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Electric power steering pumps and hydroboost, will it work?

5743 Views 56 Replies 8 Participants Last post by  SafariMike
Making this thread to either be a monument to my failure or a how-to on my success

Hydroboost is a system which uses hydraulic pressure from the power steering system, as the pressure to press the brake master cylinder, instead of vacuum or electrics

I'm doing this instead of electric power steering + electric brake booster because this will give significantly better breaking and steering feedback and feel, also this has much higher packaging efficiency, and comes with a lot less fabrication requirements for bolting stuff to the firewall. It's also way cheaper and uses stuff the car came with.

The pump is a volvo electric power steering pump, from an 04-13 volvo,
04-13 Volvo Electric Power Steering Pump S40 V50 OEM Bracket/Pigtails Included | eBay
it uses up to 80 amps at peak when the steering is at lock, has a beefy main power input plug and a little canbus input plug as well.

it'll be paired with a hydratech brake booster and a flaming river steering rack
Hydratech Braking Systems :: 1968-1982 C3 Corvette Hydraulic Brake Assist System Listings
1967-82 Corvette Power Rack & Pinion Cradle Kit - No Column
in a 1971 corvette

big unknowns as of now:
  • unclear if backpressure is a problem, most hydroboost systems have two separate return lines because the brake booster HATES backpressure. the volvo pump has only a single return inlet...
  • unclear if the "failsafe mode" of the pump, which runs it at 50% speed, is sufficient to drive the system, getting good steering assist and good brake pressure, but not overboosted steering
  • unclear if adding variable speed to the pump, using a control board like this: Universal PSC/NMS-PSC – NMStec , will cause the braking force to be significantly reduced at low pump RPM. the idea being that outside of a parking lot, you don't need that much steering assist so why not turn it down pretty low
  • unclear what is a good way to silence the pump, since its pretty loud and annoying at low speeds, i'll need to put it into some kind of sound-resistant box, and still keep it somewhat cool in there (possibly running the PS hose around the motor a few times, and putting the fluid through a little heat exchanger somewhere)

I'm about to purchase the pump, here goes nothing

some videos on the pump from gas car builds

here's how it sounds when running, very forklift esque
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I doubt the pump can react fast enough to brake pedal force input.

It's designed to work with a PS pump, so no need to go beyond what a belt-driven (or hydroboost) pump does.
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I seem to recall some trucks having a dedicated hydroboost electric pump....

Too busy to do an extensive search: BENDIX BOSCH HYDROMAX ELECTRIC PUMP MOTOR 2771544
Which is why you PWM the Volvo pump speed...

Good writeup - thnks for sharing. May be useful to someone some day.
You can always run a dedicated EPS pump for each system, i.e. two Volvos or whatever ones you pick.
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That may be related to the capacity of the relief dump/valve/regulator or return line.
You can always measure the flow and pressure...since you have the pump and sounds like you need to dial it in, anyway.
A bucket for flow

A guage for pressure.

Farm tractor supply/dealer is a good place for hydraulic stuff.
Why are you using a Foxbody rack on a Corvette, anyway?
So you would pwm the non-trigger 12v I.e., the 80amp 12v source? With a ss relay?
Not sure, never looked into the details. @Nmstec's board takes care of the pump speed, other pumps have PWM signal leads iirc. I still have his board sitting in a box with bigger fish to fry tight now.
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Funny how we used to put headers and glass packs on, and flip/remove air cleaner housings, to make a car LOUDER 😂
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The only converter I know of that's contemplated Hydroboost is @joekitch
Full lock dumps flow through the relief valve, dropping the hydraulic pressure to near zero.

What you might try is a 150psi or so relief valve in the return line from the steering rack/box to the reservoir and the brake pressure return line going directly to the reservoir. That means the Hydroboost never sees less than 150psi, even at full lock and the power steering runs at 150psi lower (or higher? my brain's fried right now) pressure.
You know, being electric, vs having to figure out belt drives, you can run two electric pumps on two circuits, with the brake pump pressurizing an accumulator so it's not running all the time....possibly using a much smaller pump given the limited fluid volume being used.
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