2nd Gen Non-Engine/Transmission brake problems

[Rosshatfield]

My 95 2500 is having brake issues when backing up. The brake light and abs light will come on. The peddle gets hard and the brakes fail. Once I strart travelling forward the problem goes away. Any Ideas?

 

[bmoeller]

Do you have any vacuum leaks? Weird that it only seems to want to do it in reverse.