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Old 12-04-2010, 10:44 AM
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Late model variable assist PS adaptation (B-body fleetwood)

Long story short, I'm building a dual purpose street/road race car from a 67 LeMans. I have a couple spare 94-97 Fleetwood PS pumps with variable assist sitting around and wondered if I could use one... read on for more info.

I have been studying the wiring diagrams and searching. I know the basics. The computer uses input from the VSS and the steering wheel speed sensor to tell the PCM to vary the pressure using a pintle valve thereby varying assist to the box. The only thing I don't know is what kind of signal is sent to the actuator to make it work. PWM? Variable voltage?

I was thinking if its simple, I could use a potentiometer, multi position switch or DPDT to control the assist based on my driving.

The other hurdle I have is that the LeMans will have a R&P instead of a regular recirc ball box, and I know the pressure requirements for R&P are different (lower) so I may or may not be able to use the stock Fleetwood pump for this application. However, if I could use the valving plumbed in/adapted to another pump it may still fly

Your thoughts? Basically I'm looking for some general education on the setup so I can determine if its something I should pursue or skip.

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Old 12-04-2010, 11:44 AM
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If I'm not mistaken , R&P uses lower pressures, also the EVO systems where fairly problematic, I for one have had numerous instances of "twitchy" unwanted boost in pressure in the middle of a turn,high failure rates in the steering column sensor. It got so bad on the C/K pickups that GM offers a kit to retro fit the P/S pumps to a fixed orifice now and I don't believe they offer replacement EVO valves anymore, Just too many problems.
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Old 12-04-2010, 12:37 PM
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So, regardless of whether or not it would work, it might suck

Any other ideas for variable assist? Any other OEM manufacturers of variable assist that I might be able to scavenge/adapt? I know that early Acura Legends had a variable assist with a mechanical actuation off a driven speedo-type gear. The helical cut on the driven gear would push out on a valve as you went faster thereby reducing assist. The only problem I see with that is that the gear/valve assembly bolted into a proprietary housing on the transmission and would be nearly impossible to adapt.

I have heard of the pressure difference for R&P as well. I was told that regular boxes usually take 1800-3000 psi and R&Ps typicall operate more in the 800-1500 psi range.
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Old 12-06-2010, 11:23 AM
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Quote:
Originally Posted by curtis73
The only thing I don't know is what kind of signal is sent to the actuator to make it work. PWM?
Yes, so you need a pulse generator. I've been considering doing the same thing. You don't even need the pump, just the pressure control valve and solenoid that unbolts from the back of the pump. Most 90s GM trucks have this system also.
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Old 12-06-2010, 08:05 PM
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Joe, have you discovered any grassroots way of generating a PWM signal?

This all might be as simple as an adjustable industrial regulator and skip the electrical part. Maybe mount it with a bellcrank and a push/pull cable
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