I’m trying to resolve a nagging brake problem on my 98 Pathfinder. In short, braking power is weaker than it should be, but I do not have sponginess in the brake pedal. I’ve bled the whole system a few times, and even changed the master cylinder - to no avail.
While performing a few tests lately, I noticed the following behavior: if I drive up a steep hill and start pumping the brake pedal with the left foot while keeping the right foot on the gas (to keep moving uphill), the pedal gets progressively harder to press and braking action diminishes accordingly. If feels a bit like when you switch the engine off with the car still moving (in neutral) and try to brake: as the vacuum in the booster gets expended, the pedal gets harder and braking action diminishes dramatically.
I don’t think this is related to the act of going uphill; it’s just that this is the only way the engine can develop enough vacuum for the symptom to occur.
This leads me to wonder if I have a vacuum leak somewhere (either in the line or in the booster itself) that only happens at higher vacuum pressures…