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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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Dynamically speeding the pump up with brake force is an interesting idea, although that may feel extremely weird if I'm decelerating while turning, with the wheel getting lighter as I brake harder into the turn
the hydroboost system in my car has a basic belt fed power steering pump, the only distinction begin two separate return lines, i dont think a two loop system is necessary, more like just characterizing what happens to my brake feel at lower flow rates. from elsewhere it sounds like lower flow will mean less assist on brakes so my brakes become "more manual" in a sense, which might not be that big of a deal? unsure.

i'm trying to call up the tech support line for a company called Tuff Stuff performance which deals a lot in hydroboost in passenger cars
called up hydratech this morning and got a tech on the line, i took some notes:

  • they haven't heard of anyone successfully using an electric pump with their system, they always say it just "didnt work"
  • ideal flow range is 2.2 to 2.6 gpm
  • over 2.6 causes churn and aerates the system, cause erraticness, pump noise
    • however this is specific to the pump, if the pump doesn't aerate at higher flow rates, it doesn't matter
  • can go down to 2gph since the foxbody rack needs that
  • pressure doesn't control control quickness on steering, flow flow rate does
  • pump reservoir should be vented, otherwise it can build up pressure, which heats the fluid
  • avoid overheating the fluid since it causes the fluid to expand and lose braking pressure
  • recommend synthetic fluid
  • 2psi of backpressure will self-apply the brakes, if there's a T-line on the return it must be within 3" of the brakes
  • using a PS cooler is a bad idea without two return lines, coolers can cause some backpressure which is BAD
  • to add another return line to the reservoir, use bulkhead adapters, and then attach using socketless AN-6 fitting
  • needs to return to the primary resevoir, not T off the secondary reservoir
according to this random thread Volvo EPAS Conversion , this volvo pump can do up to 1700psi at 4.4gpm flow rate, which is way beyond what they're used to apparently, and at this point im a little concerned this thing could blow the steering rack apart?

time to call flaming river and ask how much psi their rack can take
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Considering I plan to hook the pump up to my current rack and hydraboost soon, hopefully it'll be useful to me someday

The back pressure and heat situation has me a little worried though. Tapping a new return line is probably for the best but that may be really hard because it's a rounded reservoir....I feel like putting a T on the little vertical tube to the above secondary reservoir is the play since the brake booster return only squirts out a tablespoon whenever you lift off the brakes apparently
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I forgot to mention my pump arrived, paid about $160 on eBay for it, and it came with the data end power harnesses plus the big mounting cage, which is nice.

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It's not entirely clear to me what they mean by "quickness" here.
From the way the guy said it, too high gpm results in the rack being over boosted and very little steering input resulting in a lot of steering "sneeze and you fly off the highway", etc. This is from experimenting with foxbody racks
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The hydratech guy very strongly recommend that the reservoir have a pressure release valve for exactly that reason

Just got off the phone with the guys who make my steering rack (flaming river) and they said their rack operates between 700 and 1100 psi ideally, and their pumps deliver 2.5gpm flow rate so that's probably a good middle ground to shoot for.

He recommended adding a pressure reducer on the rack side of the hydroboost, since according to him hydroboost usually requires higher psi than their racks can take

Really wish I could get solid numbers on the psi/gpm the Volvo pump is rated at

The pressure reducer being on the rack side makes sense when looking at this diagram
Power Steering Gear Plumbing Diagram With & Without Hydro Boost
Font Line Parallel Engineering Circle


This also shows two separate returns to the reservoir so I think that's what I'll do, probably plumb the hydroboost return to the upper remote reservoir to boot so there's ZERO chance of back pressure
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I'm not actually sure how to measure that, sounds like it requires super specialized expensive equipment that hopefully some hot rod shops have that I can bring the pump to
Yeah but how to measure pressure without blowing things apart or burning the pump out

If I make a hardline loop with a gauge on it, wont that pressure burn the pump out almost immediately?

If I run it through my rack, it runs the risk of blowing seals from overpressure

And for flow, are you talking about literally just emptying one bucket of ps fluid into another with a stop watch? Won't the outflow be at insane pressure and kinda dangerous?

I was thinking of getting something like this to regulate psi from jump, some folks have used these for famously low PSI tolerant foxbody racks, but it isn't entirely clear if this is a flow restrictor or pressure restrictor

Why are you using a Foxbody rack on a Corvette, anyway?
Im not sure if the flaming river steering racks are the same design as the foxbody, but the foxbody racks are known for needing very little pressure/flow rate to operate, and anything beyond that makes them heavily overboosted

Pwm on the pump from jump is an interesting idea though, I believe they have a native pwm signal? Or maybe that was a different pump

With a pwm I could install the pump inline, start it at VERY slow speed with a pressure gauge in there somewhere
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Part of this plan is building a heavily sound reducing enclosure around the pump to cut the sound down by like 20 decibels

Hence why I'm looking at an intercooler for the pump
Well, engines sound cool
Electric hydraulic pumps sound like a forklift (not cool)
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A 1200psi bypass is encouraging, meaning I can probably use it with my current rack as a drop in and not blow it up immediately (probably), I'd still like to throw a flow rate meter and pressure meter on their for validation though

So next up is examination of the current plumbing, finding a good spot for the enclosed pump, and looking for replacement high pressure lines compatible with the existing fitting

Also need to find the model name of my current pump to see what it's rated psi/GPH is so I can match that later

Edit; actually, while a pressure gauge is easy and cheap, measuring flow is more expensive it seems. I'm lieu of that I can get one of many many used power steering analyzer kits for ~$100

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Picked up one of these, hopefully it'll work, not sure if I can use it alone with the pump though
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Probably a dumb question but the power connection is sized and fused for 80 amps max load right? Is your 12v battery struggling to push that much power? Have you got a meter on there to measure how many amps it's demanding?
Oh I thought you had a direct line. Yeah with amps like that you generally want it coming right off the battery

What's the plumbing diagram look like? In terms of which lines go where

Also, when test driving, pay very close attention to if the brakes try to self-apply, which would indicate back pressure issues, but the two separate return lines should fix that

Also also, consider surrounding the pump with some sound deadening, don't worry about heat since the thing needs to get to like 240F to actually start hitting thermal cut off limits and there's no way you'll hit that in a EV engine bay

Also x3, how did you plumb the other return line anyway? Just drill in the top and screw in a metal bung?
If you get brake issues, try swapping which return line goes where, since the return line on the bottom will see some back pressure from gravity, in that the neutral pressure of the fluid sitting in the reservoir will apply some default back pressure, but the top return line has none. The return feed from the brake system will be basically a trickle but back pressure on the brake side is bad

Hopefully you don't need to do something like having the pump physically below the level of the hydroboost
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