I have a 95 F Superduty 7.3 with an intermittent soft brake pedal. Just started noticing it last week, randomly when i stepped on the brake pedal it would feel alot softer than usual but i let up and the pedal would feel normal. However, today when driving around my yard it started doing it more frequently. Ive know there is a slight leak around the hydro boost area since I bought the rig, causing me to have to top off the master and power steering reservoirs every couple of months. Its not enough for there to ever be a puddle below it and no drips and never any lose of brakes or power steering, I would top them off when the whining noise would start when stepping on the pedal or turning the wheel.

My guess is the hydroboost as no lines or calipers are wet at all. Just looking for a second opinion before i spend the money. Other guess would be the ABS valve?

 

Sounds like you are on the right track. Have you changed the fluid recently? The only other thing I would think is that it might be worth changing the PS fluid fully to see if that helps. The added viscosity of new fluid might give you some additional life.

 

So apon further research I have realized what I thought was the hydroboost was actually the accumulator and that is the general area where I have fluid seepage. Degreased and power washed the area and had a buddy pump the brake while I looked for leaks and found nothing. I am going to take your advice on changing the fluid once I solve the leak

 

I dont have an F superduty so I know/think your setup is a little different then us 3/4 and 1 ton guys but I had a similar issue recently. I opened up both rear drms, one side was fine but needed new hardware and the other side was shot. A few springs were snapped and the pad assembly was able to sway back and forth. Fixed all that and good as new!

 

Yeah mine has disc's out back and there is no seepage at the calipers

 

so since this post I have flushed both the brake fluid and power steering, rebuilt the hydroboost with new seals and O rings, removed the ABS 20amp fuse, cleaned the rear load sensing brake proportioning valve and disconnected from the axle and obviously bleed brakes. Still have the same issue. Can pump the brakes with the ignition off then turn the key and pedal goes to the floor, not every time though. Im stumped. Being an F-superduty it doesnt have the rabs proportioning unit on the frame rail below the MC so i cant bypass it. Any thoughts or suggestions?

 

Well, I'm having similar issues on my truck (see signature). Shops are telling me it could be either the RABS (which you don't have) or the MC going bad.

 

After all my reading, I think that it has RABS but it is different than the 250 and 350 in that it is inside the MC, seems to be the best thing to try next, although I'm trying not to just throw money at it.