I have an '89 Toyota Pickup and love her, so brakes feel good when running to the store and back and shorter drives, but after a while I notice that if stopped at a stop light for long enough the brake pedal slowly loses pressure and eventually goes to the floor, if i pump it the pressure comes back but gets worse, wondering if you more experienced users could tell me from your wisdom what this most likely is. I'm wondering if it's air in the brake line or not enough fluid, but I am a novice, pretty much just an oil changer haha! Thanks in advance!

-Ryan

 

I assume fluid level in brake master is ok.
Pull the wheels and check calipers and rear wheel cylinders for leaks. On the rear wheel cylinders you usually have to pull the dust boots back to check for leaks. If fluid pours out the boots the cylinders need to be replaced.
Assuming no leaks you can try bleeding the system. Don't forget to bleed the LSPV.
If after all this you still have issues than the brake master cylinder could be faulty. Sometimes they leak externally, but they can often develop internal leaks. Aisin offers a master cylinder at a very reasonable price. same with wheel cylinders.
If you do find any leaks at front or back., and the pads and/or shoes got wet, you'll need to replace those, too.
My thoughts. let's see what others suggest.

 

sounds good to me. If I may amplify Jinkola's information a little:

Bleeding the brakes is done in a specific order. Passenger rear, driver's rear, passenger's front, driver's front, LSPV. Notice it follows a pattern, from farthest from the Master Cylinder to the nearest.
I've found that pulling the actuator bar for the LSPV off the axle and running it through it's entire range a few times before bleeding the LSPV tends to help break up all the crud that builds up in it. Then, when you bleed it, it all flushes out much more easily. If it doesn't work, you'll need to tear the LSPV apart to clean it out.

If you do change out the Master Cylinder, don't forget to set the pedal height etc. A mis-set brake pedal adjustment could account for your troubles. If the bar that the pedal pushes on is out of adjustment, it could be allowing the brake fluid to bleed pressure off while you hold the pedal. Alternatively, the plunger inside the MC may have old, leaky, o=rings, allowing pressure to bleed off while you hold the pedal. Replacing to MC is actually pretty easy.

Another possibility for "wet" brake shoes in the back is a leak in the axle seals. This can often be caused by a clogged up breather on the rear pumpkin. It's super easy to pull off to check, and/or clean out. Keep a sharp eye on that. Your rear brake shoes get wet with oil, they MUST be replaced I hate working drum brakes. They're a PITA...

Ok, OK, shutting up now...
Pat☺

 

Agree with Jimkola. If there are no leaks, then 100% bleed all the old fluid out the lines/system and add new. Who knows how old that fluid is.

"Glycol-ether (DOT 3, 4, arnd 5.1) brake fluid is hygroscopic, meaning that it absorbs moisture from the air over time. This moisture can affect a braking system in a number of ways. As more water enters the brake fluid, the boiling point is reduced. This is a problem as the water can vaporize in the braking system, causing an air void, resulting in a 'soft' or 'spongy' brake pedal and reduced braking efficiency."

If it still exists then the Master cylinder seals may be bad allow fluid to pass by. Installing a new Aisin master cylinder is my next step. They are inexpensive and easy to install. I would PB Blaster penetration spray all the brake line to master cylinder connections and let it sit over night. Taking those off even with the tool always scares me.