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Help with brake issue? Is it my booster or master cylinder?

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Hello all, I have a 1987 Toyota 4x4 Pickup with a 22r engine. I am having issues with the brakes and could use some advice on my next step.

I have been slowly restoring my neglected truck over the last few years. About 1 year ago I replaced the booster/master cylinder/rotors/drums/shoes/pads. Brakes were rock solid, best they have ever been. I was super happy.

About 2 months ago the engine would stutter when applying the brakes as if there was a vacuum leak. I serviced the check valve and it seemed to help for a few weeks. Then it started acting up again and I had a lot of brake pedal travel and stalled a couple times. I suspected the brake booster, so I removed and replaced it with a rebuilt unit under warranty. After dialing in the free play and bleeding the system 3 times it seems to drive fine on the road however:

  • The engine will still drop rpm's/stutter when I pump the brakes at a stop (never did this before).
  • The brake pedal will not get firmer when pumped and travels farther than expected.
  • The brake pedal goes to the floor if held while idling and feels somewhat softer than it should.
  • The check valve has been replaced, and is holding air. When check valve is pulled air can be heard escaping, it seems the booster and valve are holding air.
  • There are no other vacuum leaks near carb/engine
  • There are no visible leaks at the cylinders or master cylinders.

I am pretty confused at this point? Would a bad master cylinder cause these kind of issues? Or did I get a bad brake booster out of the box when I did an exchange?

I am wondering what my next step should be?
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What ever happened to your brake situation ? was it a problem with the Master Cylinder and did you replace it ?
I am having similar problems but I dont know if it is my Booster or my Master Cylinder with a 1985 1 ton pickup
and 22re engine.
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