Replacing master cylinder - 95 Lumnina w/ anti-lock brakes

[davew9]

95 Lumina car, 3.1 engine, automatic transmission, Delco/Delphi ABS-IV anti-lock brakes. Haynes manual specifies that you must relieve tension on gears in abs unit using factory scan tool prior to removing master cylinder/abs unit assembly from car. Is there an alternate procedure for relieving the tension on the abs unit gears without a scan tool? If not, is there a low cost commercial scan tool that can perform this procedure? This car has the older OBD 1 diagnostic system. Any advice about this procedure or a link to a more complete description of the Delco/Delphi ABS-IV anti-lock brake system would be helpful. I've replaced master cylinders many times but never with this abs system. Thanks.

[maxwedge]

I just did this and had no issues, I bench bled the master and replaced it, I capped the lines on t from the m/c and got away with no system bleed, you may want to momentarily crack the bleeders on the abs before removing the m/c but even that may not be an issue. If you drain the entire the system then the scanner is required to bleed the abs. Mine was a 97 but I believe they are the same. *** Looking at some tech info it seems your system is unitized as the m/c abs unit this will need a high line scanner to unload the gears before removal.

[Blue Bowtie]

The Delco ABS-VI is the most owner friendly ABS system in existence. There are ways to bleed it and even perform some diagnostics without a scanner.

On initial ignition power-up, the fuel pump should cycle for about two seconds, but the ABS motor should also cycle briefly (and rather quietly). It's harder to hear the ABS motor run when starting the engine.

A few different scenarios may prevent the ABS motor from running:

• The lack of system power from the main relay will obviously stop the motor.
• A shorted or grounded wheel speed sensor circuit may stop the motor.
• An open or grounded brake pedal switch circuit can stop the motor.
• An open or grounded motor circuit or solenoid coil (or circuit) can set a fault code and prevent the motor from running.
• Some other hard fault codes in the EBCM can prevent motor running on power up.

SYSTEM POWER
There is a master ABS power relay and a pump motor relay in most installations. The main power relay is frequently located under the hood, inside the Underhood Electrical Center. (Older vehicles mounted the relay adjacent to the ABS hydraulic modulator unit.) The inside of the UEC cover should have a label indicating which relay is where. If you examine adjacent relays, you can often find another with the same part number and can swap them to see if that makes a difference. If the "other" device works but the ABS does not, chances are the relay was good. The EBCM operates the relay to provide main motor and solenoid power to the ABS modulator unit. One other check you can perform is to assure that battery voltage is present at the NO relay contact in the socket for the ABS relay. Obviously, lack of voltage there would interfere with ABS operation.

SENSOR INPUTS
Metering the sensors and wire harnesses at each wheel is easiest, and will reveal the condition of both the sensor signal level and wire harness. With the ignition off, you can check resistance to ground on the sensor harness wires to help reveal any cuts of other harness damage. With the ignition ON, and if the EBCM is powered, you should be able to measure a DC bias voltage across the two harness wires, but I'm not certain what that voltage is.

OTHER INPUTS
Check the fluid level switch, even of the red BRAKE warning lamp is not on. There are probably two sets of contacts in the switch, one N.O. and one N.C. to indicate switch position. The N.C. contacts are typically used to signal the EBCM whether fluid level is correct, and an open circuit here from a wiring problem or defective switch will not necessarily cause the red brake warning lamp to turn on.

Check the brake pedal arm switch for continuity. You may also want to insure that the center, high mounted brake lamp is working, since that can affect other systems on the vehicle, such as the cruise function and possibly the ABS.

OUTPUTS
There is at least one main valve solenoid on the ABS modulator unit, and up to six control valve solenoids. Disconnect the electrical connector and check the resistance of the solenoid coil windings one at a time , then the coil resistance to a good ground. The coils should present about 2-5 ohms through the coil, and show infinite resistance to ground. You can also test the solenoid coil wire harness for grounding if the ignition power is off.

There are many more checks which can be performed, but those get rather involved and nearly require a scanner.

MISCELLANEOUS PROBLEMS
Another, more obscure problem which can occur with this EBCM is a supply voltage problem caused by a failing alternator. If a rectifier in the alternator bridge is breaking down and allowing some reverse current flow, some AC voltage can be present in the system. Even relatively low levels of AC voltage can interfere with EBCM operation and inexplicably set error codes. You can test the output of the alternator directly at the output stud for AC voltage over 0.2VAC. At that level, problems can occur. Obviously, that is not likely the problem unless a hard code in EBCM history is causing the unit to shut down on power-up, since there should be nothing but clean DC voltage from the battery in a KOEO situation.

INDICATORS
Red BRAKE Warning Light -- With vehicle ignition on, Red warning indicator light indicates the following possible problems: low master cylinder reservoir fluid, parking brake switch closed or bulb test circuit closed, or that a problem exists in the basic braking system and the front/rear brake differential pressure switch is closed. If all conditions are normal the light will go off when the engine is started. The Red warning light is grounded through an EBCM or Light Driver Module circuit which will illuminate the light when one of the above conditions is present.

Amber ABS Warning Light - With ignition on, a flashing Amber ANTI-LOCK or ABS INOP light indicates a problem exists in the ABS system, but system is still operational. If light remains on steadily after the engine is started , it indicates a problem has affected ABS operation and no anti-lock braking will be available. As a self-test, the EBCM will turn on this light under certain conditions:

• The AMBER ANTI-LOCK or ABS INOP light will also illuminate for about 3 seconds when the ignition is first turned to the RUN position.
• This AMBER light also remains on while the ignition is in the crank position.
• Finally, this AMBER light will remain on for about 3 seconds after the engine starts, then will go out as the ABS system performs a self test.

Amber LOW TRAC Warning Light (some vehicles)-- With ignition on, a Amber LOW TRAC light comes on as a bulb check. Light will come on during ABS operation warning driver of slippery road conditions. Light will stay on for about 4 seconds after ABS system stops operating.

BLEEDING THE BRAKE SYSTEM
NOTE:

Before bleeding the brake system, the front and rear modulator pistons must be returned to the topmost position. The preferred method is using a TECH-1 scan tool. If this tool is not available, an alternate method can be used.

Brake Bleeding with Scan Tool - If using a TECH-1 or other ABS capable scan tool to position piston, scanner and enter manual control function. Ensure enable relay is on and apply rear motor. On later versions of the TECH-1, use the Motor Rehome function of the scan tool. Pistons should return to upper position. System is now ready for pressure or manual bleeding.

Brake Bleeding Without Scan Tool -

1. If a TECH-1 scanner is not available, use this alternate method. This procedure will only work if the AMBER warning light is not on and no trouble codes are set. Repair any system defects before proceeding.
2. Remove foot from brake pedal. Start engine and allow to run for at least 10 seconds. Ensure AMBER ABS warning light is off after 4 seconds. Turn ignition off.
3. Repeat steps 1) and 2) one more time. System is now ready to be bled using pressure or manual bleeding.

PRESSURE BLEEDING
CAUTION:

Use only DOT 3 brake fluid from a sealed container. DO NOT use DOT 5 silicone brake fluid. This is a generic bleeding procedure. ALWAYS use the bleeding procedure for specific year, make, and model vehicle that is being serviced.

Bleeding Brake Control Assembly (With Integral Master Cylinder) -

1. Clean master cylinder reservoir cover and surrounding area. Ensure reservoir is full. Attach a bleeding adapter and equipment to the master cylinder reservoir. Pressurize the system to psi (.7 kg/cm2) for 30 seconds.
2. Slowly increase the pressure to 35 psi (2.5 kg/cm2). Attach a clear bleeder hose to the rear bleeder valve on the hydraulic modulator. Submerge the other end in a container of clear brake fluid. Slowly open brake control assembly rear bleeder. Allow the fluid to flow until no air is seen in the hose. Close valve and repeat procedure for front bleeder valve on hydraulic modulator.
3. To bleed modulator unit brake line connections, position shop towel below brake pipes. Using flare wrench, slightly open forward brake line fitting at modulator assembly. Allow air to escape and tighten fitting. Repeat this step at remaining 3 brake line fittings, moving from front to rear.
4. If pedal feels soft or spongy, connect the TECH-1 scan tool. Use the TECH-1 to apply and release each modulator motor at least 2-3 times, and cycle each solenoid 5-10 times. When done, be sure to "Apply" front and rear modulator pistons to ensure they are in the topmost position.

Bleeding Wheel Brakes -

1. Ensure master cylinder is full. Raise and support vehicle. Attach bleeder hose to right rear bleeder valve and submerge other end in clean container of brake fluid. Open bleeder valve and allow fluid to flow until no air is seen.
2. Tap lightly on wheel cylinder/caliper housing to free trapped air. Close valve and repeat procedure for remaining wheels: left rear, right front and left front.
3. Do not drive vehicle. Remove foot from brake pedal. Start engine and allow to run at least 10 seconds. Turn ignition off. Repeat step 3) at least 5 times.
   
4. Test drive vehicle. If necessary, repeat bleeding procedure.

MANUAL BLEEDING
CAUTION:

Use only DOT 3 brake fluid from a sealed container. DO NOT use DOT 5 silicone brake fluid. This is a generic bleeding procedure. ALWAYS use the bleeding procedure for specific year, make, and model vehicle that is being serviced.

Bleeding Brake Control Assembly - Verify reservoir is full. Attach a clear length of hose to the rear bleeder valve and submerge the other end in a container of clean brake fluid. Slowly open rear bleeder. Apply brake pedal until fluid begins to flow. Close valve and release brake pedal. Repeat procedure for front bleeder valve.

Bleeding Wheel Brakes-

1. Clean master cylinder cover and surrounding area. Ensure reservoir is full. Raise and support vehicle. Attach clear bleeder hose to right rear bleeder valve and submerge other end in container of brake fluid.
2. Open the bleeder valve. Slowly depress the brake pedal. Close the bleeder valve and release the brake pedal. Repeat this procedure until no air is seen in the hose. Repeat the procedure for the left rear, right front and left front valve. Ensure reservoir is full.

[maxwedge]

Great info, I was too pressed for time to go to these details, the issue always arises if the system winds up empty, most time I have been unsuccessful with the manual method.

[davew9]

Yes, great info. I manually bled the brakes and the red brake warning light is off and the brakes tested fine, although I did not test the ABS system and the amber ABS warning light remains on. I'll perform some of the other checks you listed and repost. I really appreciate the info you provided.

[bmcpeters33]

hi just wanted to know what tools are needed to replace the master cylinder on a 96 chevy lumina?

[bmcpeters33]

yes but i dont know what tools to buy??? a wrench? a screwdriver?

[Schurkey]

Originally Posted by bmcpeters33

yes but i dont know what tools to buy??? a wrench? a screwdriver?

I'd suggest starting with a service manual from eBay. Often around $30 shipped. I bought one for Dad's '98 and I think it was less than $30 shipped.