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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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If you use my controller (above you linked to), I can add brake switch provision to increase assist. You can as well just install a pressure sensor and my controller can compensate for it. A similar style system is used using a volvo pump on a schooner (some fancy boat). They attached pressure sensor to my controller that whenever low pressure side sees a difference in pressures, pump increases to assist to the high pressure side.
Personally I don't think this is the right way to do this, and would instead recommend an iBooster as a seperate system, or perhaps dual hydro pumps (even then double the noise).
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
I will have to call this out as wrong. Any Ford variant pump (Mazda and volvo) has a 1200psi internal bypass to my knowledge.

On the other hand, the pump itself isn't the part that creates the pressure, only the flow.
The pump obviously is the part which creates the pressure - that's what pumps do. The pump does not control the pressure - it is controlled on a flow basis, and the pressure that it must produce to push that flow is determined by the valve in the powered device (steering rack or brake booster).

Higher-than-required pressure capability of the pump isn't a problem by itself. That high pressure will only occur if the steering rack or brake booster excessively restricts flow.
Semantics, but yes, restriction is what dictates pressure was my point.
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Some info I DO have on the volvo/mazda pumps:

0-6375 RPM
Module temp limit is 110*C
Motor temp limit is 175*C
1200 PSI internal bypass

TRW type 1 Astra pumps do have around 1700psi limit, but they are not controllable. instead they use a valve on the high pressure side to raise and lower pressure.
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

Good news. I now support Dodge/Chrysler 12-20 EHPAS pumps. They are 1700psi @2.5 GPM.
Some more info on them: Support for a new, and most powerful EHPAS we’ve seen yet – NMStec
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Volvo/Mazda pumps are 1200psi & 1.91 gpm.
Charger/jeep pumps are 1700psi & 2.5 gpm.
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