Brakes on wifes 1990 2.5 300d
 

When my wife first cranks her car after sitting 3 or 4 hours she has good pedal on her brakes. Then the pedal goes hard for a minute or two then the pedal goes back to good brake. If only sitting for a short period of time she has good soft pedal. I have not checked for vaccuum leaks with any type of gauge. Any ideas out there.

The brake booster is operated directly from the vacuum pump..that pump would be my starting point.