OK, so I'm hopelessly behind and reading a GRM from spring 2008 that had a story about brake maintenance. At the end, a little tip was "don't push in pistons without opening bleeder screws." Really? I've always removed dead pads and then just c-clamped or channel-locked the piston back.
Am I supposed to open the bleeder before doing this? Any caution about air getting in before I can get back to close the screw once the piston is retracted?
Thanks, Ron
In reply to glueguy:
Since most cars today have ABS, the preferred route is to open the bleed screw before compressing the piston. This helps minimize the chance of any foreign material getting pushed back through the brake lines and plugging the ABS components.
When I work on non-ABS cars I usually don't bother opening the screw, however I always do on an ABS car.
Paul
eastpark wrote: When I work on non-ABS cars I usually don't bother opening the screw, however I always do on an ABS car. Paul
Same here.
WooHoo! someone just referenced the article i wrote! glueguy, you're my new favorite stranger!
They pretty much nailed it as far as contamination goes, but there's another reason too: getting rid of skanky old fluid and replacing it with fresh new fluid. brake fluid degrades in two ways: it absorbs moisture through the porosity of the rubber hoses and the gasket inside the reservoir cap, and it also gets tiny little air bubbles throughout the fluid. the net effects of this fluid degradation over time are: reduced boiling point, potentially leading to fluid fade; and increased compressibility, leading to a spongy pedal.
Opening the bleeder screw when you push the pistons back is a simple way to get rid of a bunch of dirty fluid from the system, which reduces internal corrosion, raises fluid boiling point, and improves pedal feel. it's one of those "i'm already in here, i might as well do it" kind of things, like replacing the water pump when you're doing the timing belt.
I flush my brake fluid every two years, typically coinciding with a pad change. if your car is more than a few years old and it's never been done, you won't believe the improvement in pedal feel. yes, it's that dramatic.
As far as getting air into the caliper while the bleed screw is open: it doesn't come shooting out like during a normal bleed, since there's no pressure from the master cylinder. it just comes out in slow flow, but since the MC is higher than the caliper or wheel cylinder, the flow is always fluid out, not air in (unless you leave it open for longer than about 10 - 15 minutes and it completely drains that circuit of the MC) and you'll have plenty of time to get the bleed screw tightened before you run out of fluid from the MC.
Open the bleeder screw, push the piston in, close the bleed screw, clean up the mess, install new pads.
After you've done all four corners, fill the MC to the full mark. from then on, as long as there are no leaks in the system, you can use the fluid level in the MC as a general indicator of pad life. when the fluid level gets down near the min mark, it's time to check pad thickness.
Thanks, AngryCorvair, I'm honored....
Thanks for the tip. I started in pre-ABS days and missed that one. See, you changed the world, at least in a small way 
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