cleaning and new o-rings are all you need.
rightrudder
Well Known Member
Vlad, how often are you replacing brake pads and rotors? I'm curious to see how much my brakes have worn when I take them apart at the first annual inspection (Jan. 2017).
Wear your brake pads out as fast as you can.......
If you don't use your brakes, the pistons will stay deep in the cylinder and keep the cyl walls exposed to the environment.
There is really nothing you can do.
From my automotive background, I believe some pitting also can be tied to moisture in the system. Just like a car, sitting is probably the worst issue our planes have. Probably just like all of us also as we age, ever notice in general those that live long and happy lives tend to not sit around the house?
That's certainly possible for those who are using automotive brake fluid, which is hygroscopic, i.e. attracts water from the air.
MIL-5606 and 83282 fluids are not hygroscopic, which is why the MIL spec says it may be stored in closed or open containers, and why we don't need sealed caps on our brake reservoirs.
To Vlad's question (pitting), I'd venture the real risk is atmospheric and water-borne corrosives finding their way into the annular space outboard of the o-ring. An example might be salt water, given Vlad's irresistible attraction to beach landings
I am on my third set of rotors. This is how they look after 1,700 hours the first set I replaced too fast (950h) could have ground some more meat from them.
I go through a set of linings in couple hundred hours. The more your rotors worn the more uneven the wear is the more often you replace the pads. I really experimented with this set. Don't go that far they were dead a while ago.
Captain_John
Well Known Member
So, does anyone ever try to resurface the rotors with say, a scotchbrite pad or sandpaper before re-assembly when installing new pads?
Would that lengthen the TBO?
Any benefits or drawbacks?
I am thinking of doing it just to make me feel better about a nice clean re-assembly.
CJ
Would that lengthen the TBO?
Any benefits or drawbacks?
I am thinking of doing it just to make me feel better about a nice clean re-assembly.
CJI am on my third set of rotors. This is how they look after 1,700 hours the first set I replaced too fast (950h) could have ground some more meat from them.
I go through a set of linings in couple hundred hours. The more your rotors worn the more uneven the wear is the more often you replace the pads. I really experimented with this set. Don't go that far they were dead a while ago.
Vlad, check Aircraft Spruce for Rapco Discs... They have a set that are 50% thicker than Van's stock ones. You will need a 1/8" spacer for your plate. And 1/8" longer bolts.
Or you can just purchase their expensive kit...... The end results is the thicker discs absorb a lot more heat. I have been running them for three years and there appears to be no heat line at all.
I have a 6A and do use my brakes.
So, does anyone ever try to resurface the rotors with say, a scotchbrite pad or sandpaper before re-assembly when installing new pads?
Would that lengthen the TBO?
Any benefits or drawbacks?
I am thinking of doing it just to make me feel better about a nice clean re-assembly.
There is a published WEAR limit on the discs that is very small.
From the Cleveland Service Manual the 164-01700 Disc we used has a minimum thickness of 0.167". Most of us in the RV world wear them past that limit and they really should be replaced sooner than most of us do.
