79 C70 with hard brakes - bad hydro-vac?

[hkopp]

I've been a member for a while, but usually hang out in the 60-66 k10 area. I have a 79 C70 with hydro-vac that I recently acquired. Its brakes are nearly non existent and hard, and require pumping of the peddle then pressing VERY hard to make the truck stop. I'm assuming its a bad hydro-vac unit under the side step, has anyone experienced this before? I see reman units for around $160 with a core, but would rather hear some feedback before I start throwing parts at it. I've had a C70 in the past and when working correctly the hydro-vac brakes nearly throw you thru the windshield, even with a full load.

Any troubleshooting procedures or pages dedicated to this, or is this a common symptom of a bad h-vac? Thanks!