#BLEEDING MASTER CYLINDER SERIES#

Once the pedal is firm, test drive the vehicle above 4 mph and the ECU will self test which includes homing the pistons.

If the rear pistons are not in their homed position, the front wheel circuits can be bled until a firm pedal is obtained. The other method should only be used when necessary. The first is to use a bi-directional scan tool, such as the Tech 1 or 2, to command the rear circuit motor to home the piston. There are two other methods of homing the rear circuit pistons. Making sure the pistons are in the home position ensures that the fluid path to the rear brakes is open to allow bleeding the system without a scan tool (See Figure 9). This step is not that important for the front circuits, but is critical for the rears (center gear). This places all of the pistons in what is referred to as the home position. It is important before installing the motor pack to rotate the gears on the modulator in a counterclockwise direction until they stop (Figure 8). While this article’s purpose is not to cover the process of modulator replacement I want to take a minute and cover the most important step about putting this system back together. As with any bleeder screw, these are placed at the highest point of the modulator, which on the Delco VI is at the solenoids.īleeding of the Delco VI will be required under the following conditions: While this group isn’t very large, there are enough of them to include in this article. The Delco VI represents the group of modulators equipped with bleeder screw(s).

#BLEEDING MASTER CYLINDER SERIES#

In addition, the system was used on the “F” series Camaro and Firebird and many Saturn vehicles. The Delco VI ABS system (See Figure 7) is a four-wheel, three-channel system that was used from 1992 until 1999 on a large number of General Motors FWD vehicles. Once the bleed function has been performed, the system should be bled at the wheels using the appropriate sequence.Ĭase Study 2 – Modulator Replacement on a Delco VI – 4-wheel ABS system. Other systems, such as the TEVES VI and some of the import systems, require the use of a dedicated bleed tool to perform a similar process. This function cycles each of the dump valves and then energizes the pump to bleed these hidden areas. For example, the Ford version of the EBC310 requires the “bleed function” to be performed through the NGS scan tool (See Figure 6). The majority of ABS modulators not equipped with bleeders will require cycling of the valves and activation of the pump to bleed out these “hidden” areas. The fluid paths to the dump valve, pump and low pressure accumulator represent a “dead end” and will not bleed without additional steps (Figure 5). The fluid flow during wheel-based bleeding is from the master cylinder through the normally open isolation valve and out to the system. Figure 4 shows the fluid path through the left front wheel channel. The red section represents the areas that will not be effectively bled when performing wheel-based bleeding. The green section represents the area that can be bled through wheel based bleeding. In terms of bleeding, the HCU (hydraulic Control Unit) can be divided into two parts, as shown in Figure 3. Each channel uses an isolation and dump valve so the HCU has six total valves, while the four-channel EBC410 has four pairs (See Figure 2).

These systems are three channel (except EBC410 – 4 channel) systems that use two position solenoid valves for pressure modulation, two low pressure accumulators and also incorporates a two-piston pump. Including the EBC410 adds Windstar vans from 1995 to 1999. These three systems represent the majority of light trucks equipped with 4-wheel ABS from 1995 up to the early 2000’s. We will do this on a case study basis.Ĭase Study 1 – Modulator replacement on a Kelsey Hayes BC310/EBC325/EBC410 – 4-wheel ABS system. While it is not possible to cover all the ABS systems in use, we can cover representative systems from the major categories when it comes to bleeding. The only thing to keep in mind is that the brake lights are on so if the job is going to be a long one, it is best to disconnect the stoplight switch. This will prevent the system from draining during service. This simple step moves the cup seals in the master cylinder past the vent ports which blocks the fluid path to the reservoir. There is a simple step when performing upstream hydraulic repairs that will prevent the system from draining, thus avoiding some of these headaches.įigure 1 shows a brake pedal depressor installed on a vehicle receiving hydraulic service. If air is allowed to enter, it may require special steps and/or tools to remove it. This is true as long as no air is allowed to enter the modulator. Typically, when performing wheel-based hydraulic repairs, no special steps are needed to bleed the ABS modulator.

Bleeding master cylinder