I recently purchased a 1987 turbo 4runner for $1400. The owner had it sitting for 4years without starting it, I put a new battery in it and it starts and runs like new. Only problem are the brakes, after replacing the wheel MC and bleeding the brakes I noticed the brakes have good compression only when it's not running. When I have the truck running the brakes go all the way to the floor before stopping. I'm thinking it's a master cyl or the brake booster. Any suggestions or ideas on what the problem could be? I was told the turbo 4runners use a rarer dual diaphragm brake booster which runs a vacuum off the turbo.

 

It sounds like the booster is working if the brakes get really soft with vacuum assist. The pedal should be just about rock-hard with no vacuum, not feel like it does when driving.

 

Bump!

 

The booster is fine, are you sure you got all the air out of the system?

 

I agree with James - if it gets "softer" when you turn the truck on, the booster is doing its job. It sounds like a bleed problem, or possibly a stuck or poorly adjusted rear brake?

I recently replaced a bunch of brake parts on my '87 4Runner, and I could not bleed it - put 2 quarts of fluid through the system, didn't see any bubbles, but it just wouldn't firm up all the way. Spent $100 on shop labor to let them do it with their fancy tools, and it came back much firmer.