Night-Tracker

I've got an 87 4runner, it sat for a few months, didn't get much time to use it.
When I first drove it after letting it sit, I drove around town, about 20 miles. Everything went fine, next day, the brakes went spongy on the way home. Had to pump them to stop. Figured there was a fluid leak, but found no leakage and the reservoir is at the full line.

Then I noticed that the brakes work fine in park and neutral (yes it is an automatic).
I can even drive it down the street at 35mph, pop it into neutral and the brakes work normally, perfectly even. Although in drive, it will go to the floor in 3 seconds.

Any ideas?

the_supernerd

Something probably got corroded after sitting and damaged a brake piston. When you are in drive, there is more force turning the wheels, so you need more brake pressure. If you were to put it in neutral going down a hil, then the brakes would probably work the same as if you were in drive.

It does not take a big leak in the brake system to cause a soft pedal, meaning you do not need to see any fluid on the ground to have bad brakes. The master cylinder can leak between the pistons or into the brake booster and the rear wheel cylinders will leak into the dust boot when they go bad.

Check the rear wheel cylinders by pulling back the rubber boot on each side. If there is a lot of brake fluid in there then that is the problem. Check the calipers and the proportioning valve for leaks. If everthing else looks ok, then it is probably the master cylinder.