The best replacement for hydroboost is vacuum.

The best alternatives to hydroboost are rated as following:
★★★★★  vacuum
★★★  vacuum boost
★  vacuum booster
  brake booster

Your alternative for hydroboost is not listed? Suggest!
Speaking about hydroboost, one probably shouldn't forget about manual steering.

Other search terms related to hydroboost and their ratings are:
★★★★★ manual steering
★★★ full hydro steering
★★★ power steering
★ master cylinder
You have in mind a companion for hydroboost and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of hydroboost in all years. Click on graph for more.
hydroboost
vacuum
vacuum boost