Tektro Draco hydraulic disc brake not gripping rotor well enough to stop I have two Motobecane commuter bikes with Tektro Draco hydraulic brakes. For several years we lived an apartment where the bikes had to hang vertically on a wall which would cause the brakes (particularly the rear ones), to become spongy and have little pressure. Usually taking them off the wall and pumping the brakes several times would create pressure in the brakes such that they would work again and there would be less play in the brake lever. They would typically be fine until they were put back on the wall.

Anyway, have since moved and the bikes are stored level. Started doing maintenance as I want to learn how to maintain my own bikes, particularly the hydraulic brakes. 

I gather the last thing that should be done to resolve issues is to bleed the system, so I'm trying to trouble shoot the system. One bike had a ton of play in the brake lever and it would almost touch the handle bar. That was easily fixed by adjusting the screw behind the lever.

The other bike is the one I am having trouble resolving. Basically, the rear brake caliper isn't grabbing the rotor well enough to stop, especially when a +170lbs person is on it. Here are somethings I tired:


The lever was getting pretty close to the handlebar, so figured adjusting that might help, still nothing.
Pumping the brakes no longer works as far as what I perceive to be building up pressure in the brake line.
Check the brake rotor and pads for contamination. The rotor seems fine as there isn't a film on it or anything. The pads were pretty dirty, almost black, and were smooth. Figured that was the issue. Took sand paper to them and still not gripping the rotor well enough to stop.
I've ordered new brake pads which haven't arrived yet and will try to put those on. Tektro says to replace them if &lt;0.5mm. I'd say they still have around 2mm on them. If that is the issue though, it seems like it would mean the calipers aren't getting close enough to one another to grab the rotor, right?
If that is the case, what is the next step? Adding more mineral oil to the system and bleeding it, or is there a way to adjust the calipers so that they are closer to one another when compressed?
As the comment by @Chris H, pointed out, you may have some air in your system. This is easely solvable by bleeding the brakes. Dependening on the design, you may need a big syringe, small hose(ideally translucent) and a small discardable bottle, or a propietary bleeding kit. Hydraulic system needs to be bleeded at least once a years, IMO.

WARNING: Never mix mineral oil with DOT, those are incompatible. You must choose properly your fluid Dot or Mineral Oil. Mixing DOT5 with DOT6, is fine, not recommended but fine.

Check the fittings on the handle and the caliper, tight them if needed. Some air may be getting into the system due to loose fittings. Also check the bleeding valves too.

Lastly, check the hydraulic lines while you pump the lever. If they seem to stretch, wide, or inflate a small ballon, etc. You will need to replace them.