No rear brake again

[Martynbradley]

When I bleed the brake it take at 4 of 5 pumps of rear brake to get air out, that to me suggest air is up by the modulator and when air comes though its a lot.
In my opinion air is being drawn into system when the bike is stood for a long time and I think it could be aluminium washers used on the bangos to the modulator.Why the didn't use copper washers as this is the prefered for bangos as they create a better seal.
Also could it be not that they didn't torque bango bolts on modulator properly on some bikes ?

 

[RUN666]

Anything is possible, really! Since I'm still unsure of the real cause of this problem, I'll wait and see if what I did changed anything. If not, then I'll really look for the source of the problem: loose washers (that'll be easy to check...), overheating around the ABS unit... or some other nonsense!

In the meantime... I'm driving!

 

[atomsplitter]

The only way to get air into a 'sealed' system is if the system is under vacuum. That means if the system is below atmospheric pressure it can draw air in thru sealing surfaces, however if that were the case, under pressure it would leak fluid out unless the banjo is acting like a check valve (it doesn't). When the system is filled and vented (purged) it should be at atmospheric pressure since the reservoir cap is removed to add the fluid. If you're getting 'lots' of air out then there is something else going on like inadequate purging. If you're using a vacuum pump to draw fluid from the reservoir (most power bleeders) you may be moving air around the system. The ABS module only bypasses fluid back to the reservoir (i.e. lower caliper fluid pressure) in pulses so the tires don't lock up. The ABS modulator doesn't do anything if the speed sensors aren't calling for activation.