Restricting Power Steering?

[Carpy2]

Hey everyone,

What's the best way to restrict the power steering unit to make steering input heavier? Finally trashed my leaky OEM rack and replaced the rack with a refurbed Z3 rack. Steering with a non-leaky rack feels way too light (compared to what I've been driving with for years). Some cars got a PS restrictor in the return line, mine did not. How much does this restrictor, well... restrict? Is this something I can make myself and experiment with -- eg. Cut the return line hose, and splice random diameter fittings inline and see what feels best? I don't know much about the system so this could be a super bad idea

Are there other methods to restricting PS without fully removing it? Do underdrive pulleys underdrive enough to notice?

Thanks

Notes: only steering rack and hoses were replaced, alignment is the same as before I replaced the rack, so I don't think alignment has anything to do with the change in steering stiffness. -3.5f/-2r of camber, +0.1f/0r total toe.

[pbonsalb]

I have an underdrive PS pulley and Z3 1.9 rack and 255/40 front tires and a restrictor in my reservoir return and my steering feel is still lighter than I would like. If you find something that makes it heavier, let us know. I think the Z3 1.9 is linear so maybe a progressive ZHP/Yellow Tag rack wound have a heavier on center feel. I don’t know.

[Carpy2]

Good to know, thanks for sharing.

I think I'm going to try and just put a hose clamp on the return line, and tighten it down to crimp the hose a bit. I will see if that makes any difference at all. But I'm still looking for some more suggestions. If crimping it doesn't work, I think I might try an inline reducer in the middle of the return line, just a more restricting restrictor I suppose.

I'll report back with my findings, thanks.

[pbonsalb]

The stock restrictor is pretty restrictive.

[Carpy2]

The stock restrictor is pretty restrictive.

Oh ok, I'll start with that then. I have a feeling I may want it heavier still though, so may still experiment a bit.

[pbonsalb]

I’d like it heavier. Post what you find. The restrictor is in the return line from the reservoir. I may have read somewhere that it is like a stopper that reduces the amount of foamy fluid returning — the solid fluid goes through the small hole. But I am not sure about that explanation.

[jayjaya29]

I have an underdrive PS pulley and Z3 1.9 rack and 255/40 front tires and a restrictor in my reservoir return and my steering feel is still lighter than I would like. If you find something that makes it heavier, let us know. I think the Z3 1.9 is linear so maybe a progressive ZHP/Yellow Tag rack wound have a heavier on center feel. I don’t know.

ZHP/330ci rack is linear, not progressive.

[pbonsalb]

Ok. So it would have no heavier on center feel than a Z3 1.9 rack?

[bluptgm3]

The factory (and quality aftermarket) return line should have the restricter.


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[blckstrm]

The factory (and quality aftermarket) return line should have the restricter.


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I had mine rebuilt by a local hydralic shop and they pulled the restrictor and stuck it in the new hose with a hose clamp to hold it in place.

I have a ZHP rack and I like it, but I'd love to get everyone together to feel how the other racks feel. I swapped to an E34 U-joint when I did my rack (and my original guibo was as soft as neoprene - it was trashed) and so never really had a good before/after.

[Carpy2]

Yeah I just realized I was looking at the wrong hose. It does have the restrictor in the return hose, which means steering still feels too light for my taste even with the restrictor in. I tried messing around with hose clamps, but wasn't able to collapse the hose enough to make a noticeable difference before backing off at the point I thought I may damage the hose.

I found this thread talking about making their own restrictor since their hose didn't have one. They mention the restrictor diameter being ~3mm. That's way smaller than I was picturing, but I think I'm going to experiment making (somehow, idk) a restrictor. Maybe, just a tad over 2mm, and go from there.

I'll do some googling to see if a regular hose fitting like this exists. I was just picturing a double barbed fitting that goes down to the above diameter in the middle. I wonder if an adjustable valve is possible? Then you could potentially tune your power steering to your liking, and change it whenever -- but I don't know what kind of pressure small valves like that can take. Actually I don't know how much pressure a regular hose clamped double barbed fitting can handle in the line either...

edit: converting to AN lines for just the return line and running something like this may be an option. Or maybe mess around with an inline hydraulic line flow restrictor like this. Put inline after the restrictor.

[bluptgm3]

I would measure the ID of the hose and drill the center of a piece of aluminum rod to your desired diameter - keep it simple. Clamp in place like the factory restricter.


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[pbonsalb]

But does the return line restrictor have anything to do with the heaviness or lightness of the PS, or is it just there to reduce foam in the rack during extreme driving? Some have run no restrictor unknowingly (they replace a leaking return hose with their own hose and did not even realize there was a restrictor in the old hose) and not noticed any difference.

[jayjaya29]

But does the return line restrictor have anything to do with the heaviness or lightness of the PS, or is it just there to reduce foam in the rack during extreme driving? Some have run no restrictor unknowingly (they replace a leaking return hose with their own hose and did not even realize there was a restrictor in the old hose) and not noticed any difference.

I agree. I ran no restrictor in the return line for years. I then swapped the rack over to a different car and had the restrictor. Rack feels the same.

OP, I think you are barking up the wrong tree as to how to change the feel.

[Carpy2]

Yeah I agree. Did some more research and testing today and it looks like the inline restrictor is more to stop foam forming more than anything. I’m still going to try and make a simple restrictor as mentioned by bluptgm3 to rule that all out. I think the e46’s system has the restrictor at the PS port instead of inline and people have replaced that with smaller diameter “restrictors” with success. Need to be careful you don’t restrict so much as to mess the system up of course.

Been looking around for more concrete info/ideas, but still can’t find much other than running an electric PS pump, and of course going to a smaller steering wheel.

[pbonsalb]

Did they change the restrictor for steering feel or foaming on the track that caused excess pressure and reservoir leakage? It does not matter whether the restrictor is near the bottom of the return hose or a few inches lower at the port. The change on the E46 just tells me it was an after thought on the E36 that was incorporated more permanently on the E46.

[NeilM]

How would a restrictor in the low pressure return line affect steering effort? For that you'd need a restrictor in the high pressure discharge line from the pump to the rack. However even that probably would not have the effect desired, or at least not just that effect. A restrictor in the high pressure line would also limit oil flow, risking the pump lagging the rack's demand for assist.

The symptom of that is random cuts in power assistance. That's sometimes seen in auto-x, where steering demand is typically for rapid back and forth movements with little or no recovery time in between. Having the rack randomly lose power assist is obviously not helpful for the driver maintaining control.

My knowledge of the finer points of hydraulic power steering system design is, ah, limited, but it seems to me that the answer lies in the rack design and its spool valve in particular. Beyond rack swaps, that's beyond our ability as owners to do much about.

I'd add that, now that the other two cars I drive have all-electric power steering, each time I drive the M3 I'm amazed at its steering quality and feel.

Neil
96 M3 — Z3 non-M rack

[bluptgm3]

There is a little talk as out fastener in our steering rack that as I understand it adjusts for wear/slop. Seems like that might offer the resistance you seek.


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[TostitoBandito]

The E46 ZHP rack I run is quite heavy. When I go to drive my M3 after driving my daily Mazda hatch for a while it almost feels like there's no power steering. Definitely heavier than stock, not sure how it compares to the Z3 rack in terms of feel. I also underdrive my PS pump, though I'm not sure that really makes any difference.

[Carpy2]

Did they change the restrictor for steering feel or foaming on the track that caused excess pressure and reservoir leakage? It does not matter whether the restrictor is near the bottom of the return hose or a few inches lower at the port. The change on the E46 just tells me it was an after thought on the E36 that was incorporated more permanently on the E46.

I agree that the e36's restrictor was probably an afterthought. I also can't find evidence to suggest BMW installed the restrictor on the e36 or e46 for steering feeling at all. However, it looks like according to this thread, on both e36 and e46 PS pumps there's a pressure relief valve that is spring tensioned. I have actually seen kits for e46's to shim this valve, relieving more pressure and lowing the effectiveness of power steering. I did not know it existed on our rack, so I'll look into this some more and see what people have experimented with so far. That thread mentions that Bimmerworld used to sell a kit for this, just a basic shim package like this from Summit racing. This thread also mentions significant increased effort from just 1 shim on e46s. Very interesting I'll keep looking into this and see if it's viable for e36's too.

How would a restrictor in the low pressure return line affect steering effort? For that you'd need a restrictor in the high pressure discharge line from the pump to the rack. However even that probably would not have the effect desired, or at least not just that effect. A restrictor in the high pressure line would also limit oil flow, risking the pump lagging the rack's demand for assist.

I honestly don't know, I'm shooting in the dark, as I have no knowledge about PS systems at all aside from how to replace a steering rack lol. There's and old thread by shogun where he mentions just replacing his old return line/restrictor increased power steering. He attributes it to newer hose = less restricting, so power steering is more effective. I was just trying to test out the opposite, and probably just getting caught up on the name being "restrictor".

Relieving pressure via the thread mentioned above just may be the ticket I've been looking for.

- - - Updated - - -

The E46 ZHP rack I run is quite heavy. When I go to drive my M3 after driving my daily Mazda hatch for a while it almost feels like there's no power steering. Definitely heavier than stock, not sure how it compares to the Z3 rack in terms of feel. I also underdrive my PS pump, though I'm not sure that really makes any difference.

Thanks for the comparison. I just ordered an underdrive kit, been on the list of things to do, and I'm interested to see a back to back comparison myself. I don't really suspect to feel much difference though based on other people's reports.

[pbonsalb]

I have a Z3 1.9 rack, solid shaft coupler, UUC UD PS pulley, etc and would still like a heavier on center feel. If you explore the pressure relief valve shim idea, let us know the results.

https://www.bimmerforums.com/forum/s...Power-Steering

[Carpy2]

I have a Z3 1.9 rack, solid shaft coupler, UUC UD PS pulley, etc and would still like a heavier on center feel. If you explore the pressure relief valve shim idea, let us know the results.

https://www.bimmerforums.com/forum/s...Power-Steering

I think I will this weekend. Thanks for linking the thread. I will report back!

[Carpy2]

Ha so I'm honestly pretty confused but I'm going with it.

When you open the PS pump it looks like this, I've drawn an arrow to the pressure relief valve. The left half of the pump is the pulley side.
Inkedmaxresdefault_LI.jpg

Once you take out the valve it out it looks like this (e46 pumps are accessed externally from the back, much easier to shim):
IMAG0111.jpg

I don't know enough from my chair to know exactly how this valve works. But it seems you add a few shims so that the valve's minimum clearance increases always allowing more fluid through, therefore releasing pressure. Sort of like running a stiffer spring. I'm assuming the more compressed the spring the higher the pressure, but could have this backwards.

[pbonsalb]

For E46M3 but maybe an idea as to the number of shims and a lead on who to search for to get more info - Volke. /http://www.m3forum.net/m3forum/showthread.php?p=1067975682

But read this:
https://www.turnone-steering.com/blo...him-kit-theory

[pizzaman09]

I recently did the Z3 rack conversion and was extremely pleased that the steering got lighter and a whole lot smoother. It's now very similar to the JCW Mini I had, though not quite as fast.

A heavier feel could probably be accomplished with some more caster in the suspension.