Every Month or so, I lose my brake fluid, and then I have to re-fill the resevoir and wait for it to drain down to all the calipers. After abouta few hhours of driving, they return to full. What is the problem. It isn't leaking.

 

if your loosing fluid like that you must have a leak somewhere

 

yeah mine is doin this too, i cant find the leak.

 

More than likely, you have leaking wheel cylinder(s)or leaking caliper piston(s). The solution would be to rebuild them all.

 

Brake dust and grime will build up over the leak, making it very difficult to find. You must have a leak somewhere to cause the problem, be it a bad piston, wheel cylinder, or master cylinder.

 

Sounds like your master cylinder is going bad. Look right under it and if the paint under the master on the brake booster is bubbled up then that's what it is

 

They can sometimes leak into the car, also. Look up under the pedals and check for wet or bubbled paint in there, too.

 

How much fluid are you losing? The whole reservoir or a smaller amount? Are you also experiencing a loss of pedal when you are running low on brake fluid?

If you have a soft brake pedal and your master cylinder is near empty, you may have an issue with your brake master cylinder. The brake master cylinder can leak internally, so you may not see any outside evidence of a leak.

If you're not experiencing any pedal loss, your brake fluid reservoir isn't empty and there are no other signs of external leaks, you may be experiencing the normal phenomenen of hydrualics. As your brake pads and shoes wear down, more brake fluid is required to be transferred to the wheels in order for the pistons to make contact with the friction material.
It's normal to see the level in the reservoir drop down when this happens.