How To Increase The Power Steering Feel/Pressure

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Philo
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How To Increase The Power Steering Feel/Pressure

Post by Philo »

Last month I put in a new PS pump because the old one was groaning a bit. I really thought I was going to get a bit more pump pressure and lighter feel on the steering wheel.., but it was not to be. So, now i'm in pursuit of how to get a pump to put out more pressure and see if anyone has been down this road before.

I've read a bunch of post here about the heavy steering feel of the E28, and personally I'm ok with it in general, have been for about 20 years :) But since I put on some new shoes the steering is just a bit too stiff around parking speeds and would like to fine tune it if possible.

Here's the details
* S54 swap car running E46 M3 PS pump.
* E46 reservoir and filter.
* CHF 11s for the fluid.
* Stock E28 M5 steering box.
* BBS 17x8.5s with new Michelin Pilot Sport rubber.

I have the old pump and I'm ready to rip it apart. I've been told that if I change the PS pump's internal valve spring slightly, shim it to limit the bypass, it will allow more pressure to go through the system and hence give a bit more power steering feel.

Has anyone done this before on a BMW power steering pump ?.., or with any other type of pump ?

Lastly, all PS related systems are working perfectly, no clogged lines or filter, the belt isn't slipping, steering box is in great shape, idle speed is 900ish, etc..

Thanks in advance.
tn535i
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Re: How To Increase The Power Steering Feel/Pressure

Post by tn535i »

I've gone the other way around on an e30 and put in a weaker spring (or we used a pump with weaker spring to begin with) to lower the pump pressure to give more steering feel so I know it is possible. I don't recall exactly because we had two or three pumps to take apart and choose components from. We also put a quicker e36 rack in the e30.

Somewhere my son and I did some research and found the output pressures of the various pumps. It might be right there on the parts listings of BMWfans, etc. In your case I am going to guess the pump you have is set up for rack and pinion and runs lower pressure than a typical e28 with recirc ball and hydroboost. The pumps I think are all very similar in design so may be no more difficult that shimming the spring or getting a stiffer one from another pump.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

So I took the old pump apart and boy these things are simple, nothing flew across the garage when I took it apart, lol... Within the the main chamber where the vane pump rotor is located there's really nothing that can be modified. I think the area I need to focus on is the pressure orifice that the high pressure line screws into. There's a groove and hole that no doubt regulates the pressure along with the spring that sits under this part.

I'm not 100% sure if I need to put a stronger spring (shim it) or weaker spring in place to increase pump pressure. My concern is if I increase spring pressure will the system bypass properly when at full L/R lock. I also read on a non BMW board that we can drill out the orifice hole on the high pressure pin to increase pressure but not sure I want to do this, yet..

http://phil.infostreet.com/M5_Images/PS ... 093130.jpg
http://phil.infostreet.com/M5_Images/PS ... 093140.jpg
http://phil.infostreet.com/M5_Images/PS ... 093150.jpg
http://phil.infostreet.com/M5_Images/PS ... 093207.jpg

Open to thoughts.
tn535i
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Re: How To Increase The Power Steering Feel/Pressure

Post by tn535i »

I think that's a little different set up than I remember on e30 pumps and I have assumed e28 pumps similar but never had one apart, but you have an e46 pump there I think?

You will need to study the passages in the casting. I would guess pump pressure pushes against the end of the spool valve at all times trying to move it against the spring. The pump flow is passing into the relieved area of smaller diameter in the middle of the spool. Form there it can pass to an opposite port or through the hole in the spool to a second port more or less in the chamber where the spring is. I guess that chamber goes to the steering box. But the displacement of the spool due to pressure changes alters the porting and area for fluid to flow around the bypass from the outlet of the pump back to the inlet. So when pressure drops that port closes as the spool moves sending all it can to the steering but when steering is satisfied the spool opens the bypass keeping the steering pressure more or less constant. So it tries to maintain pressure and flow out of the pump whenever pressure drops by closing the bypass and whenever pressure goes back up it opens the bypass.

I hope that makes sense. So then in your pic 3 is that threaded part the thing that holds the spring and spool valve in place? If it is just a cap over the spring it makes it really easy to pull the spring and replace or shim to try it out different pressure. Shimming with metal O-rings or narrow crush washers would be the easy way to go if you can get them. Maybe an oil pan or diff washer is close?

I am totally unsure if a recirculating ball e28 steering box demands more or less fluid flow when turning than an e30/36/46 rack. That could mean the pump just can't deliver the flow you need even if the spool send everything it can to the steering. Hopefully it is capable as my guess is that recirc ball needs higher pressure but less flow and r&p needs more flow at lower pressure. But IDK.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

Over the weekend I pulled the pressure valve and spring out of my LUK LF30 PS pump and found that they updated the pressure valve design. There is only one large spring now vs. a two spring setup. It's really hard to describe the new design and failed to take pictures. Sorry about that. The new bypass setup does not use the BB and seat design. If I can find pictures online I'll post them.

The bottom line is I put a .040" washer/shim under the base of the spring to add a bit more pressure on the bypass valve and it worked like a charm. Didn't even have to pull the pump off, just removed the hose, let it drain, then unbolted the big nut that holds the pressure valve in and then pulled the spring out.

Thanks for all the tips and help with this. I might go .060" later on but just wanted to report that there is a noticeable difference in steering effort. And, the steering box feels tighter as well. Wonder why this is ?? Maybe the recirculating ball type of box requires a specific minimum ideal operating pressure

Thanks again.
Mike W.
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Re: How To Increase The Power Steering Feel/Pressure

Post by Mike W. »

Interesting, .040 made a noticeable difference. No use to me now, but something to file away for the future.
tn535i
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Re: How To Increase The Power Steering Feel/Pressure

Post by tn535i »

Philo wrote:Thanks for all the tips and help with this. I might go .060" later on but just wanted to report that there is a noticeable difference in steering effort. And, the steering box feels tighter as well. Wonder why this is ?? Maybe the recirculating ball type of box requires a specific minimum ideal operating pressure
Could be that and could be the spool valve in either a R&P or RB takes a little effort to overcome and is designed for specific pressure. The sooner it opens the sooner you get assist or in the case of higher pressure it takes a smaller opening to get same assist as a larger opening with less pressure and flow.

One of the mistakes some people make is thinking they can eliminate the power steering on something like an e30 R&P. It just leaves it vague on center because you still have the spool valve spring letting it wiggle back and forth.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

Thanks everyone. Drove the car to work again, 100 miles round trip, and the steering is definitely lighter in the hand but still a bit heavy negotiating around parking lots. Gonna go from .040" to .060"... or should I do .080" ?? Will also buy a banjo fitting so I can check the line pressure to the steering box. We should be at 130 bar at deadhead reading, right ? Not sure what fitting to buy though, pressure fitting banjo block thingy maybe ?.. will dig around on da-google.

Thanks !
Gatso7
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Re: How To Increase The Power Steering Feel/Pressure

Post by Gatso7 »

Pump Pressure:
Idle.. 110 bar
driving.. 120 bar

Per the tech manual.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

Thanks Ben, do you see what they call a "deadhead" pressure spec. This is when you turn the wheel to it's max and hit the stop.
Gatso7
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Re: How To Increase The Power Steering Feel/Pressure

Post by Gatso7 »

Philo wrote:Thanks Ben, do you see what they call a "deadhead" pressure spec. This is when you turn the wheel to it's max and hit the stop.
No..that was all the info.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

So I've been working on this issue lately. My first spring shim was .040" and felt a slight difference. So I added another .040" shim and now the steering is much better. I still can't do a low speed-hard turn into a parking stall with one hand though. So will add maybe .020" more and then hook up a pressure gauge and see where the pressure is at. During this exercise I find it interesting that the PS pump for the S54 rack & pinion, that has a similar pressure rating as the M5 pump, feels so different when on the car. I have a feeling the pressure rating on pumps is at full lock and not when at rest or under slight turning load. Must be a completely different pressure curve.

Fun fun...
cek
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Re: How To Increase The Power Steering Feel/Pressure

Post by cek »

Subscribed because this will be valuable to me in about a year when my S54 car is on the road and I discover it's hard to steer and I search and find this thread.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

Cek, how's the build coming ? May want to consider a rack swap since the car is apart. Then the PS pump on the S54 should be a good match.
cek
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Re: How To Increase The Power Steering Feel/Pressure

Post by cek »

Philo wrote:Cek, how's the build coming ? May want to consider a rack swap since the car is apart. Then the PS pump on the S54 should be a good match.
I've not seen a rack swap that actually worked...
tn535i
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Re: How To Increase The Power Steering Feel/Pressure

Post by tn535i »

cek wrote:I've not seen a rack swap that actually worked...
An e36 rack into an e30 is a wonderful thing, with easier/better tie rods to boot. But I'm with you on an e24/28 as I'm not sure you'd be able to ever put it where it belongs. I think you would have to carry over the subframe from the other car and modify the suspension.

I can imagine an S54 in an e28. It would be one (or two) more steps up than the difference between the M6 and the 535.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

Hey!.. I'm reviving this discussion because I decided I need easier power steering after turning 60 :) ... Kidding a bit, I'm pretty fit, but the steering feel is pretty heavy at slower speeds and would like to fix that.

First, I have a question about the original hydroboost booster/PS system I had on the car prior to swapping in the S54 and going vacuum boost. So the question, does the original hydroboost system only supply hydraulic fluid to the power steering pump ? Or does it indeed assist the steering box? Sorry, I know this is an obvious question but I've been away from the old hydroboost system for so long I can't put the mechanical parts together in my head.

Having said all this I found a great diagram on the Big Coupe board and it looks like the hydro system does supply pressure to the steering box, or am I wrong and the fluid simply passes through the hydroboost's regulator body and then to the steering box? If the hydro system does supply fluid pressure to the steering box how is steering assist accomplished on a vacuum system like the 528e. By the way, I'm running the 528e vacuum booster so you can guess where I'm going with this post.

Hope I'm not talking in circles here, sorry if I am. Below is the E24 hydroboost diagram. I looked for a diagram for the 528e vacuum system but haven't found anything yet that explains the above. Thanks for the help.

Image
Mike W.
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Re: How To Increase The Power Steering Feel/Pressure

Post by Mike W. »

If I'm reading it right, and I may or may not be, the "flow control piston" minimizes or cuts off pressure to the steering if pressure drops too low so as to keep pressure going to the brake booster. I guess stopping is more important than steering. That might also be the reason I had to have the PS pump belt super tight on my 535i to keep PS in the rain and wet. I'm thinking I wasn't necessarily losing pressure entirely, but any loss of pressure would result in losing power assist on the steering.

But I think you're going in the wrong direction. I don't think pressure is the problem. I recall an article long, long ago in C and D about steering feel in a Camero or something. It spoke about a spool or torsion spring or something in the steering box that had been changed and resulted in much greater feel and somewhat less boost. Suggesting you're going to have to tweak something in the box itself to lighten steering effort. Now back in the 70's a friend of a friend had a racing power steering business/factory. Sun Valley/Van Nuys, somewhere around there. I'm sure it's long gone, but that might be the sort of place you need to talk to to figure out how to lighten the steering.

On a related note, I'd been thinking about you last month, meaning to contact you. I recall you'd been looking at some length on how to put a rack and pinion steering in your car. Up in Reno at Eric's Reno Fest there was such a beast, a R and P E28. I asked the guy and he acted like it was old hat and everyone had it, but said it was an E46, RHD rack, flipped. Like sure, everyone's got those laying around.
uzayas
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Re: How To Increase The Power Steering Feel/Pressure

Post by uzayas »

I have this diagram for E28

Image
gadget73
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Re: How To Increase The Power Steering Feel/Pressure

Post by gadget73 »

Mike W. wrote: Oct 12, 2021 2:07 AM

But I think you're going in the wrong direction. I don't think pressure is the problem. I recall an article long, long ago in C and D about steering feel in a Camero or something. It spoke about a spool or torsion spring or something in the steering box that had been changed and resulted in much greater feel and somewhat less boost. Suggesting you're going to have to tweak something in the box itself to lighten steering effort. Now back in the 70's a friend of a friend had a racing power steering business/factory. Sun Valley/Van Nuys, somewhere around there. I'm sure it's long gone, but that might be the sort of place you need to talk to to figure out how to lighten the steering.
.
The torsion spring affects how fast the spool valve inside the rack or steering box moves towards the "assist" position. A softer one gives more boost.
If you ever open one up its reasonably easy to figure out what the part is, figuring out what spring to change it to is on you though.

https://theengineersjunction.blogspot.c ... ciple.html

Too much pressure in the system can cause problems with seals failing. It might give more overall steering assist, but the amount you get relative to wheel position won't change. If you haul it over fast it will boost like crazy but small inputs will still be about as heavy as it ever was. The exact shape of the valve also affects this but changing that is well beyond what most folks can actually do.
adam_poll
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Re: How To Increase The Power Steering Feel/Pressure

Post by adam_poll »

On a 528e or any other vacuum assist E28 the high pressure line from the pump goes directly to the steering box, when I converted my car over to that booster I just used a 528e line to accomplish that. Very straight forward.

This thread has information about the various racks in 3 series and Z cars but it also talks about reducing system pressures for more steering feel/effort, it might give you some insight into what you want to do and how to accomplish it to do the opposite.

https://nam3forum.com/forums/forum/main ... ion-thread

On the note of rack and pinion conversions this is something I have been thinking about lately and might make a move on soon. I took measurements from a 6 cylinder E39 in a local yard, the racks have 150 mm travel (5.9") and are 3 turns lock to lock so pretty much the same as the faster E46 rack in that sense, inner tie rod distance on the rack is about 25". I'm wishing now that I had measured an E46 just to see if it was any narrower. The E28 measures about 6 3/4" stroke (but in an arc) and 22" with 3.5 turns lock to lock, these racks will give a slightly faster effective rate of 3.375 turns lock to lock but the reality with the shorter travel it will be 3 turns and less overall steering angle. How the inner tie rods being moved 1.5" will effect ackerman etc I am not sure yet but I think I am getting close to ordering a RHD rack (probably E39) over the winter to play around with. It looks like the connection to the steering column might be pretty straight forward (possibly plug and play) and then it is just a case of fabricating mounts and figuring out what off the shelf lines will work at least for the high pressure side.

There are many other rear wheel steer racks out there and some even with center take off (early 2000 civic as an example) but I'd prefer to keep it in the family, hopefully that makes it easier overall. It seems like finding a rack with over 6" of travel is tough and didn't see anything in that range going through the u-pull yard. I thought a first gen Mini might be the answer as they are rear wheel steer with a very quick ratio (under 3 turns) but the stroke on those seemed to be around 5" so no good, leter Mini's use electric assist at the rack and will not fit (still have the stroke issue).

Goal for this, better steering feel, slightly quicker steering if I can get it, a power steering system that can keep up through an autocross slalom (current box can't) and no weird side affects of the swap (screwed up ackerman, bad bump steer) so we will see.
Philo
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Re: How To Increase The Power Steering Feel/Pressure

Post by Philo »

Thanks for all the great info guys. We decided to try the E39 pump that has a bit more pressure than the E28 pump. So far, seat of the pants, there isn't much of a change and the steering remains a two-hander around parking lots. I also have a leak in my box that pre-existed putting on the E39 pump. Anyone have a line on a seal kit, they are NLA according to BMW.

Another thought I had was to try a servotronic box but have no idea if this is feasible.. Anyone know ?
cek
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Re: How To Increase The Power Steering Feel/Pressure

Post by cek »

Philo wrote: Oct 14, 2021 4:27 PM Thanks for all the great info guys. We decided to try the E39 pump that has a bit more pressure than the E28 pump. So far, seat of the pants, there isn't much of a change and the steering remains a two-hander around parking lots. I also have a leak in my box that pre-existed putting on the E39 pump. Anyone have a line on a seal kit, they are NLA according to BMW.

Another thought I had was to try a servotronic box but have no idea if this is feasible.. Anyone know ?
I let Kohler drive Minerva (S54 PS pump and M5 box) in Reno. I drove his 535is. I commented to him how heavy his, Vlad's (535is), and Maytag's (528e w/ M5 box), steering felt compared to Minerva. He suggested the E46 S54 pump was 'over pressuring' the E28 system, hence the lighter feel.

You might want to try an E46 pump...
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