HWH Jacks Not Lifting the Bus...84 FC

[dthollis1961]

My jacks have worked fine for several months till today. Now they
swing down and start to lift, but they don't lift very far. All 4
jacks have the same symptoms. Tank is full, motor runs and there are
no leaks. When the jacks reach the point that they stop raising the
bus, the motor/pump sound changes pitch as though a relief valve is
opening. Anyone here have the same sympoms that can comment?

Thanks,
David Hollis 84 FC35 Springfield,IL