What does it mean if you suddenly lose braking pressure?

Never had this happen to me before. It's a 03 mazda b3000 pickup.

I was working last night which involves starting and driving my truck shortly, turning it off then repeating. And suddenly after starting it one time I find my brakes spongy and that I've got very low level of fluid in the MC. I dont have the truck on me, I left it at work and will ride my motorcycle to it today to work on it. I read somewhere it could have to do with some auto setting drum brake function that you can remedy by pumping the brakes while going in reverse, which I'll try first which would be great if it works, but if not would this most likely be some sort of failure somewhere in the system like a leak at some point that just suddenly busted? That's what I'd imagine although from a quick check with my phone camera(wasn't willing last night to wiggle my body under the truck) I didn't see any obvious fluid having leaked. I guess I'm hoping like the drum brake quick fix there might be something else(if not the drum brake system) that just fell out of order that won't require replacing any parts and I won't have to trap my tool box to my bike.

 

sounds like a leak somewhere would pump the brakes and see if you can find where its coming from brake lines can rust out , brake hoses sometimes go bad also, but also a caliper or wheel cylinder may be leaking.

 

Could be a lot of things but first look for a leak.Next bad master cylinder, wheel cylinders or calipers.

 

Check the brake fluid. Pump the brakes a few times. Check the level again.

 

Can you tell if its either a leak or air in the system somehow? I didn't see any leaks but I didn't get the closest look. Currently waiting for the rain to chill out.

How does this sound? I've filled the MC reservoir with fluid, pumped brakes, didn't drop.

https://youtu.be/DkKls23Tu_g

 

When was the last time you checked the brake fluid? If it's been a long long time and you can't find a leak, I'd just fill it up and monitor it. If the fluid level was full recently I would be concerned!

 

Brake fluid should never leak but will go down as the pads wear. Should never add brake fluid between brake jobs as the pad wear is calibrated to turn light on as pads wear. There is also a wear indicator on pads that will make noise when worn.

 

Where are you located?
After several years of cold winters, and lots of salt, I'd, guess a pinhole brake line leak.

Spring 3 years ago, a neighbor had to replace all the brakelines on his van, road sale put pinholes in all 4 lines.

Fall of that year, I had our #2 car up on ramps in anticipation for a long trip.
Had just finished checking or changing plugs/wires/filters/coolant/oil/windshield wipers & fluid/headlights/tranny/brake fluid.

Backed the car of the ramps, brake pedal went to the floor, and I saw two huge brake fluid puddles as I slowly coasted backwards down the driveway. (Emergency brake worked fine, after 5-seconds of "you've got to be kidding me" brake pumping...

 

brake system is a closed system.
If you loose pressure it is because
1) air got in the line
2) brake master cyl is toast (I'd put my money on this)
3) rupture or leak in the system, check brake lines

 

Found it

http://imgur.com/a/rZXT7qj

I've got the 2x4 but for some reason I need the 4x4 part to be the right fit. This last one, which is what the parts store will get you for my truck is too long and looks like it rubbed against the wheel. All fixed now