banks334
banks334
12/31/20 8:27 p.m.

HI, I have been working on converting a BMW 135i into a 1M/M3 which included swapping in the m3 steering rack with a much quicker ratio. The new rack is obviously much quicker and motorsport oriented; however, the rack lacks the servo-assist when retrofitted to my car. Thus, the rack is under-assisted at low speeds. I've dealt with this for the past 2 years but autocross can be a bit of a workout. So, I have been dabbling in ways to try to boost the assist. 

I took apart my pump and found that thing on the high pressure outlet are not as complex as the typical pump. I could use some help on figuring out how to modify my pump to boost the assist a bit, specifically, at low speeds like 0-30mph.

Usually you have the pressure port union, pressure control valve, and main spring. 99% of what I have come across entails modifying the pressure control valve by taking it apart and shimming the smaller spring inside of it, or removing shims, to modify the pressure relief. Like this: 

https://lh3.googleusercontent.com/proxy/8dLARSWLFI36IK5KlGp_bYsj_WNDBviqK-b3u2zDG9jcI1z4AVoCm1zVv4WMsWGTDXDUcug93M8P0nwHgSMXFo8jOQm-hl4

and it comes apart into pieces like this:

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSdQBDnYzWzSJ1Qi0M1zDuNo8YLyndS-hVMhaDhCZ-hkS9RmJHU

The pressure control valve inside of my pump is a simple plunger. There is nothing inside of it. It is hollow with nothing but a small orifice inside. So, there is nothing to modify. I suppose I can increase FLOW by boring out the internal diameter of the pressure control valve. However, that would not boost assist. So I am a little confused on how the pump works. Do you think maybe I would find a pressure relief valve if I took the pump apart? or is it just a more simple bypass?

This is what I've got:

This is the "pressure control valve" which is basically just a plunger:

This is the orifice inside of the pump housing which I am gussing I would also have to drill otu to increase flow:

And this is where I plan to modify the pump right now:

The idea would be to drop some washer down into the plunger so that the main spring is preloaded. The first washer would add 4-5mm pre-load to the spring by preventing it from sitting all the way down into it's seat in the plunger. Each additional washer would be another 1.2mm. This isn't much relative to the very long main spring. I am operating under the assumption that I can prevent pressure bypass by shimming this main spring. However, I am not sure this will help idle? I doubt there is any bypass happening at idle... 

Anyone familiar with modifying power steering pumps that can toss out some ideas? I need a decent bump at low speeds. I have 285's up front right now and it has become a but burdensome to drive as is at low speeds!
 

Streetwiseguy
Streetwiseguy MegaDork
12/31/20 10:14 p.m.

Is there a smaller pulley available?  XC90s and R model Volvo's have a smaller pulley and higher relief valve settings because heavy/big tires.

Or, can you use the pump from the car that the rack came from?

banks334
banks334 New Reader
1/1/21 12:38 a.m.

In reply to Streetwiseguy :

1M isnt exactly a common car and the pump part number is unique to it. They are pricey. I think it runs 200psi more pressure though (120bar vs 135bar). 1m/m3 also relies on "servotronic" to boost low speed assist. Retrofitting servotronic doesn't seem to be an easy feat. I thought I had it figured out but I don't seem to be getting the assist that I am supposed to. I will be revisting getting the servotronic working right but figured modifying the pump might actually be easier. 

rslifkin
rslifkin UberDork
1/1/21 10:25 a.m.

Is the Servotronic setup on the 1M on the pump or the rack?  If it's on the rack, then it works by reducing assist at high speeds, rather than increasing it at low speeds.  At least on older BMWs, the default state for servotronic when disconnected or non-functioning is minimum assist. 

banks334
banks334 New Reader
1/1/21 1:01 p.m.

In reply to rslifkin :

hmm I know someone found the data in the JBBF module to plot servotronic's curve. I'll have to dig for it but I think it did do SOMETHING at idle/low speed. I was under the impression that is why they added it to the M3 rack... to give me assist when parking etc because of complaints the M3's steering was too heavy. Yes, it is an electronic valve in the rack. I don't think I coded it correctly so i don't think I am getting a signal. I am going to test to see if I am getting voltage to it tomorrow. 

Still looking into a more manual solution though. I got some better light down into the higher pressure outlet and I am guessing that thing at the bottom is actually like a "built-in" pressure relief valve. looks like it's pressed into the pump housing and sitting at the bottom of the port. I might try to disassemble the pump to see what I find.

I have read that modifying the bigger main spring isn't recommended but this was only said within the context of having the ability to modify a present pressure relief valve spring. I can't find anyone who has modified the main spring. I want to say the steering is a bit lighter after shimming the spring but I'd need to go back in and make a more drastic change to really tell a difference... Maybe tomorrow I'll add more shims.

Slippery (Forum Supporter)
Slippery (Forum Supporter) GRM+ Memberand UltraDork
1/1/21 1:24 p.m.

I second changing pulleys. All my BMWs have removable pulleys. I would measure the diameter and try a different size. Only drawback is that it will modify the low speed and high speed assist. 

I can help you with measures from S52, S54 and S65. Just sold my M4, so that's out. 

rslifkin
rslifkin UberDork
1/1/21 1:34 p.m.
banks334 said:

In reply to rslifkin :

hmm I know someone found the data in the JBBF module to plot servotronic's curve. I'll have to dig for it but I think it did do SOMETHING at idle/low speed. I was under the impression that is why they added it to the M3 rack... to give me assist when parking etc because of complaints the M3's steering was too heavy. Yes, it is an electronic valve in the rack. I don't think I coded it correctly so i don't think I am getting a signal. I am going to test to see if I am getting voltage to it tomorrow.

If the M3 pump has higher output pressure, it's quite possible that the 2 go together.  Higher pressure to get more assist, then the Servotronic to reduce assist at high speeds to prevent it from becoming excessive. 

banks334
banks334 New Reader
1/1/21 2:06 p.m.

In reply to rslifkin :

I think I just confirmed that my stock pump is 135 BAR same as an M3/1M. So, no "pump swaps" to really take advantage of even if I did want to fork over $400 for a 1M pump...

Also, here is the servotronic data that was found using NCSDummy:

The valve is getting more current at idle. Not sure if that means more or less assist but that's the curve supposedly. I am pretty sure it's more assist at idle to help low speed manuevers and parking with the sportier alignment and tire setup the M3/1M got.

 

 

rslifkin
rslifkin UberDork
1/1/21 2:13 p.m.

More assist at idle makes sense.  Being that the pumps are the same, I'd say there are a couple of possibilities:

  1. The M3/1M racks are designed to produce more assist from the same pump and use servotronic to reduce the assist at high speeds to avoid it being too much
  2. The M3/1M steering isn't actually boosted any more at low speeds, it's just boosted less at high speeds. 

In either case, the servotronic valve likely reduces assist when not powered, so you're currently at minimum assist.  Powering the valve will increase the assist by flowing more fluid, although it's unknown whether that'll give more assist than the original 135i setup or just the same.  I know that's how the system works on the steering box in my E38. 

banks334
banks334 New Reader
1/1/21 2:15 p.m.

In reply to Slippery (Forum Supporter) :

I just measured my pulley to be ~119mm diameter and ~26mm belt width. Stock belt is a 7PK V shaped belt. Any help on a decent pulley to try to swap on would be appreciated! I am not so sure I want significantly more assist at speed but I'll give it a try. Steering feels great at 100mph lol. I'd be willing to swap pulleys for autocross and track days though! doesn't take much work.

banks334
banks334 New Reader
1/1/21 2:24 p.m.

In reply to rslifkin :

OK makes sense I think... so if I can get the valvetronic valve working I'll be getting full flow through the rack as intended. Then the "curve" of the valvetronic actuation is actually applying less current to the valve to reduce the assist at high speeds. Without current applied to the valve I am just always in that state of minimum possible assist.

I do think that I did not retrofit it correctly. I will be rechecking my coding and wiring.

I don't know why the 1M got a special Bosch power steering pump... Might just be a more premium pump? The 1M has the same N54 engine in it as a 135/335i that got a LUK pump. The M3 has the S65 so that 135BAR pump is actually different... but the 1m/135i pumps seem identical other than brand. Maybe they have a slightly different output curve to them or something. Different vanes or something who knows.

This makes me think though... that if the servo is closed since no current is applied to it then my pump IS bypassing a lot at idle. Maybe shimming the main spring will work if I add more shims. Why does this have to be so complicated lol. 

KyAllroad (Jeremy) (Forum Supporter)
KyAllroad (Jeremy) (Forum Supporter) UltimaDork
1/1/21 3:01 p.m.

Different car, but a friend of mine let me co-drive his highly modded Malibu a couple years ago.  First run I realized his power steering was problematic.  It gave good assist but the orifice inside the pump was too small and on rapid transitions you'd overcome what the pump could supply and nearly lock up the steering (on 315 Hoosiers!)

He replaced the orifice in the pump for the next event and the car was 100% better to drive.   I'd try the simplest solution first.  Allow more fluid to flow through the system.

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