Converting Hydroboost Brake System To Vacuum Assist
Mark Stewart
Background
The 1984-1985 Grand Nationals and Turbo Regals came equipped with a power brake system known as "Hydroboost". This system used a hydraulic cylinder fed by the power steering pump to provide assist for the brakes. While the system was effective, it had drawbacks. The first, since it was hydraulic, it was inevitably prone to leaks. The surest sign that your Hydroboost system needed attention was a trickle of power steering fluid down the firewall (on the outside if you were lucky). Another drawback was that if the belt slipped, due to splashed water from a puddle, for instance, you not only lost power steering but most of you brakes as well. Not a pleasant experience in a rain storm. Another drawback was cost. A new Hydroboost cylinder from GM runs upwards of $800, and a rebuilt one is $125 or better as of this writing. So it was only a matter of time until someone found a way to replace the system with something better.
Something Better
The something better was just a matter of retrofitting the vacuum assist from a normally-aspirated '84-85 Regal, Cutlass, or Monte Carlo (G-body)
What You Will need
To complete the conversion, you'll need the following:
  • 1 foot of 3 inch exhaust tubing ($5 from a muffler shop)
  • 1 - 3 inch rubber elbow ($15 from a truck parts shop)
  • 1 - 3 inch rubber straight coupling ($10 from a truck parts shop)
  • 4 - 3 inch hose clamps
  • 1 - spring-fit oil breather cap (if you don't have a valve cover breather installed already)
  • 1 - Vacuum brake canister from a '84/'85 V6 G-body (Regal, Cutlass, etc.) ($90 new, less used)
  • 1 - Power steering pressure hose for a '84/'85 V6 G-body ($20 new)
  • 1 - '84/'85 G-body brake pedal ($15 from a junk yard)
  • 2 feet of 3/8 inch fuel/vacuum hose ($2)
Procedure
You will notice the 3 inch exhaust tubing and rubber hose included in the parts list. That's because to install the vacuum canister, you must first replace the stock MAF-to-Throttle Body pipe with a new inlet pipe that will clear the canister.
  1. Remove the stock inlet pipe. If you still have the stock oil filler tube on the driver's side valve cover, disconnect the breather hose that goes to the inlet pipe and cap the port on the oil filler tube. Remove the oil filler tube and reinstall it 180 degrees out of position so that the capped breather port now faces forward and the filler is aimed toward the master cylinder. Install the oil breather cap into the end of the breather tube. This will provide ventilation for your crankcase now that you won't be putting all that hot oily vapor back into your turbo.
  2. Take the 3 inch elbow and cut one end of the elbow back to the beginning of the elbow radius. This end clamps to the inlet of the throttle body. A slight angle-cut may be required to aim the other end of the elbow at the outlet of the MAF. Cut the 3 inch exhaust tubing to length so that approximately one inch fits inside the 3 inch elbow hose end. Cut the 3 inch straight hose to length and fit it to the outlet of the MAF and the inlet side of the 3 inch tubing, leaving enough overlap to secure it with the 3 inch clamps. Tighten up the clamps and the inlet pipe is done!
  3. To remove the Hydroboost cylinder, first crawl under the dash and disconnect and remove the brake pedal. You need to replace the Hydroboost pedal with the '84/'85 pedal because the actuator pins are different diameters. Inside the engine compartment, disconnect the three hydraulic hoses connected to the Hydroboost cylinder. One comes from the power steering pump, one feeds pressure to the power steering box from the Hydroboost, and one is the low pressure return to the pump. Cut the low pressure return hose from the Hydroboost where it returns to the power steering pump, leaving enough hose at the pump to install a suitable plug and clamp. Disconnect the high-pressure feed hose at the power steering pump (catch the fluid from the pump!) and set it aside. Also disconnect the high-pressure feed hose between the Hydroboost cylinder and the power steering box and set it aside. Crawl back under the dash and remove the four nuts securing the Hydroboost cylinder to the firewall. Pull the Hydroboost free from the firewall and set it in a dark corner where you can forget about it.
  4. Installation of the vacuum canister is straightforward. Insert the four studs on the back of the canister into the four holes in the firewall and install and tighten the four nuts from under the dash. Then install the brake pedal from the '84/'85 N/A car. Be patient, its tough to reach that far up under the dash and install the bolt/nut for the pedal.
  5. Back inside the engine compartment, cut a length of 3/8 inch PCV/fuel hose and route it from the vacuum canister checkvalve to the vacuum block on top of the throttle body. Clamp both ends of the hose.
  6. To complete the installation, install the power steering pressure hose from the N/A V6 car between the pressure fitting on the back of the pump and the pressure fitting on the power steering box. You may have to remove the pump to get at the pressure fitting on the back. The pressure hose may also need to be tweaked a little, but is easily accomplished with a hand tubing bender. Tighten everything up, fill the power steering pump reservoir, and go for a test drive. You will notice that the pedal effort is lighter with the vacuum system, but full braking power is still available.

That's it...........!


Last updated: