Where is the brake booster located on a 97 Mercury 4.6 v8

If you are referring to the brake power booster, after you remove the master cylinder there are 4 nuts holding the booster accessed front under the dash behind the top of the brake pedal/

Hi, your basic symptoms will be. Your brake pedal. Will be very hard to push. When the pedal is engaged there will be a large vacuum leak, usually causing the engine to be very ruff or stall. If its bad enuff, youll hear the the air leak when pedal is depressed, hope that helps.

If you remove the master cylinder first there is

12 specific steps will help you :
1 With the engine off, step on the brake pedal several times to relieve the brake booster of vacuum.
2 Press the brake pedal down and start the engine. Verify that the brake pedal sinks slightly. Turn off engine.
3 Remove the vacuum hose from the brake booster.
4 Remove the brake lines from the master cylinder. Remove the master cylinder from the brake booster. Plug the fittings to prevent brake fluid seepage.
5 Disconnect the brake pedal from the push rod.
6 Have an assistant hold the brake booster from inside the engine compartment. Remove the nuts that hold the brake booster to the firewall. These nuts are usually located under the dash on the interior of the firewall.
7 Remove the brake booster.
8 Install the new brake booster to the firewall. Tighten the mounting nuts.
9 Connect the push rod to the brake pedal.
10 Connect the vacuum hose to the vacuum brake booster.
11 Attach the master cylinder to the new brake booster and reconnect the brake lines.
.12 Bleed the brakes at the master cylinder.

I never ran into one either in 50 years

How about the booster replacement &
the adjustment ,if any, on the rod to master

May not actually be pushing enough fluid to
the proper pressure

Usually I would say you had no helper in the
bleeding process, but you say many,many & never,

Rubber brake hoses collapsed inside ?

On the firewall mounted on the brake booster,the booster is round,,almost like a puffed up pancake,

1. Step 1 Mark the brake lines coming into and out of the master cylinder using masking tape and permanent marker.
   
2. Step 2 Orient the tube wrench so that it grabs the end of the nut by first sliding it over the brake line.
   
3. Step 3 Pull the brake lines out of the master cylinder.
   
4. Step 4 Unbolt the two bolts that hold the master cylinder to the brake booster.
   
5. Step 5 Slide the master cylinder off the brake booster.
   
6. Step 6 Remove the bolts that hold the brake booster to the firewall.
   
7. Step 7 Remove the cotter pin from the pin holding the back of the brake pedal to the master cylinder.
   
8. Step 8 Slide the brake booster to brake pedal pin out of the mounting bracket.
   
9. Step 9 Pull the brake booster off the firewall.
   
10. Step 10 Install the new brake booster. Installation is the reverse of removal.
    

the PCV valve is is typically located in the valve cover near the brake booster-4.0L pushrod V6. On a 5.0L V8 engines, the PCV valve is located at the back of the intake manifold.

Look by your air filter duct...refer to this picture:

Make sure your brake light are functioning properly. Some CC use the brake light circuit to release. If there is a bad bulb cruise won't work.