Heidts valve (power steering) adjustment

[mcwho]

For those that have this valve this question is for you.

I am using a standard GM type power steering pump and a mustang power rack.

I have mine so that there is 4 full turns from where the adjustment knob has no more threads and comes off the body. Not sure how few threads is safe to have with the pressure in there. If I turn it all the way in I count about 8 turns of adjustment. As I remember from the instructions turning it counter clockwise was supposed to make the power steering effect less.

I don't know if it is safe tur turn it our more turns or not. But it is still kinda sensitive.

[GoDadGo]

I'm not familiar with that valve, but this is what we used when we stuffed a Small Block Chevy, which uses a GM Saginaw Pump, in a Fox Body Mustang.

http://www.jegs.com/i/JEGS-Performan...60791/10002/-1

No adjustment was possible since it just restricted the flow, but it worked fine and didn't over boost or under boost the system.

[Jeff Kleiner]

Hey Bob,
Got your PM asking for input but my info may be of limited use since I've never tried to mix a GM pump with Ford rack (owing to my "don't try to reinvent the wheel unnecessarily" philosophy all of mine have been Ford/Ford). With the all Ford combination 3 to 3 1/2 turns out is where I like to run for street use (I go to full assist on track and for auto-x). Much past about 4 turns out you'll begin to lose the assist altogether and the steering will become jerky as so much of the pressure is being bypassed. I do not know how the GM pump pressure compares or if it may be over assisting the Mustang rack. Perhaps if there is indeed a significant difference in the normal operating pressure ranges between the GM pump and Ford rack it may explain why you are not feeling a noticeable change. That's my best guess anyway...

Jeff

[2bking]

I have the same combo, GM pump and Mustang rack. I found when I tried to dial down the pressure, the pump couldn't keep up with the rack on a fast turn such as a U turn on the street. I now have it set for full pressure and like it. I could have saved a lot of money by not installing the Heidts valve.

[mcwho]

Thanks for the input, my engine builder insisted on putting the GM pump in and they seem to be prevalent in the industry for whatever reason. I have mine dialed out to where there is only about 4 turns of thread, left. Any more than that I feel would be dangerous.

As far as that valve that Godadgo mentioned, I have never seen that before but have read many times about cutting the spring that inside the GM style pump.

This build has certainly been a learning experience for me, my byword is this:

Know your limitations !

[mcwho]

King,

Wish I had known about this part as well, I spent a lot of time and money having the four hoses for the PS made up.

[GoDadGo]

Bob,

We came across that valve when we realized that the Saginaw Pump pushed too much fluid for the Mustang Rack so it was way over boosted and had no road feel.
That part was cheap and did the trick; however, I cannot understand why your engine guy wanted to use that pump on a Ford Engine.
I get it when you do something stupid and go off the reservation with an alternate power plant, but don't understand the reasoning for his recommendation.
Just remember that like you, I'm too am a first time builder and part time wrench swinger.
Good Luck!

Steve

[Jeff Kleiner]

...
I get it when you do something stupid and go off the reservation with an alternate power plant, but don't understand the reasoning for his recommendation....

Like I told ya' the other day---Heyoka

OK, so after the input from King and Steve it sounds as if my speculation that the GM pump and Ford rack really don't like to play well together may have some validity but also that they can be forced to do so, at least to some extent, by changing to the flow control valve that Steve referenced. Whether this will allow the Heidt's valve to function as intended remains unknown.

Jeff

[johnnybgoode]

If you are running the GM Type II pump you need to put one of these Borgeson kits (PN 899001) in it to lower the pressure for the Mustang rack (from 1000-1200 PSI to 700-800). The kit includes simple instructions, shims, and all the parts you'll need to do the job including a tool to hold unit in a vice while installing the shims. I used 3 shims and the steering feels just about right. The Heidts valve will then let you fine tune from there. Scott

Canon 006 (2).JPGCanon 013 (2).JPG

[2bking]

I should explain the problem a little better that I experienced. I have the Heidt's valve located close to the PS pump and about 24 inches of braided hose to the rack and 24 inches back to the valve. There is a relationship between volume and pressure for the fluid traveling through the hoses so at low engine RPMs and a constant low pressure dialed in the valve, the flow can't keep up with the fast displacement in the rack such as required in a slow moving U turn. With the valve turned up to raise the pressure, the flow in the hose is increased. Two things would help or fix the problem. Either increase the diameter of the high and low pressure hoses between the rack and valve or move the Heidt's valve close to the rack to reduce the line loss. I didn't notice much difference in the steering effort between the lower pressure setting and higher one so I suspect my setup isn't ideal for the Heidt's valve application.

[mosh1999]

As you know, the over sensitivity is due to the pressure being too high in the PS system in relation to the weight of the vehicle (normal driving conditions).

2bking is correct in his statement that there is relationship between pressure and volume. Whether you are running a Saginaw or the Type II TC pump, make sure the return line is larger than the pressure line. What size lines are you running?

The Mustang II racks were used in cars almost 1,000lbs more than the FF Cobra. 700-800 psi should be about right, but I have had customers call me on lighter custom 32 Ford builds that get into the 600 psi range. I wouldn't recommend that low, but I have had people tell me that is what works for them. Do you know the pressure you are running right now?

Todd
Unisteer
Sales and Tech

[2bking]

What size lines are you running? Do you know the pressure you are running right now?

Todd
Unisteer
Sales and Tech

I am using -6 AN hoses because that is what the fittings at the Heidt's valve and rack are sized for without adding adapters to increase the hose size. For my setup there is additional length of the -6 AN hose from the Heidt's valve to the cooler then to the reservoir. I'm now using full pressure from the GM type 2 pump which is said to be too high for the Mustang rack but I don't think that is a problem until the rack reaches full travel or hits a stop in the steering system.

[totem]

The pressure vs flow relation to level of assist is difficult to understand.

Looking at the Heidts valve patent, I understand it is a return type pressure limiting valve that is independant of flow. However, reducing pressure will reduce flow.

KRC pumps have swapable valve fitting with different flows.

Both are intended to adjust the level of assist but one works on pressure, the other on flow!

I might be wrong but I think that when there is no steering effort, oil flows in the system at zero pressure, keeping the pump cool. when effort is required pressure is build up to provide assist.

From that logic, I think lower pressure will lower the maximum level of assist but low flow will reduce the rate of assist.

But since there is still a pressure/flow relation, I cannot say which is best to improve steering feeling.

[totem]

Here are two references:
Heidt patent: https://patents.google.com/patent/US6029766A/en
KRC tech docs:
. http://www.krcpower.com/files/flow_valve2013Tech.pdf
. http://www.krcpower.com/files/flow_valve2013chart.pdf

[2bking]

The pressure vs flow relation to level of assist is difficult to understand.

Looking at the Heidts valve patent, I understand it is a return type pressure limiting valve that is independant of flow. However, reducing pressure will reduce flow.

KRC pumps have swapable valve fitting with different flows.

Both are intended to adjust the level of assist but one works on pressure, the other on flow!

I might be wrong but I think that when there is no steering effort, oil flows in the system at zero pressure, keeping the pump cool. when effort is required pressure is build up to provide assist.

From that logic, I think lower pressure will lower the maximum level of assist but low flow will reduce the rate of assist.

But since there is still a pressure/flow relation, I cannot say which is best to improve steering feeling.

You are correct in the way you understand the principle of operation. It's the lines between the pump and reservoir that have the flow vs. pressure relation where it takes a certain pressure to deliver a certain flow so lowering the pressure certainly lowers the assist but also the volume of fluid available. The pump being a constant volume per revolution hydraulic device will put out that volume at any pressure until something breaks. Any pressure reducing device whether inside the pump or external has to reduce the volume to lower the pressure.

The problem occurs at high volume and pressure demands of the rack such as making a U turn and this is the only place I incurred the problem. I would get about a half a turn of the steering wheel with power assist and then it was suddenly all manual input needed to complete the turn. I first thought it was due to the belt slipping on the pump pulley and tighten the belt several times. Only when I dialed in more pressure to the rack did the problem go away. It could possible be a rack issue and not the pressure volume relationship.