Thread: D2 ABS Modulator power bleed

The modulator bleed is exactly that, a modulator bleed. In order for the modulator to correctly sense and activate the calipers it needs to be clear.
Full pedal pressure opens the master cylinder circuit to the modulator supplying the pump with full available volume to purge any air.
Generally you need resistance on the outlet to limit the discharge so air pockets against the pressurised fluid and discharges thru to the lines without any surges.
Modulator solenoids and check valves will direct any air into the brake lines and hold it back. From here you can then bleed each wheel in turn.
The bleed tests are referring to bleeding a modulator that has been removed or replaced rather than a general bleed. If your just doing a quick bleed, keep nipples closed but you MUST put full pedal pressure on the pedal and hold it while it's running.
If, and I don't recommend it, you pull the relay and manually jump the pump, there is a timed process that it operates in. Just sticking in the wire and giving it 10 seconds will put you in the running for a new pump and an empty wallet. Pulsing it with the wire can also arc out the pump.

I don't mind lending a hand if anyone needs a Nanocom, however I reserve the right should people not take heed. Working with Wabco Truck systems everyday, I see a lot of workshops without the necessary equipment trying all sorts of shortcuts that end up in component failures putting someone's livelihood off the road for a few days. With most of my customers, that can be $20,000 on average per day lost.

Cheers

Andrew


Using Capitals, the difference between helping your Uncle Jack off a horse or helping your uncle jack off a horse...

Perfecto!

Thanks LMR

the explanation of how the air is expelled from the modulator without bleeding fluid from a pipe is a first. Extensive research of the net over the last few days has drawn a blank on that info being published elsewhere.

So now after having removed my modulator to do option B I will now bleed modulator with full pedal pressure, then power bleed the lines of the creamy stuff/bubbles.

Then repeat it till it's all clear.

Guess that's why it takes two workers about half an hour and 2 liters of fluid to complete the task

Thanks again you have filled in a hole in the info I reckon

Cheers and Beers

AL

This is the WABCO procedure for bleeding a dry ABS braking system. This looks close to the Nanocom modulator bleed information and to LMR's advice so should provide a basis for a useable procedure. The Wabco wet module bleed is essentially the same as the manual bleed procedure in RAVE.

Manual Bleed Procedure with Electronic Control Equipment

NOTE: The electronic control equipment must be capable of actuating (energizing) the outlet solenoid valves for each wheel for approximately 10 seconds and activating the pump of the modulator. The inlet solenoid valve should be open (de-energized). The Meritor WABCO Diagnostic Controller can be used to do this.

1. Apply the parking brake and chock the tires. Turn the ignition OFF.

NOTE: The ignition must remain off for the initial bleed procedure; energizing the unit during bleeding must be impossible.

2. Perform brake bleed procedure for wet module, bleeding the circuit and master cylinder if required prior to connecting electronic control equipment. Use Pressure Bleed Method if equipment is available; if not, use the Manual Bleed Method.

3. Install electronic control equipment to ECU, or to the modulator assembly and pump.

4. Turn ignition switch ON or power electronic control equipment.

5. Push on brake pedal with maximum force (firm pedal) and hold.

6. Activate the pulse function on the electronic control equipment starting with the longest brake circuit, typically the rear.

7. Release brake pedal for 5 seconds and activate the pump of the modulator for approximately 5 seconds.

8. Repeat Steps 5 through 7 three additional times.

9. Perform manual bleed on appropriate wheels.

NOTE: To perform a manual bleed, follow Steps 2 through 8 under “Manual Bleed Procedure (Wet Modulator Assembly)” on page 14.


10. Repeat Steps 5 through 9 for the remaining 2 [sic] brake actuators.

NOTE: If a firm brake pedal resistance is felt and the brake pedal pushes back when the solenoids and pump are simultaneously actuated for each brake circuit, the system bleed procedure is complete. If there is no firm pedal resistance, repeat the bleed procedure and/or look into brake system defect, (leaks, etc.).

So it would seem the whole process using Nanocom is something along the lines of:

1. Manual Bleed all wheels with ignition off (or Nanocom Power Bleed?)

2. Following RAVE bleed sequence (PF, DF, PR, DR) on each wheel
- run Nanocom ABS Modulator Bleed routine with pedal fully depressed, release pedal, repeat process 4 times
- bleed manually (or Nanocom Power Bleed?)
- move to next wheel in sequence

cheers
Paul

For completeness this is the Wabco wet bleed procedure:

Manual Bleed Procedure (Wet Modulator Assembly)
1. Apply the parking brake and chock the tires. Turn the ignition OFF and disconnect the battery terminals.
NOTE: The ignition must remain off for the entire bleed procedure; energizing the unit during bleeding must be impossible.
2. Fill the reservoir with DOT-approved hydraulic brake fluid.
3. Depress the brake pedal five times using the stroke between 1/3 travel and maximum travel in 5 seconds.
4. Release the pedal for 5 to 10 seconds. Air bubbles will rise into the reservoir while depressing and releasing pedal.
5. Repeat Steps 3 and 4 another three times, or until sufficient pedal resistance is felt.

6. Bleed the brake system. Put a wrench on the brake actuator bleeder fitting. Start with the farthest from the modulator, (typically the right rear), then attach a length of clear plastic tubing to the bleeder fitting. Make sure the tube fits snugly.
7. Submerge the tubing in a container of clean brake fluid. Figure 7.
NOTE: Both the tubing and container must be able to withstand to the effects of brake fluid.
8. Depress the brake pedal 10 to 15 times, using the maximum available stroke.
9. Loosen the bleeder fitting until the fluid begins to flow, (about 3/4 turn), while depressing the brake pedal through its maximum available stroke.
10. Tighten the fitting firmly prior to releasing the brake pedal.
11. Repeat Steps 6 through 8 several times until the discharged fluid is free of air bubbles.
12. Repeat Steps 3 through 9 to bleed the remaining three brake actuators. Bleed in sequence of the longest to the shortest circuit from the modulator.
13. Check the travel of the brake pedal. If a firm resistance is felt the manual bleeding procedure is complete.
14. Check the fluid level in reservoir and fill if required. Replace reservoir cap and dispose of used brake fluid.
15. Remove wheel chocks