Rack and pinion steering

[cajos1968]

Sky,

Can't you use a bigger pulley on the p/s pump, to reduce the number of rotations of the p/s pump, thus reducing pressure?

 

[Sky65]

Sky,

Can't you use a bigger pulley on the p/s pump, to reduce the number of rotations of the p/s pump, thus reducing pressure?

I thought about trying that but I never followed up. I'm not sure how much pulley selection there is. I also think at driving speeds even a larger pulley will still spin the pump up to max pressure. The larger pulley may only affect low rpms which is where you generally want more assist. Good thought though. :beer:

 

[cajos1968]

It took me some minutes but I remember the solution!! Only 85 usd.

Adjustable Power steering valve, by Heidts

http://www.heidts.com/index.cfm/page/ptype=product/product_id=210/category_id=88/home_id=88/mode=prod/prd210.htm

Let me know how it works out.

 

[BBShark]

The maximum pressure for a PS pump is achieved at lower than idle speeds. There is a pressure relief valve in the pump that internally bypasses the fluid. So putting a bigger pulley on will not reduce pressure.

The bypass pressure in a C2-3 is supposed to be 950psi. I suspect that somewhere over the lifetime of the car, most pumps have been replaced with rebuilt passenger car pumps that are 1250psi or higher.

 

[cajos1968]

BB any opinion on the Adjustable Power Steering Valve? Could that be answer?

 

[turtlevette]

The bypass pressure in a C2-3 is supposed to be 950psi. I suspect that somewhere over the lifetime of the car, most pumps have been replaced with rebuilt passenger car pumps that are 1250psi or higher.

I'm wondering if that difference is because of a design difference like different vanes or just a different bypass spring.

The problem with reducing pressure using bypass is that you do it at the expense of volume capacity. So you get just the opposite effect that you want. You want more assist at idle and less as crusing speed. At cruise the lower pressure will provide a firmer feel but as soon as you need to make a quick turn of the wheel, the pumps volume capacity will not be able to keep up because a large part of its volume capacity is used up already via the bypass.

Am i full of crap? I need to get out my service manual and read up on theory of operation.

 

[BBShark]

BB any opinion on the Adjustable Power Steering Valve? Could that be answer?

The problem with the Heidts valve is that it is a fixed restriction. Pressure is reduced and flow is reduced. This would be a problem if you were, for example, turning the wheel quickly to avoid a collision:shocking:. This is called pump catch up where the flow demand is higer than the capability.

The valve in the Saginaw pump is easily removed and bypass pressure changed with shims.

 

[Sky65]

BB any opinion on the Adjustable Power Steering Valve? Could that be answer?

The valve in the Saginaw pump is easily removed and bypass pressure changed with shims.

I did that mod. I bought a "shim kit" and installed all the supplied shims. I think it did help but I would like to drop the assist a little more. I read somewhere the Saginaw pumps were used with different pressure/volume flow control valves on differant cars. Anyone know if the valves are sold separately from the pump? I would like to try a lower volume valve.

 

[BBShark]

Any valves that restrict flow while reducing pressure won't work very well.

You may be talking about the EVO valve used by GM, Ford and Jeep. That is used to control pressure based on road speed and steering input. I am working on a PWM control for this but so far I have only had it working on a bench.

The picture below shows an EVO contol valve (lower right).

 

[69427]

Any valves that restrict flow while reducing pressure won't work very well.

You may be talking about the EVO valve used by GM, Ford and Jeep. That is used to control pressure based on road speed and steering input. I am working on a PWM control for this but so far I have only had it working on a bench.

The picture below shows an EVO contol valve (lower right).

Keep me updated on that project. While I've been working on my C4 suspension transplant, I've been trying to figure out a use for the ABS wheel speed sensor lines. Perhaps an interface box to read the wheel signal, and then modulate the PW of the solenoid driver for the pump solenoid as the speed changes. I did a lot of work on solenoid drivers and controllers for PCMs and electronic transmissions before I retired. This ought to be a similar concept. Could be interesting.

 

[cajos1968]

I found this article on the pressure relief valve..

http://www.heidts.com/pdf/art1.pdf