Hi,

I have a 2003 Montero Sport 3.0L. Pads are good, fluid levels check out.

I am getting a hissing noise that is followed by the brake pedal hardening and the engine stumbling, almost loses stopping power.
I have to apply the brakes really hard to stop.
Doesn't do it consistently but about every other time I try to apply the brakes.

Any idea what might be going on?

Thanks

 

Faulty brake accumulator. It is a round 2.5-3" looking thing bolted onto the brake master cylinder. You have to replace it, otherwise you will be having not full braking power.
Easy job even for an inexperienced person. Make sure to have old rags placed below it when you do unscrew it, that way brake fluid does not eat your paint on the fender.