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Disco2 Brake bleed problem


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Help needed. I have replaced the ABS Modulator on my 1999 Disc 2 Td5 and carried out the shuttle valve mod. I have a Lynx diagnostic tool which I am using to power bleed it. I have bled the ABS modulator several times and started bleeding the wheels in the correct sequence. The first 2 wheels (LF and RR) bled without any problems but I can't get the other 2 wheels to bleed at all.

Looking at a schematic for the modulator it looks as though there are 2 separate channels through the modulator with LF and RR callipers being on one channel and RF and LR being on the other.

Has anyone any suggestions on what the problem could be please and how to overcome it?

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A modulator bleed can be a tricky operation, it requires resistance at the outlets (closed nipples) and full brake pedal pressure to open the master cylinder circuit. The internal valves of the modulator will expel the air into the wheel lines. I am not familiar with the Lynx unit and whether it has a modulator specific  bleed operation?

If the Lynx is just power bleeding then be careful not to run the pump too much at a time.  Is this a used replacement? was it carefully removed and ports capped?

 

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You can bleed D2 brakes to a sufficiently ok level without a power bleed, so I’d do this first. Once you have all four corners done, then power bleed to firm up the pedal to the correct level.

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On 6/6/2021 at 12:14 PM, Blanco said:

A modulator bleed can be a tricky operation, it requires resistance at the outlets (closed nipples) and full brake pedal pressure to open the master cylinder circuit. The internal valves of the modulator will expel the air into the wheel lines. I am not familiar with the Lynx unit and whether it has a modulator specific  bleed operation?

If the Lynx is just power bleeding then be careful not to run the pump too much at a time.  Is this a used replacement? was it carefully removed and ports capped?

 

The Britpart Lynx is a full diagnostic device. It will bleed the ABS modulator as well as each brake line individually.

 

On 6/6/2021 at 7:18 PM, Pawl12 said:

If you didn't change the ABS modulator or do anything that could have caused air in it, you only need to do a normal bleed.

I have changed the ABS modulator.

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Best to bleed at the wheels manually, or at least check after using diagnostics.

Why did you replace the modulator? Could there have been another fault that is still present and now causing the bleed problems? You are correct there are 2 totally separate circuits, from the master on. So you can undo the lines coming from the master at the modulator to verify you have equal flow in both. We had a similar problem a while ago, only one system operational. I ended up taking the (new) master off the booster and carefully refitting and everything was fine. Never found out the the actual cause, misalgnement of the actuating rod seems most likely.

Filip

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