Odd Brake issues

[Wobbiest]

93 FJ80, stock brake system

If I jam the brakes the truck stops pretty darn well for its size. I cant really get ABS to kick in even on a slam the pedal down stop, but i cant complain about... BUT

There are some come and go things that are starting to freak me out a little.

-Sometimes for no reason I'll stab the brakes and the truck acts like brakes are more of a suggestion than anything.
-Sometimes this happens while transitioning from throttle to brakes quickly which makes me think it has to do with vacuum
-Sometimes it is not from an abrupt change though, just randomly will not brake AT ALL like it normal does. I'd say in the course of a day of driving it will do it once a day.

Any thoughts? I mean I can do panic stop after panic stop and it will haul the thing down like I dropped an anchor and every once and a while its like mehhhhhhhh, maybe I'll stop.

 

[ppc]

You've used a lot of adjectives that don’t describe what is happening. Is the peddle soft and spongy or does the peddle go to the floor? Do you need to pump the brakes? What speeds are you experiencing these symptoms?

 

[Wobbiest]

I'll use more adjectives to explain how I want your supercharger...wait maybe those are adverbs....

Sorry to leave that out, no spongey, solid pedal almost not enough give. Im very used to non power brakes, but its not that feeling. Its more like I couldnt give it enough pressure if I had a jack there. PEdal stays high and quite firm. Pumping brakes does nothing. Experienced it all speeds from 25 miles to 80mph. Once or twice at 25mph it kicked the ABS on too.

 

[ppc]

Hard pedal is related to the brake booster. Check for vacuum leaks in the hose going to the booster and also the inline check valve as the first step. After that check all other vacuum lines and connections.

Have you done any recent maintenance where you may have moved or bumped the vacuum lines.

 

[Wobbiest]

Already been down that route I replaced the booster hose and I see/hear/feel no vacuum leaks.

But its not hard pedal like a bad booster where its just increased pressure. Its a firm pedal like the fluid doesnt want to make it to the calipers. The pedal stays higher and even slammed as hard as I can go, it just generally slows. I have manual 4 wheel drum classics that will stop on a dime with the pedal mashed and some decent modulation. This is sketchier and more random. 1 out of a 100 pedal presses lets say.

But the check valve. Good call. thanks