Rear brake lost all pressure

[Albike]

The SRAM db8 rear brake on my Fezzari has been slowly losing hydraulic pressure over the past few weeks and today there was no pressure at all. Lever goes right to the handlebar with no brake force at all.
I realize that this would indicate a loss of fluid and air now in the system.
I see no sign of fluid leakage and no obvious external damage to the components.
Any advice on what and how to check the system.
I have a sram bleeder kit on the way but will have to discover the source of the problem first to be sure that it won’t continue to happen.

 

[fooferdoggie]

The SRAM db8 rear brake on my Fezzari has been slowly losing hydraulic pressure over the past few weeks and today there was no pressure at all. Lever goes right to the handlebar with no brake force at all.
I realize that this would indicate a loss of fluid and air now in the system.
I see no sign of fluid leakage and no obvious external damage to the components.
Any advice on what and how to check the system.
I have a sram bleeder kit on the way but will have to discover the source of the problem first to be sure that it won’t continue to happen.

it could just be contamination too. overheating will cause it too. Sometimes flipping the bike over will too.

 

[il Munduato]

The SRAM db8 rear brake on my Fezzari has been slowly losing hydraulic pressure over the past few weeks and today there was no pressure at all. Lever goes right to the handlebar with no brake force at all.
I realize that this would indicate a loss of fluid and air now in the system.
I see no sign of fluid leakage and no obvious external damage to the components.
Any advice on what and how to check the system.
I have a sram bleeder kit on the way but will have to discover the source of the problem first to be sure that it won’t continue to happen.

Somewhat common on the rear brake, especially if not bled properly at install.
I would do a "Lever Bleed" first as it most likely just needs to be topped off.

Here's another video.. pretty standard process across manufacture.

Raising the front of the bike and tapping the brake line can help for stubborn bubbles. As well as removing the caliper and letting it dangle low.
Just imagine an easy path for air bubbles to escape

 

[Albike]

If I pump the lever quickly and many times rear brake does come back but loses the pressure if I stop pumping