Unusual Braking Issue?

[cam.man67]

I've never experienced anything like this before. The Scottsdale is optioned with heavy duty brakes and the vacuum assist looks like it comes off the power steering pump?

Anyways, the problem: at random times, the brakes are intermittently either working perfectly or my foot is all the way on the floor. The pedal travel is uneven, sometimes (maybe 1/2 the time) they grab when i just barely put on any pressure. Other times, not so much. I mean, the truck still stops regardless, but it's a little concerning to have your foot go all the way to the floor at random moments.

What could be causing this? My dad think it's air in the brake lines, but I'm not sure that's it.

[donut]

Ok, vacuum off the PS pump, probably not. However, Hydroboost does run off the hydraulic system.
Is this a recent problem?

Air in lines, possible, but how did it get there? Inspect all the brake lines, looking for wet spots. Also look at the drums and see if the bottom of the drums are wet, (wheel cylinder) or anything out of the ordinary on the calipers.
You could try bleeding, at least there will be fresh fluid in the lines.
Rule out the cheap stuff first.
Actually questioning master cylinder, but rule out the other stuff first.

[Sodell]

X2, if you check for fluid, and air in lines, and find none, I would bet it's the master cylinder.

[87 STEPPER]

It's more likely to be the actual Hydrobooster this is the component that is located between the fire wall and the master cylinder it is connected in series to the power steering pump and box and it is probably bypassing internally causing the problem you discribed.

Sometimes they will get so bad that if you try to brake and steer at the same time you will loose one and the other will overtake the pressure.

Just to be clear the Hydroboost system is not connected to the braking hydraulic system. It only assist in actuating the master cylinder piston.

[cam.man67]

Hmm. I'm not losing any brake fluid. At least, I haven't seen any wet areas. So...Hydroboost. Can I just remove it and hook the master straight up to the firewall? Or do I need to replace it?

[87 STEPPER]

I guess you could do that but I wouldn't reccomend it cuz then you would'nt have any power assist. I would take it to a known good brake shop and let them trouble shoot it for ya.

[cam.man67]

So the braking problem is still there, I figure I need to get this straightened out before it gets worse. What part number should I be looking for?

[donut]

Afaik, the part hasn't been identified yet...