Very good!
Here's a quick list of where brake fluid can disappear to:
1) Rear drums: Leaking wheel cylinder seals. Some can be absorbed by brake dust. Larger leaks
will leak down the inside of the backing plate & drip onto inner wheel/tire sidewall/ground. Older trucks
usually have neglected rear brakes -- so majority of the time if you open up the rear brakes you will find evidence
of wheel cylinder weepage/seepage/leakage.
2) Front discs: Caliper puck seals. Brake fluid leaks end up on inside of wheels. Can be really hard
on paint, bad juju. Kinda rare to find in the wild because front brakes get serviced more regularly/swapped
out for sticky slides, frozen pucks, or other issues before the seals give out?
3) Rusty/weepy steel brake lines. Also sometimes the flexible rubber lines where the rubber is crimped to
the connections. Replace.
4) Master cylinder leaks into the cab, and goes *behind* the carpeting/rubber flooring. First place to
look IF there's no signs of external leaks in the 4 corners? Messy.
5) And if you've been adding a fair amount of brake fluid, and it's been disappearing with no trace?
Because you have a
JB5 setup, your power brake assist is developed by engine vacuum. If everything
fails just right, the brake fluid either get trapped inside the vacuum booster assy, or it actually gets sucked
into the intake manifold, gets burned, and disappears via the exhaust.
That pretty much covers the 5 areas you need to look for your disappearing brake fluid. Q: How often
are you having to add brake fluid, and what quantity?
Let us know what you find. Pictures when you catch it red-handed a plus!
And as always, brake issues should be addressed ASAP.
Happy Hunting --