That’s where an on-car lathe is superior. It turns the rotor while mounted to the hub so that both assemblies are trued when the rotor is machined. The on-car lathe cannot machine drums, so they must either be removed for machining or replaced with new.
Caliper Inspection
One of the main areas to inspect the calipers are the slides or pins that the caliper must move on as the brakes are applied and released. As your vehicle ages, rust and corrosion can develop between the moving parts, creating issues. Calipers must be removed, surfaces properly lubricated, and parts replaced as necessary.
Binding slides cause uneven pad wear, possible noise, and inadequate braking. The pistons must be able to be pressed back into their bores if the calipers aren’t going to be replaced to allow room for the installation of the new brake pads. The pistons are extended out of their bores because of pad wear; fluid had to take up that space behind the piston. This is also why the fluid level in the master cylinder drops as the pads wear.
Another reason that the fluid level drops is a leak in the system, but that would likely be accompanied by a sinking pedal, fluid on the ground, and a red brake warning light on the dash. Most of the time, the master cylinder is completely empty if a leak were present.
Service
Caution: Some newer vehicles with electronic brake systems require a scan tool for servicing. (See “New Technology Precautions” at the end of this chapter before servicing a vehicle with an electronic brake system.)
Be sure to observe all safety precautions when performing brake service, including the use of wheel chocks, proper jack use and jack stands, safety glasses, ear protection, and disposable gloves. It is also wise to have good ventilation in the area and a fire extinguisher nearby.
Brake Fluid Condition
Brake fluid degrades over time. As fluid ages, it loses some of its additives. Although brake test strips are available to see if your fluid needs to be replaced, it’s a good idea to replace it during brake servicing.
Although some manufacturers don’t specifically recommend a replacement interval other than during hydraulic repair, it is a good idea to begin the job by using a turkey baster to remove all of the old brake fluid from the master cylinder. Immediately fill the master cylinder to the maximum mark with the correct fluid and install the lid.
Brake fluid test strips are available to determine the condition of the fluid. They detect the level of copper present to determine fluid age and additive degradation. If the fluid is in need of replacement, the test strip turns purple within a minute of being immersed in the fluid.
Common Hand Tools Come in Handy
Most tools needed for disc brake repair can be found in the average do-it-yourselfer’s toolbox. Bolts are generally metric in the range of 10 to 21 mm. Some vehicles use Torx or Allen-head fasteners. A torque wrench is needed to be sure all fasteners are safely tightened.
Tools for pushing back calipers are extremely handy but a C-clamp can be used against one of the old brake pads in most cases on the front. To push back rear caliper pistons that use integral parking brakes, a special tool that rotates the piston as it goes in is extremely useful.
If you are doing drum brake work, you need some inexpensive tools to remove and install hold-down and return springs. Tubing wrenches are the best for removing hydraulic fittings. A floor jack, jack stands, and wheel chocks are required for safe hoisting. ■
A color chart is supplied with the test strips. After the strip is immersed in fluid from the master cylinder, it begins to change color if the fluid contains high levels of copper. If it becomes dark purple, a fluid change is needed.
Most vehicles require DOT 3 brake fluid, but you should always check the vehicle manufacturer’s specification. Put the cap back on the brake fluid bottle immediately because an open container absorbs moisture from the atmosphere and the fluid is ruined in a short time. It is also wise to buy small bottles of fluid for this reason.
Remember that brake fluid takes paint off quickly, so be careful where you place your hands after handling brake fluid and don’t let any fluid drip on a painted surface. If it does, flush the surface with water immediately!
Brake Bleeder Removal
After you have raised and supported the vehicle, make sure the brake bleeders can be opened. This is necessary because the piston(s) in the caliper must be pressed back into its bore to allow room for the new, thicker brake pads. Also, the bleeder should be opened to allow potentially dirty fluid to escape instead of traveling upstream. If a bleeder is stuck, lightly tap straight onto it with a ball-peen hammer and use a six-point wrench or socket. Tighten it a bit first and then loosen it. Tapping around the bleeder on the caliper can also help to loosen it. Do not use heat, which can damage internal rubber components.
Test Strips Determine Amount of Copper
It is difficult to tell if brake fluid is bad by looking at the color of it. It naturally absorbs dye from the rubber components and turns darker as it ages, and most manufacturers don’t have service intervals listed in the manual. A pretty common guideline is to replace the fluid every time the system is opened for service. A handful of manufacturers have a time interval, such as 24 months, but most do not specify a time or mileage interval.
Until recently, most professionals used a battery-powered device to determine the boiling point of the fluid, but now most are using test strips in the master cylinder reservoir. These strips determine the copper content of the fluid. The older the fluid, the more copper it has absorbed from the steel brake lines. This is an indication of age and additive degradation. The Society of Automotive Engineers (SAE) has determined that brake fluid with 200 ppm (parts per million) of copper or more should be replaced. ■
Vacuum Bleeder Option
It is a good idea to first remove all of the old brake fluid from the master cylinder reservoir and pour in new fluid. This step keeps old fluid from entering the master cylinder and ABS unit when the system is opened up downstream. Brake vacuum bleeders are available for this purpose, but a common turkey baster works great if you have a container under the hood with you to squirt the old fluid into. Once the old fluid is out, you can pour in the correct fluid to the maximum line. The reservoir cap has the recommended fluid listed on it. ■
Prior to beginning the brake job, it is a good idea to use a vacuum bleeder or turkey baster to remove the old fluid from the master cylinder reservoir. This prevents old fluid from flowing through the master cylinder and into the ABS modulator.
After the old fluid is removed, pour in new brake fluid until it is between the minimum and maximum mark on the master cylinder reservoir. When the calipers are removed or the bleeder is opened, new fluid circulates through the master cylinder and ABS modulator instead of old fluid.
If the old calipers are to be reused, the bleeders must be checked to see if they open before starting the job. If they are unable to be opened without breakage, replacement calipers may be required. It is a good idea to open the bleeders prior to pushing back the caliper piston so that the old fluid can escape instead of flowing upstream through the ABS modulator