Bad brakes

Anders, you mentioned using a balance-bar system presumably with dual masters. Such systems can be used either with or without a vacuum booster. Do you use one? Vacuum boosters can fail their internal check-valves and lose their vacuum-boost capacity.
If pads glaze from hard use or lack of proper break-in, brake stopping power drops radically. Might be you simply need new pads or the old ones roughed up with scotch-brite or fine sandpaper, along with the rotor surfaces. Wilwood calipers usually come with their 'Polymatrix B' pads; I prefer Porterfield sports-racing pads for street Panteras.

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Wilwood calipers usually come with their 'Polymatrix B' pads

Wilwood Calipers do not come with any particular brake pad. Wilwood has a wide range of brake pads to suit the intended purpose of the vehicle. Polymatrix B pads are for racing only and should not be used on the street. The best pad for the street are BP10 pads IMO. They give a nice amount of grip without being too harsh on the rotors and without producing too much noise or dust. Most people will have their favorite racing pad and their favorite street pad. I use Polymatrix E pads for both street and track and couldn't be happier...

I have changed booster but the boosters piston seal was the thing I guess. But the vaccuum still is to low. The CNC master cylinders are sized to be assisted by a booster. The brake works fine during braking at the same time as down shifting and "engine braking". I have changed pads, now using a "green stuff", better for street use when the brakes aren't warmed up.
Still have low vaccuum during idle rpms.
Regards
Anders

I just had to change the external check valve on the outside of the can on the Pantera. It was stuck open.
Also on my 68 Shelby the original power brake booster finally failed.
I have it apart on the bench now and one of the diaphrams had dried out and split open.
Both of these items will cause issues of low vacuum.
The defective brake diaphram will make the engine vacuum drop to about 6 and not recover until you release the brake pedal. Sometimes it can make the car stall.

updates
Often there is troubleshooting and no information about how things went.

For info, I did install a vaccuum pump and the brake performance from the Wilwood's are back-
Thank you all

Anders

Yup. Same thing happened to me too. The vacuum pump fixed the issue.

Leaking 2 psi pressure residual valve.
The Pantera performance center deliver this valve in their Wilwood brake kit.
Whath will happend if they are removed?
Could the electric vaccuum pump give the brake booster that mutch power so it broke/blow the valve?

I do not have a residual pressure valve installed on my car. It is my understanding that the residual pressure valve is required when the master cylinder is mounted below the level of the calipers (street rod situation). This keeps the brake fluid from flowing back into the master cylinder thereby causing mushy brakes.

I'm sure others will chime in on this issue.

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Leaking 2 psi pressure residual valve.
The Pantera performance center deliver this valve in their Wilwood brake kit.
What will happen if they are removed?

Practically nothing. Try it and see for yourself. I routinely remove the valve(s) from all my cars. Some are built into the master cylinder and can cause much trouble if a second one like your Wilwood is added. The valve's intent is to keep a little pressure in the lines and the pads fractionally closer to the rotor for quicker brake response, benefitting sleepy drivers. It works OK for drum brakes (different valve, though) but IMHO you'll never notice approx. 0.002 second improvement in disc brake actuation time anywhere except a racetrack. Deleting the valve also slightly increases street pad life, lowers brake temperatures due to reduced drag, and on long trips you may even see a little mileage gain. Its also two less leak points in your system.