Because it has a hydraulic booster that supplies both systems and something is wrong with it.
Its has HydraBoost Braked, operates off the power steering pump.
The Astro Van power steering and brakes work off the same pupm. Check the pump for fluid. If it's full and the brakes and steering still hard you must replace the pump
You can add power steering fluid to your 1988 Chevy Astro by removing the top to the power steering fluid reservoir. Pour the fluid directly into the reservoir.
check the power steering fluid, also check to see if the belt is on
under the hood
For a 1987 there is no automatic doors or windows for A Chevy Astro Fuse is underneath the steering colum along the Driver side feet...
$60-$80
Two things: 1. Your power steering pump is quite - this will affect your steering (of course) but will effect the brakes too 2. You lost your main belt that operates all the aulterator, steering, cooling system and brakes (the serpantine belt) - if the belt is still on and tight - its number one (I had both happen1)
The power steering pump also provides power for the power brakes.
the problem is that your saft on your power stearing pump broke and that afects your power brakes to
i think that engine is a 4.3 ltr, there for the power steering unit is forward face aft lower right hand side of the engine.
The power steering and the power brakes share the same pump. The pump belt may be loose, the system may be low on fluid in which case you have a leak somewhere or the pump may be faulty.