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- Newsgroups: rec.motorcycles
- Path: sparky!uunet!think.com!rpi!newsserver.pixel.kodak.com!laidbak!jeq
- From: jeq@i88.isc.com (Jonathan E. Quist)
- Subject: Re: Mechanism of brake hydraulics
- Message-ID: <1993Jan27.225926.7866@i88.isc.com>
- Sender: usenet@i88.isc.com (Usenet News)
- Nntp-Posting-Host: birdie.i88.isc.com
- Organization: Lachman Technology, Incorporated, Naperville, IL
- References: <C1I5H7.Cup@cgl.ucsf.edu>
- Date: Wed, 27 Jan 1993 22:59:26 GMT
- Lines: 40
-
- In article <C1I5H7.Cup@cgl.ucsf.edu> friedman@cgl.ucsf.edu (Simon friedman) writes:
- >Hello all,
- > I have what is probably a simple question to experienced people but is
- >confusing me: It concerns the hydraulic braking system. I recently changed
- ...
- >manual then goes on to say that to adjust to the new pad position, pump the
- >brake several times to expand the piston. This makes sence to me only if there
- >is some sort of one way valve that allows the hand lever piston (or whatever
- >its called) to introduce more brake fluid into the line, but doesn't allow it
- >to return. If it did allow it to return, one would never advance the piston
- >anywhere, it would just go back and forth.
-
- Good intuition so far...
-
- > My confusion is this: If the
- >hand lever can pump more fluid into the line to advance the piston to the new
- >pad position and prevent back flow, why doesn't the piston just get permanantly
- >jammed against the brake pad thereby producing constant braking?
- >Or is my assumption about the pumping action way off?
-
- You've got it essentially correct, though when the lever is fully released,
- the line should be open to the master cylinder to relieve pressure due
- to temperature changes (or overheating at the slave cylinder).
- The thing you're forgetting, which prevents the pistons from fully retracting
- on their own, is that seal friction prevents them from backing off.
- And, just to confuse things, the mechanism that backs the pistons off
- slightly when pressure is released is flex in the seals (which again works
- because of friction between the seals and pistons). In other words, when
- braking, the piston seals are slightly deformed, and when pressure is released
- and they return to normal, the pistons retract a bit.
-
- Thanks for the information go to the shop manual for the '72 Capri, where
- I cut my teeth on disk brakes. ("You wanna use my car? You make the
- brakes work so it's safe!" I think my Dad worked this one out with my
- Mom - she figured I couldn't do it, and he knew I would... Thanks, Dad!)
- --
- Jonathan E. Quist Lachman Technology, Incorporated
- jeq@i88.isc.com '71 CL450-K4 "Gleep", DoD #094 Naperville, IL
- __ There's nothing quite like the pitter-patter of little feet,
- \/ followed by the words "Daddy! Yay!"
-