1995 Bonneville has brakes from hell...so this is a two part question but all have to do with braking system....
Went for a drive the other day and when I was ready to make a stop I applied the brakes and the car started to slow down and proceed to make my stop but all of a sudden the pedal just went to the floor...i released and reapplied the pedal but it was if had to pump the pedal to regain pressure....so that took place the whole ride home....worked over the past week on checking for leaks....one bad wheel cylinder.....replaced both rear cylinders shoes hardware and drums....bleed brakes same problem....decided to check front brakes and did the same procedure.....everything new under front brakes....bleed brakes....same problem....pedal to floor and have to pump to get pressure about out 2 times....replace master...bleed same problem...so i decided to replace proportion valves and brake booster....same problem......

Now when i start my car and if i apply the brakes you hear a hiss at the pedal as if there'* a leak...no fluid leaks and where and the car seems to change in idle as i apply brakes as if it wants to shut off.....do anyone have any input to what'* going on? And there are no vacuum leaks at booster under hood....PLEASE HELP!!!

It'* 8 AM and I'm under the car now!! Have to get to the bottom of this!

By chance is your car ABS equipped?

If he'* applying the brakes and its causing the engine to rough idle/die, then I suspect a leak at the booster. Probably on the back side of it where it mates to the firewall.

Didn't he say he replaced the booster with the M/C?

What about the hose to the booster, and the check valve on the end of it?

Yup, your right, he did say he replaced the booster.

How is the pressure of fluid when you are bleeding the brakes? Does it not start moving until the second pump, or do you get fluid coming out immediately?

Also, did you bench bleed the master cylinder while level outside of the car, before sticking it in there?
Were the brakes in the rear properly lubed and adjusted when everything went back together?
Are they still adjusted properly?
Where did the master cylinder come from, and was it new or remanufactured?

I think the booster just manages braking assistance, and has nothing to do with the actual creation of pressure. While it may be an issue, it may also fall right in line once the pressure issues are sorted out.

Thanks for chiming in guys...has great flow at each bleeder....I'm believing there'* air in the ABS Pump which may need to be bleed thru scanner....I'm going to replace the MC again...came from Autozone was new not reman...if that doesn't work I'm just send it to the shop...thanks agian will let you know what happens!