I know, you read the title of this post and OBVIOUSLY it's the master cylinder.

That is what I think as well, but PRIOR to spending the 650.00 on the replacement, how, what steps can I do, walk thru to ensure it's the master cylinder?

Here is what is happening;

First, my wife says it only happens when it rains, when I ask "what is it thats happening", she replies with, "the pedal just goes all the way to the floor and the car starts moving!!! FIX IT!!!"....

So I've been driving it for two weeks and today, for the first time, I found a series of steps to duplicate her report.

1 - your in drive and completely stopped, like at a red light
2 - you stand hard down on the brake pedal, (don't know why she is standing on the pedal this hard)
3 - the engine seems to stumble a bit, like there is a vacum interupption or something
4 - right after that stumble, the brake pedal goes soft and moves all the way to the floor
5 - once the pedal bottoms out, the car starts to move a bit, then the pedal hits the absolute bottom and it will hold the car, but your all the way at the bottom

Now, my thinking has always been, that if the master cylider goes bad and your pedal is allowed to bottom out like this that the brake fluid MUST be leaving the system somehow and the fluid should be low...right?

But on this car I'm not seeing any fluid leave the system so I'm concerned that the 650.00 master cylinder replacement will not correct this issue.

Any experience out there?

New member here for specifically this issue.

Background on car
1995 VDP white with tan leather int
65k miles
Rust around sunroof, needs the entire roof replaced from donor car
bought for 5k approx 10k miles ago, then immediately did the 6k worth of required neglected maint
Car purrs like a kitten, shifts perfectly and regardless of me wanting to sell it before it breaks us, the wife wants to keep it

I replaced all shock busings, (guy told me not to replace the shocks, all hoses, valve cover gasket, (I did it first, used sealant on the gasket, LEAKED REALLY BAD) took it to my guy and he fixed my mistake
Rear axle seals / bearings, etc...
and regular maint
4 new tires and new brakes all the way around with new rotors in front

Desp needs a fixed pwr steering system, currently leaks and causes my belts to squeek driving me nuts