![]() The milk containers are nice because you can use the hollow handle to push the tubing into where it will be held on one end while the other end will go over the bleeder screw (valve). I take used pint sized plastic milk containers and suspend them with bent coat hanger from the caliper or brake drum. Prepare yourself with some clear tubing and catch cans for the old fluid. Loosen the lug nuts, get the car up in the air on jack stands (if you DON’T know how to do this safely, DON’T do it yourself), and take off all the wheels. If you do your own brake bleeding and don’t have access to a vacuum bleeder you can take longer and bleed it in the traditional fashion of using the brake pedal to push out fluid and air. This will gas out as the new fluid is heated and the pedal will get spongy again. Vacuum bleeding is preferred since pressure bleeding actually introduces and dissolves air into the new fluid. Then the technician will ensure that new fluid is always kept in the brake fluid reservoir and pull it through the system starting at the brake bleeder farthest from the master cylinder. Then they will vacuum out the brake fluid reservoir of old fluid. The first thing they will do is remove all the wheels so they can get to the brake bleed screws. If your mechanic does it the right way they will use a vacuum bleeding system. What you should do, probably once a year, is have the old fluid flushed and completely replaced with fresh brake fluid. The water can react to oxidize brake components from the inside out. This means that the old – water soaked – tired – brake fluid will still be there. In fact, if you go to a garage and have a “brake job” done it is highly unlikely that they will do much more than bleed the brake lines. So what is the big deal? The big deal is that most of us never flush and replace our brake fluid. You will know because the brake pedal will start to feel mushy as the fluid overheats and the pedal may even go to the floor. The every day driver will find brake performance just fine by sticking with the fluid that the dealership recommends unless they use their vehicle to the extreme, such as a newspaper delivery route or negotiating their way down curvy mountain roads. Once you boil your brake fluid it will not recover and you MUST bleed and change out the fluid. The higher boiling points are critical to those of you that wish to spend time on a race track. Wet boiling points will also vary, but be well over 400 degrees. Some of the high performance fluids are rated well over 500 (to almost 600) degrees boiling point dry. The cost of brake fluid can vary as well from less than $0.20 an ounce to over $2.00 an ounce. Those are the DOT ratings mind you, and there are high performance brake fluids that exceed those ratings. DOT 4 raises the bar to 446 and 311 respectively. For DOT 3 the dry boiling point is at least 401 and the wet 284 degrees. The difference between the DOT (Department of Transportaion) ratings of brake fluid are the boiling point ranges that they achieve both dry (no water absorbed) and wet (about 3-4% water content). In fact the anti-freeze you use is probably glycol based just because it mixes well with water. Why do I mention water? The chemistry of DOT3 and DOT 4 brake fluids attract water. Since the disk rotor can and will generate over 1000 degrees (F) of heat and transfer 400 degrees or more to the caliper water is not a good fluid to choose. Water boils (sea level air pressure) at 212 degrees F (100 C). Notice that water is not listed as a component of brake fluid. It is this property not to compress that allows it to do its job well.īack to the chemistry. This pressure is then applied to the pads (or shoes) against the rotation of the brake rotor (or drum). Brake fluid is used to transmit pressure from the brake pedal to the extreme ends where the disk brake calipers or drum brake cylinders are. Let’s look at what brake fluid’s (and clutch fluid) real job is. There is another rating called DOT 5.1 that consists of borate esters. DOT 4 fluids are much like DOT 3 fluids, but also contain borate esters. If you want to look at brake fluids from a chemical standpoint DOT 3 fluids are based on glycol and glycol esters. A few will Use DOT 4, and very few will ever use DOT 5 which is a silicone based product. Most brake fluid that comes in a new car will be rated DOT 3. What are those things in the title? Brake fluid is categorized as one of those three ratings.
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