ABS/Bleeding/Leaking?

[hoyden]

Hi,

Replacing brake fluid, the front brake wasn't priming - so pumped the lever repeatedly before beginning the bleed cycle again - only this time a hissing sound (air escaping) started coming from the ABS unit.

Does anyone know if this is a pressure relief valve or if I've knackered the ABS unit? Or any insight as to what's gone on?

Cheers

 

[670cc]

What method was used for replacing the brake fluid? I’m unsure what you mean by “front brake wasn’t priming”.

 

[hoyden]

Hoses replaced.
New fluid was added.
Caliper bleed valve opened.
Brake lever applied.
Caliper bleed valve closed.
Brake lever released.
When the brake lever was just not getting any resistance pumped the lever a few times before opening the bleed valve. This is when the hissing of air from the ABS started.

 

[lootzyan]

...Caliper bleed valve opened.
Brake lever applied.
Caliper bleed valve closed.
Brake lever released.
When the brake lever was just not getting any resistance pumped the lever a few times before opening the bleed valve. This is when the hissing of air from the ABS started.

It is important to follow the sequence of the procedure when bleeding the brakes. Basically it is like this:
If necessary, add brake fluid. It is important that the piston in the master cylinder is always submerged.
Pump the lever or pedal several times
Hold the lever
Open (about 1 second) then close the bleed valve
Pump the lever
repeat as many times as needed
...
Of course, I assume that you have connected a clear vinyl hose to the bleeder screw, the end of which is immersed in, for example, a glass jar with brake fluid.
This way you observe whether the air is pushed out of the brake system and prevents air being drawn in.
If the power is not on, you certainly cannot hear the valves in the ABS module. The brake fluid flows freely through the ABS module.
If the master cylinder and the ABC module have been completely emptied, it may take quite a long time before you feel any resistance on the lever or brake pedal.
If you have little experience it usually takes two people to bleed the brakes.

 

[670cc]

If you replaced the brake lines you are going to have a lot of air in the system to purge.

 

[lootzyan]

You might find advice on the web to fill the master cylinder with brake fluid before attaching the main hose. If done carefully, it helps to fill the piston chamber with fluid so that there is less air. This makes it easier to bleed the brakes. But this is a very messy method. You need to cover corrosion-sensitive parts, e.g. with aluminum foil.