1997 7.3 xlt obs powerstroke
my brake light goes on and off, and my brakes come and go, sometimes rock hard and barely work sometimes work fine, bled the brakes and same thing, new master cylinder?

 

Sound like a vacuume pump is getting ready to lay down on you. The pump should pull at least 19 inches of vacuume.

 

Agreed, it might be a problem with the brake booster but it sounds like the vacuum pump.

 

so im new to psd, where is that located, how hard of a job, and how much $$

 

http://www.ebay.com/itm/NEW-OEM-Vacuum-pump-Ford-Powerstroke-96-02-7-3L-1996-2002-E250-E350-F250-/281335105871?pt=Motors_Car_Truck_Parts_Accessories&hash=item4180e1094f&vxp=mtr#ht_718wt_662It is on the front drivers side of the engine,by the air conditioner compressor, run by the serpinetine belt. Not to hard of a job, but you will need the pully puller that is designed for the pully that is used on the vacuum pump, and the power steering pump. And that same tool is used to install the pully on the new pump. You can't press or pound the pully on, as it will destroy the new pump.

 

I have borrowed the tool at a auto parts store a couple different times. When you start to put it back together, you have to put the bolts in the holes before putting the pulley back on.

 

I'm on my second cheapo from o'reilly. Both times it (the pump) went out, it seized. The first time I was almost home, and the serpentine belt seemed fine. The second time the belt was noticeably worn so I got to replace it along with the pump.