Thread: D2 ABS Modulator power bleed

Ive just bleed as normal, than done the power bleed with bleed nipples closed. If you replace fluid regularly it shouldn't matter. 40,000 ks I think.

Not sure that answers my question?

From what I remember of a previous thread.

To flush, you bleed with nipples open and have a long tein core wire and switch to turn the pump on/off. turn on and open watch for clean fluid. Also requires someone to watch the reservoir and top it up as required.

Zedit: Thread here; http://www.aulro.com/afvb/discovery-...-quantity.html

Involves jumping the relay.

Thanks yep, read all that. Seems everyone power bleeds the modulator by opening the wheel nipples BUT,

still the question , why does nano com instruction for a modulator power bleed specify "all pipes closed and full pressure on the pedal" while running the pump?

Is the modulator purged of air even when the pipes are closed? I.e you don't have to release the fluid at the nipples for a nano com modulator power bleed? And then after that you do a ABS power bleed at each wheel to purge the lines as the modulator bleed has purged air from modulator into the lines?

Just trying to get the logic of the nano com method right?

Maybe I should contact BBS?

Cheers

AL

Hi AL

Maybe you'd get a definitive answer from BBS support. I'd certainly be interested in knowing the answer.

I've tried to piece together what each bleed does from available information:

The BBS help pages for the WABCO SLABS module don't appear to give a procedure for bleeding but make a distinction between the ABS power bleed which "opens all of the ABS valves" and the ABS modulator bleed which "opens the abs modulator valve". The Nanocom One indicates the power bleed activates the primary ABS circuit, while the modulator bleed activates the modulator ABS circuit.

RAVE lists three operation modes for the ABS module - Normal Braking Mode, ABS Braking Mode, and Active Braking Mode:

Normal braking mode
When the brake pedal is pressed, pressurised fluid from the master cylinder assembly moves the shuttle valves to
open lines 'A' and close the shuttle valve switches. Pressurised fluid then flows through the open inlet solenoid valves
to operate the brakes. The closed shuttle valve switches supply a brakes on signal to the SLABS ECU. If the SLABS
ECU determines that EBD is necessary, it energises the inlet solenoid valves for the brakes of one axle. The inlet
solenoid valves close to isolate the brakes from any further increase in hydraulic pressure.

ABS braking mode
When in the normal braking mode, if the SLABS ECU determines that ABS braking is necessary, it energises the inlet
and outlet solenoid valves of the related brake and starts the return pump. The inlet solenoid valve closes to isolate
the brake from pressurised fluid; the outlet solenoid valve opens to release pressure from the brake into the expansion
chamber and the return pump circuit. The brake releases and the wheel begins to accelerate. The SLABS ECU then
operates the inlet and outlet solenoid valves to control the supply of hydraulic pressure to the brake and apply the
maximum braking effort (for the available traction) without locking the wheel.

Active braking mode
When ETC or HDC are enabled, and the SLABS ECU determines that active braking is necessary, it starts the return
pump. Hydraulic fluid, drawn from the reservoirs through the master cylinder, shuttle valves and lines 'B', is
pressurised by the return pump and supplied to lines 'A'. The SLABS ECU then operates the inlet and outlet solenoid
valves to control the supply of hydraulic pressure to the individual brakes and slow the wheel(s).

This seems to suggest that Power Bleed only effects the portion of the circuit used by Normal and ABS Braking (Circuit A). The Modulator Bleed looks like it is required to bleed Circuit B used by ETC and HDC.

The rationale for the Nanocom bleed procedure could be that you use the Modulator Bleed to move air and fluid from Circuit B into the main braking system, and the Power Bleed to remove air/fluid from the main braking system?

cheers
Paul

Seems that the "closed circuit" bleed moves potential air around inside the ABS block into the lines to the calipers (unless it goes to the line from the reservoir and relies on gravity bleed, but unlikely), but then it'll still need to be bled to the wheels.

That was my guess at the logic as well but from the schematic it's not obvious to me how the modulator bleed would purge the B system of air into the A system without opening any nipples at the calipers.

After my option b job I did a modulator power bleed as per nano i.e without opening any nipples, (run the function numerous times) and then did the old manual bleed at each wheel.
This produced a "coffee crema" like froth initially which eventually ran clear. Used up just two small bottles of castrol dot 4 and things feel fine and all ops normal.

I will send a question to BBS asking to explain the nano manuals instructions and report back. I've searched hi and lo for the last two days and no other definitive info found.

Thanks chaps

Here is my question to BBS regarding the correct procedure for a modulator power bleed via nanocom evolution

" Being a recent purchase from yourselves and not that familiar with the system I have a question regarding the user manual notes for use of the ABS diagnostics and test facility.>

>For a Modulator power bleed the user notes mention "all pipes closed
> and pedal fully depressed" during the activation of the power bleed.
> does this method give effect to purging the modulator of air without
> the need to open the bleed nipples at each wheel? how is this
> achieved? or do you need to bleed fluid at the wheels while the modulator power bleed is cycling to purge the modulator of air.
>
> thanking you
> Allan Pickering

Response From BBS

Good morning Allan

With reference to your email I am afraid we are only the suppliers of diagnostic equipment and do not work on vehicles for a living therefore we cannot advise on the procedures for doing such work.

The equipment is provided to customers who wish to do work on their vehicles and gives them the tools to do so but we cannot advise on actual procedures as this is not something we do.

The workshop manual should explain the procedure for doing such work as you are describing with the Nanocom actually just allowing the procedure to be carried out more easily.

I am sorry we cannot assist further with this but the support we give is purely for issues with the hardware and should any issues with the software be found.

Kind Regards

Ron Blakey

So no help there regards the details of using nanocom to power bleed the modulator

RAVE says

"Bleeding of the brake system can be carried out
using the procedures given on TestBook, or by
following the manual procedure given below.
WARNING: If the ABS modulator has been
replaced, the brake system must be bled using
the procedure on TestBook, to ensure that all air
is expelled from the new modulator."

Can anyone quote the testbook modultor bleed procedure?

Hmmmm the search for a definitve answer continues!