Date: Fri, 25 Mar 2005 08:44:19 -0500 From: Malt_Hound <Malt_Houndnospamm*yahoo.com> Subject: Re: 9-3 brake rotor
doug wrote: > When the car is running and the ABS system is energized, the > electro-magnetic solenoids are energized and the control valves are open. > Therefore, the minute amount of pressurized fluid required to move the > caliper a few thousandths of an inch can flow. And when the brakes are > released, the return action of the caliper piston seal and retraction of the > master cylinder piston does indeed cause that same minute amount of fluid to > return to the master cylinder. But remember, the valves are OPEN. This is by > design. > > When the ABS system is not energized, the valves are closed. Why would > anyone want to risk damaging the seat of these valves by forcing brake fluid > against them? If the seat is damaged, the anti-brake function is > compromised, as a leaking seat would not permit the hydraulic pressure to > the "locked up" wheel to be sealed off and diverted. > > doug I had not previously weighed in on this thread, mostly because I am not particularly well versed in ABS pump design. OTOH it seems that you are, Doug. I must confess that I have used the C-clamp method on a number of cars with ABS (including late model SAABs) and I've at least "gotten away with it", so perhaps these valves you mention are more hardy than you might imagine. At least anecdotal evidence seems to support that since there are a bunch of us testifying we have done so with no ill effect. In fact, I've yet to ever hear anyone say they botched their ABS by pushing back the calipers. In any case, based on your above description, could you not then simply turn the car ignition to on to activate the ABS valve, which would put it in the open position while you then push the caliper piston back? That would seem to satisfy your desire to not damage the valve(s) and at the same time leave the system sealed so as not to introduce air into the caliper circuit. Perhaps the best of both worlds? I believe that the "dirt in the system" argument is specious. If there is dirt in the system it will migrate throughout regardless of whether we push fluid back or not. Certainly, one should plan on flushing the brake fluid at regular intervals anyway, and this would mean there is no dirt. -Fred W
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