Hydroboost issues

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A few suggestions-

If you used a junkyard Hydroboost, get all the seals, spool valve and check valves working correctly with an overhaul kit from Pirate Jacks. This solved a few issues I had with a junkyard Astrovan Hydroboost.

The clearance of the actuator pin of the Hydroboost to the master cylinder cup that receives the pin is critical. .020" IIRC. You can buy a tool from Lisle to do the measurement or just use a dial caliper and a straigt-edge. They sell throw-away 3D-printed ones on ebay too

A power brake system with a hydroboost can be difficult to bleed. I've had some luck with a Mighty-vac pump to put some vacuum in the system. I put it under vacuum with the front wheels jacked up and turn the wheels lock to lock a few times, Repeat with engine running.


I've run a dedicated return to the reservoir and a "t" in the rack return line and haven't noted any difference, but some folks say they have. My latest pump is a Saginaw 'ham can' and I welded a -6AN fitting about an inch below the fluid level



When working correctly the hydroboost on my truck is fantastic, Hope this helps you some