speedgene
Zone Head
Posts: 996
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posted January 02, 2006 12:45 AM
With the 12 on stands, does your front wheel spin good? A revision
If someone did cover the brake caliper theory on the orginal post, I apologize. I did not read every page. I will though. The title of this post was a good question, and got my attention.
Not much has changed through the years with brake calipers. There is a seal called a "Quad" seal. The Q (I will call it) is round, but is unique with 4 square sides. The Q rests in a machined groove in the caliper. When the piston is at rest, the Q is square to the groove it sits in.
When pressure is applied, the fluid behind the piston, pushes the brake pad into the disc. By releasing the brake lever, the pressure is relieved behind the caliper piston barrel, and the pad moves away from the disc.
The Q-seal has what's known as "memory." Take a rubber band, stretch it and let it return to "memory." The Q acts the same way. The Q-ring pulls the piston away from the caliper when you release the lever. It is powerful enough to move right back to it's original (memory) shape, and pull the piston back with it.
Brake fluid is no longer compressed. The fluid moving back toward the M/C returns to (14.7psi) atmospheric pressure. Vacuum is non-existent. The Q is the only mechanical action that is moving the piston back into the caliper.
Water is heavier than water. When this enters the brake fluid system, water will (heat) turn into a crystal soild, and begin to grow between the caliper's machined housing and the Q-ring.
The Q is now compromised, and begins to distort. There are two actions from the crystallization. First, the crystal build-up prevents the Q's flat surface from returning to square. The second is the added surrounding (friction) pressure to the piston. This keeps the piston from moving at all as well.
This is usually the cause of slow dragging wheels. Dirty caliper grooves will need cleaning.
Remove the Q-ring and replace with new. Take a dentist pick and clean the crystal from the groove. The groove must be free of (all) white powder before reassembly.
Clean the piston with "0000" grade steel wool. Use no sand paper. All you are doing is leveling the tiny raised stubs on the piston. Nothing but a paper towel should be used to clean the inside of the piston (caliper) housing.
Lines, scrapes, dings, on the piston can still be useable, as long as it holds back the fluid. Removing the dust cover is pliable enough to serve no performance advantage. If you want to count ounces off un-sprung weight, go for it. The exposed piston (with the dust cover removed) will work fine. Damage to the piston should be minimal.
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fish_antlers
Administrator
The Truth is Out There
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posted January 02, 2006 01:38 AM
http://www.bikeland.org/board/viewthread.php?FID=1&TID=20941&set_time=1136194638
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What business is it of yours where I'm from, Friendo?
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Y2KZX12R
Needs a job
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Posts: 3762
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posted January 02, 2006 06:33 AM
Its funny this topic came up. I havent touched the brake system in years.
I did braided lines and EBC HH pads right off the bat in 2000, and just annual fluid changes sence. The brakes were starting to feal soft even with no air in the system. I knew the pads were getting down there but when i took them off they were thinner than I usually would let them get. :
So anyway, I stripped down the calipers and sure as shit. Corrosion of the calipers started around the seals between the caliper halves. The bores and pistons are like new and the seal groves are clean.
It looks like its just going to get a seal kit and pads.
I guess I should take apart the rear while i'm at it.
Are you guys finding any corrosion in your calipers?
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Y2KZX12R
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Y2KZX12R
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posted January 02, 2006 02:45 PM
Yo Fish, I moved the post here. (SEE ABOVE)
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Y2KZX12R
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Y2KZX12R
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posted January 02, 2006 02:46 PM
Hey my wife says all my posts are very dry. What the hell does that mean? Like dry humor? WTF?
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Y2KZX12R
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Y2KZX12R
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posted January 02, 2006 02:55 PM
I'm no chemestry major but I was thinking that it was more electralisis. Doesnt aluminum act as an anode or cathode (I forget) to water and ferris metals or somthing...? I wonder what the ph of that water is thats suspended in the brake fluid. Could be some ion exchange thing going on.??
Cant imagine how bad the corrosion could be if it had the original fluid in it.
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speedgene
Zone Head
Posts: 996
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posted January 02, 2006 04:10 PM
The tiny (condensation) air gap between the filler cap and fluid is all it takes to do the Ferris Bueller on the aluminum to catheterize the cavity with a foreign liquid.
Is this what your wife meant by corrosively dry humor Y2K??
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Ra12r
Zone Head
Posts: 919
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posted January 02, 2006 06:36 PM
Speedgene, that is a very good post....... thanks. I am glad that you did not post the above technical information in the other thread, as it would have been lost in the noise.
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All must bow to the "Ra Supremecy"...
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