Tag Archives: abs

SI-Drive 2008+ STi Explained:

SI-Drive 2008+ STi Explained:

The 2008 Subaru Impreza WRX STI has a heritage of power and control. Previous models have been the foundations for countless racing victories and championships. The new WRX STI promises the same with it’s 305- horsepower, turbocharged, intercooled Boxer engine and a six-speed manual transmission.

SI-Drive: he new WRX STI promises the same with it's 305- horsepower, turbocharged, intercooled Boxer engine and a six-speed manual transmission.
SI-Drive: he new WRX STI promises the same with it’s 305- horsepower, turbocharged, intercooled Boxer engine and a six-speed manual transmission.

Power and control incorporate enchanced technology. As suggested by new switchgear on the dashboard and center console and my markings within the instrument cluster’s center-mounted tachometer, a driver has some things to learn before wringing out the most from the car.

Today’s electronics now allow the driver to tinker with engine response characteristics, the manner in which All-Wheel-Drive system fights for traction, and the degree to which braking and engine management help maintain vehicle stability. These capabilities are made possible by standard Vehicle Dynamics Control (VDC), Driver Controlled Center Differential (DCCD), and Subaru Intelligent Drive (SI-Drive).

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ABS 5.3 Antilock Brake System for Early Subaru Part 5:

ABS 5.3 Antilock Brake System for Early Subaru Part 5:

 

ABS 5.3 Antilock Brake System for Early Subaru Part 5: Beginning in approximately December of 1996, a new antilock braking system called ABS 5.3 was installed on Legacy vehicles equipped with ABS.
ABS 5.3 Antilock Brake System for Early Subaru Part 5:
Beginning in approximately December of 1996, a new antilock braking system called ABS 5.3 was installed on Legacy vehicles equipped with ABS.

 

Beginning in approximately December of 1996, a new antilock braking system called ABS 5.3 was installed on Legacy vehicles equipped with ABS. This system uses a Bosch hydraulic control unit and a Nippon electronic control unit. ABS 5.3 is a four channel control design which can independently control the front wheels and utilize select low control to control the rear wheels (a system which provides the same fluid pressure control for the two rear wheels if either wheel starts to lock up).

Although similar to other Subaru ABS systems, there have been enhancements to component operation and location. Diagnosis has also improved because of the ability of the 5.3 ABS system to communicate with the Select Monitor. The hydraulic control unit or HCU is located under the hood on the right side of the engine compartment. The size of the HCU has decreased by approximately a third from that of the ABS-2E system, used on previous model year vehicles.

The HCU controls brake fluid flow by utilizing eight solenoid valves. There is an inlet solenoid valve and an outlet solenoid valve for each wheel. Mechanically, the inlet solenoid valve is open during normal braking, and the outlet solenoid valve is closed. The HCU also contains a motor and pump assembly, which operates only while ABS is actively controlling the brake fluid flow–preventing a wheel lock.

Beginning in approximately December of 1996, a new antilock braking system called ABS 5.3 was installed on Legacy vehicles equipped with ABS.
ABS 5.3: Beginning in approximately December of 1996, a new antilock braking system called ABS 5.3 was installed on Legacy vehicles equipped with ABS.

Externally the HCU of the ABS 5.3 has a relay box attached. This allows troubleshooting of the valve and motor relay area to be kept separate from the troubleshooting of the solenoid valves and pump motor. There are four modes of operation for the ABS 5.3 system. They are normal, pressure-drop, pressure-hold and pressure-increase. When wheel lockup is sensed, Mode Two, Mode Three and Mode Four may be activated. They are described as follows:

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ABS for Early Subaru Part 4:

ABS Brake System for Early Subaru Part 4:

Troubleshooting Process:

To troubleshoot ABS systems, it’s best to follow a step-by-step procedure like the one on the 1992 Legacy ABS-2E Service Manual Supplement. Enter the flow diagram with the symptom reported on the repair order.

ABS Brake System for Early Subaru Part 4: The Subaru Legacy RS was known for using this ABS System.
ABS Brake System for Early Subaru Part 4: The Subaru Legacy RS was known for using this ABS System.

The diagram calls that Trouble Occurs. The first step in the procedure is “Basic Checks.” This calls for a visual inspection to look for obvious problems and includes the following items:

• improper battery voltage
• low brake fluid level
• brake fluid leaks
• brake drag
• condition of the brake pads and rotors
• size, type, and condition of the tires (Check the tires to confirm that they are the correct tires for the vehicle, that they are in good condition, and that they are inflated to the correct pressure).

If you find something wrong at this stage, correct it and see whether it eliminates the reported symptom. If not, continue to Step 3. Step 3 is Self-diagnosis. At this time, put the ECU into self-diagnostic mode, and monitor the ABS warning lamp for trouble codes.

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Antilock Brake System for Early Subaru Part 3:

Antilock Brake System for Early Subaru Part 3:

Damping Oscillations:

An additional benefit of this arrangement is that the mechanical valve damps out some of the unwanted oscillation in the brake pedal as the ABS pump runs. Because of this, the F valve used on the ABS-2SL system is no longer needed and has been eliminated from the circuit.

Antilock Brake System for Early Subaru Part 3: The Legacy RS rally car benefited greatly from having a superior ABS unit.
Antilock Brake System for Early Subaru Part 3: The Legacy RS rally car benefited greatly from having a superior ABS unit.

 

ABS Operating Modes:

To illustrate the four operating modes of this ABS system, we’ll assume that the ECU is operating only the solenoid for the right rear brake circuit. Recall that this circuit also affects the left rear brake circuit through the mechanical valve.

Normal Braking:

• Driver depressing pedal

• ECU passive (monitoring)

• Zero current in solenoid valves

• Pump off

• Plunger piston full right, pressure port open

• Master cylinder pressure supplied to all wheel cylinders

Pressure-Reduce:

• Pump pressure raising pedal

• ECU controlling solenoid valves and pump

• Full current in the right rear solenoid valve

• Pump running

• Plunger piston moves left, closes pressure port; system balances the two rear wheel cylinders.

Pressure-Hold:

• Pedal firm

• ECU controlling solenoid valves and pump

• Half current in the right rear solenoid valve

• Pump Off

• Pressure port closed

• Plunger piston is stationary, maintains reduced pressure in the right and left rear wheel circuits.

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Antilock Brake System For Early Subaru Part 2:

Antilock Brake System for Early Subarus:

ABS Service And Brake Bleeding Procedures:

Antilock Brake System for Early Subarus: The first Subaru rally car the Legacy RS relied upon the bousch/nippon ABS units to perform on the WRC circuit.
Antilock Brake System for Early Subarus: The first Subaru rally car the Legacy RS relied upon the bousch/nippon ABS units to perform on the WRC circuit.

Always check the fluid level of the master cylinder and bleed the wheel cylinders following the procedure listed in the service manual. When the HCU has been removed and/or replaced, the fluid must be drained. Replace the cone screws with bleed screws and attach a hose to drain fluid to a container.

Antilock: ABS Service And Brake Bleeding Procedures: A early Subaru Nippon ABS unit ECU.
Antilock: ABS Service And Brake Bleeding Procedures: A early Subaru Nippon ABS unit ECU.

Use extreme care when performing this procedure to prevent damage to the internal components of the HCU. Do not apply AV signal for more than 5 seconds for each application. If no AV signal is received, it is not necessary to close bleed screw between brake pedal applications.

Antilock Brake System Notes and Cautions:

The ECU on early Subaru ABS systems can only display one trouble code–the lowest numbered code. Correct the fault indicated by the trouble code and recheck ECU for another code. Repeat the self-diagnostic procedure listed above, and the next highest code will be displayed. Refer to the appropriate model year service manual for the trouble codes and corrective actions. While the ABS ECU is in the fault mode, the ABS will go to fail-safe and remain passive under all braking conditions. The brake system will function as a conventional power-assisted system without ABS.

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Antilock Brake System for Early Subaru Part 1:

Antilock Brake System for Early Subarus:

A variety of antilock brake system (ABS) have been installed in Subaru vehicles since the first systems were installed in the 1990 Legacy.  In the sections that follow, we’ll give you a brief overview of each system and explain proper diagnostic techniques.

Antilock Brake System for Early Subarus: A Subaru SVX ABS system.
Antilock Brake System for Early Subarus: A Subaru SVX ABS system.

Antilock Brake System for Early Subarus:

Early Subaru Antilock Brake Systems:

The original Subaru Legacy Antilock Brake System (ABS) was licensed by Bosch and manufactured by Nippon ABS, Ltd. The system electronically controls brake fluid pressure supplied to the brake system. This control helps to prevent “wheel lockup” during braking on slippery surfaces and emergency situations. The system includes a fail-safe feature, which indicates a malfunction by illuminating the warning lamp. The system is then returned to a conventional power brake system. The four channel system provides accurate individual wheelspeed control and improves the directional stability of the vehicle during braking.

Antilock Brake System (ABS) Components

• Tone wheels (4)

• Speed sensors (4)

• Electronic control unit (ECU)

• Hydraulic control unit (HCU)

• G sensor (manual transmission models)

• Warning lamp

A tone wheel is attached to each wheel hub and rotates at the same speed as the hub. The magnetic speed sensor is mounted in the axle housing. The notched tone wheel acts as a reluctor which modulates the magnetic field of the speed sensor. The tone wheels are individually replaceable.

The speed sensor provides an alternating voltage signal to the ECU. The alternating voltage and frequency corresponds to wheelspeed.

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WRX/STi rear wheel stud replacement

WRX/STi rear wheel stud replacement:

Careful cleaning of the threads/lugnuts and using hand tools (AKA NOT an impact gun!) will help prolong the life of your studs. When the day comes though, here’s how to replace the studs in the rear with stock length studs. If you want to replace them with longer length studs (ARP, etc.) you will have to pull the hub entirely and buy new wheel bearings.


Subaru 28365FE001 Wheel Stud

ARP 1007716 Wheel Stud Kit for Subaru

 

Things you will need:
Stock length wheel studs (As Required): NAPA has these for ~$3 a piece. Part # 641-3209
M8x1.25 bolts (2): Home Depot Racing
M8 washers (~6): Home Depot Racing
19mm Socket: Lugnuts
14mm Socket: Caliper bolts
12mm Wrench: ABS Sensor bolt
7mm Allen Key: M8x1.25 bolts
5mm Allen Key: ABS Ring bolts
Hammer: of the BFH variety, for beating on studs that have misbehaved
Telescoping Magnet Tool: Optional, but will make life much easier.

New wheel stud in the freezer.
New wheel stud in the freezer.

Sticking the new studs in the freezer will cause them to shrink slightly and really help you when it comes time to seat them in the hub. Throw them in the freezer before heading out to Home Depot Racing or leave ’em in overnight, just make sure those puppies are ice cold. Leave them in the freezer until you are actually ready to use them.

Remove the two bolts holding the caliper in place using your 14mm socket, and ziptie it out of the way. I have mine attached to the swaybar in this picture.
Remove the two bolts holding the caliper in place using your 14mm socket, and ziptie it out of the way. I have mine attached to the swaybar in this picture.
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