How-To: DIY Hydroboost on GM Vehicles

Hydroboost is a power assist for the braking system that runs off the power steering pump hydraulics. This have several advantages: higher line pressure over a manual setup or vacuum booster, and if running a larger cam which produces less overall vacuum, it simply is a better option to get awesome braking back.

Another problem is that complete kits from companies range from from $900-1200! A new GM hydroboost unit runs $200-300, so where is all the extra cost coming from? Turns out the bracket to mount hydroboost to firewall and pushrod are really the only custom “items” needed to successfully install one in your vehicle. So lets cover what is needed for the swap.

Install Video

The video at the top of this page goes over the mock-up and install of hydroboost and T56 master cylinder install. I would watch the entire video and then reference the below on what parts where used.

Hydroboost Unit

The hydroboost unit you want to use is AC DELCO 178-1036, which is for a 2011 Silverado 2500. This is a brand new unit, and comes fully “stuffed” with the small pushrod and “star” centering plate. Reman units will not come with these parts and they alone will cost $60 on ebay. This hydrobooster is called the “late short MC pushrod” style. Basically the mating master cylinder needs to have a divot for the pushod. More on that later.

The first thing you need to do is remove the bracket that comes with the unit. I used a cutoff wheel to remove one of the studs on the mounting plate. Then use a 1-7/8″ crowfoot to remove the nut. This crowfoot costs around $16 and is much cheaper that the $80-100 special sockets required to install those fancy billet mounting brackets.

Next up is to modify the pushrod. Most older GM vehicles require that the pushrod be threaded 3/8″-24. The unit comes with a rod end type connection. You can cut this off and thread it with a die, although I have not done this and people say it is rather difficult. The OD is super close for thread size needed. I opted to cut up a universal booster extension rod w/clevis and weld it on. Refer to the install video on how I set this up.

Mounting Bracket

Now you need a mounting bracket. I designed 2 styles of brackets that should work for many GM applications. This design is “universal”, which allows you to mount the booster in any orientation. You can flip it so the accumulator (silver canister) to mount towards the driver or passenger side. Both designs only require the $16 crowfoot to install. No expensive special sockets are needed.

HTMR Hydroboost Only Bracket

This bracket mounts the hydroboost at a 6° angle for more valve cover clearance. I have created a template to check vehicle fitment. Print and cut out the template. Place on firewall and if holes line up and it sits flat with the rectangle, then the bracket will work

I used the OEM type seal used in vacuum boosters to seal the hydrobooster to the firewall. Trimming is required and it ends up fitting OK.

HTMR Hydroboost T56 Combo Bracket

This bracket mounts hydroboost and a clutch master cylinder for the 68-72′ GM A Body vehicles.

The following parts were used and/or modified to make everything work.

• Tick F Body master cylinder 7/8″ bore (stock is 3/4″). Mount with button head instead of hex head fasteners.
• Stock A Body clutch pedal ratio is 5:1. Modify ratio to 6:1 by moving pivot point up 0.4″.
• 04-06 LS1 LS2 GTO T56 Clutch Fluid Reservoir
• Hose by the foot for reservoir

Power Steering Lines & Adapters

I used the CPP Hose Kit HAHK-R. These lines are super easy to cut to length and assemble. The kit comes with “flare” style adapters, so be aware of that. My Chevelle has a Grand Cherokee PS box swap which uses the later O-ring style type connection. You can buy the O-ring to AN adapters from Holley.

EARL’S -6 AN MALE TO 16MM X 1.50 MALE

EARL’S -6 AN MALE TO 18MM X 1.50 MALE

I will say that some of these CPP fittings were hard to seal up. I went as far as using valve lapping compound and “grinding” the flare a bit to the adapter, which helped. Then I found that these cool little copper AN seals.

My power steering pump came out of a GM truck that originally had hydroboost, and the reservoir had 2 return fittings. The one above the fluid level is the hydroboost return. If you only have one return port, then you have to install a “tee” fitting. The power steering gearbox return flows straight through the tee, while the hydroboost return needs to be hooked up to the 90° fitting on the tee.

As far as routing, the high pressure line exits the PS pump and goes to the hydroboost, then the power steering box.

Master Cylinder Selection

With hydroboost, you will need the proper master cylinder bore size. For most applications, a 1-1/8″ bore size will work well. If your brakes are too sensitive, then a LARGER bore size will INCREASE pedal effort.

AC DELCO 18M91 – 77 corvette 1-1/8″ bore short pushrod, cast iron