I am missing all of my brake fluid and I have no idea where it went. The pedal got sponge, I checked the resevoir and discovered that it was emty, or atleast so low that I could not see any fluid from outside the resevoir. I added fluid and it seems to be hold the fluid but the pedal is still spongy. There is no fluid on the ground under the truck. The backing plates look dry from the outside and the from calipers are both dry as well. the pads are about 20% worn and the brake lines are all dry. Any suggestions would be great. Thanks.

 

Check ALL the pads/shoes, You may have worn the inboard pads a lot more if the calipers arent sliding freely. Also look at the line on the drivers side behind the fuel tank going to the rear axle. they have a tendency to rot out there.
Once air has entered the system it must be bled out.

 

Any grinding noises? If either the rear shoes lost their lining or the front pads lost theirs, you would have a situation where there would be a pretty large demand for fluid but no leak, and the brakes would appear spongy.

 

I do not have any fluid on the ground so I do not think the lines are bad. However it is still dark here. No grinding of any kind. The pads and calipers are all less that a year old and have less that 20,000 miles. I will take the drums off later today and get back with you when I learn more. thanks for the suggestions.

 

When was the last time you removed the cap and actually looked inside the reservoir?