| RE:Brakes 101 |
Subject: RE:Brakes 101 by SJW on 2006/2/2 21:16:26 These guys have given you good advice, but I would suggest you go ahead and bleed the system, even though it's technically not likely to be mandatory. Dot 3 brake fluid is hygroscopic, which means it'll absorb moisture from the atmosphere. Over time, this contributes to corrosion within the hydraulic system, causing problems with calipers, master cylinders, rusted-out and ruptured steel brake lines, etc. The boiling point of DOT 3 will also lowered if it has taken on moisture, and that's not a good thing, especially in a car that's driven and braked aggressively (such as on a road course). Also, because of DOT 3's hygroscopic nature, you should always only use fluid that's in an unopened or well-sealed container. I only buy the smallest bottles of fluid, so that I don't end up storing a partial container that has a lot of air in it, and if I have a small bottle that's nearly empty, I won't use the remaining fluid after it's been stored. As inexpensive as DOT 3 is, I'd prefer to work from a virgin bottle. If you bleed/flush your brake system every year or two, it'll go a long way toward keeping the hydraulic system gremlins at bay. If you neglect to do this basic maintenance chore periodically, it'll eventually come back to bite you in the wallet. Since you'll be that far into it, with the wheels removed, might as well go ahead and bleed 'em while your at it. It's never easier than when the car's already in the air, and the wheels are off, so now's as good a time as any. As a bonus, if you disturb the bleeder screws every year or two, they'll never seize on you. Recommendation: Use a clean (virgin is best) turkey baster to suck the master cylinder reservoir dry. Crack each bleeder screw open for only an instant, then re-seat it. This is done only to make sure the bleeder isn't seized. If it is, the sooner you learn this, the better. If you end up needing to replace the caliper cuz the bleeder's seized, you'll be glad to find this out before you go any further. Remove the pads as outlined by Bruthish, and press the pistons fully into the calipers with the C-clamp (don't go crazy with the pressure, just push 'em all the way back in). This will force as much as possible of the existing fluid in the system back up into the M/C reservoir. Suck the reservoir dry again with the baster after pushing each piston back in, to make sure the M/C reservoir doesn't overflow and make a mess under your hood. You now have a system that has relatively little fluid remaining in it. Install the new pads, and mount & secure the calipers. Leave the wheels off for now. Before you step on the pedal (which would push the pistons back out again), gravity bleed the system. To do this: 1. Fill the M/C reservoir up with virgin fluid. 2. Put a length of hose on the bleeder screw at each wheel. This hose should be sized so that it will fit snugly over the bleeder, and stay put when you let go of it. I use clear plastic hose (polyethylene, if I recall correctly) that can be purchased at Home Depot / Lowe's in various diameters. For some bleeders, air line tubing that's used in fish tanks works well. The advantage to using clear tubing is that you can watch what's coming out of the calipers as it's bleeding. This allows you to check for air bubbles and to monitor how fresh (or not) the fluid is as it exits the system during the bleeding process. 3. Stick the loose end of each hose into a container to catch the fluid that will be released. 4. Crack each bleeder screw open. A quarter-turn or so should do just fine. 5. Crack a cold beer open. A quarter-turn or so should do just fine here, too. 6. Grab a chair. 7. Drink the cold beer. 8. Get up every 5 or 10 minutes, and check the M/C reservoir fluid level. Refill as it drops. Make sure it never runs completely dry, or air will enter the system, and you'll have a more lengthy bleeding process to remove it. 9. Repeat steps 5 through 8 until the fluid that's coming out of the bleeders looks as clear and fresh as the fluid you're putting into the system, then close the bleeders, remove the hoses and containers, and top off the M/C reservoir. Wipe residual fluid, if any, off of the calipers, etc so that none ends up on the tires. Brake fluid is NOT good for your tires. When you've finished bleeding the system, step on the pedal a few times, going only around 1/2 way to the floor with the pedal on each stroke (you're only going 1/2 way down so that you won't run the risk of tripping the warning light switch). After a few strokes, check the fluid level in the M/C reservoir again. What you're doing now is pushing the caliper pistons back out as far as they'll go, to their normal resting position. This will draw fuild out of the reservoir, so keep checking it to make sure it doesn't run dry. If it runs dry, it'll suck air into the system, and you'll have to repeat the bleeding process to get the air back out. Repeat this work-the-pedal / check the fluid level process until you get a firm pedal under your foot. If you neglect do do this process, the pedal will go straight to the floor when you step on it, cuz the pistons will still be recessed in the caliper bores. This can lead to Very Bad Things happening if you test drive the car before you've obtained a firm pedal -- it's the sort of nasty surprise nobody needs. Gravity bleeding is the lazy man's way to bleed brakes, and it requires no pedal pushing or special equipment. You don't have to recruit your wife to work the pedal while you work the bleeders, you don't need speed bleeders (they are pretty cool, though), and you don't need a pressure bleeder. Speed bleeders and pressure bleeders are faster, but if you're not in a hurry, gravity bleeding will get the job done just fine, and as far as I'm concerned, any job that will do itself while I drink cold beer is a fine job indeed. If the car has ABS, follow the procedure in the Factory Service Manual in order to achieve a full system flush/bleed. Be well, SJW |
