E85 Steering rack issues - hard to resolve

[ryushe]

I need to vent a bit, and am requesting some input here.

I've got an '04 (made on 15/12/2004 to be exact) 2.5 E85 LHD. Somewhere last year my car started developing issues with the steering wheel while driving at highway speeds. Between approx. 100 and 135/140 kph the steering wheel will start to wander around and move left-right, making it a most uncomfortable drive as I'm constantly having to correct. Below or above these speeds everything is alright; the car still feels direct and tracks just fine.

Anyways, since this started happening, I've had the car fully aligned (just in case, but no issues there), had it in for a diagnosis (unresolved), had my rims checked to see if they were crooked in any way, replaced bushings, and as per suggestions on this forum played around with the adjustment ring for the EPS motor (no dice). None of these have had any effect, and the latest diagnosis as of last week is that there's an issue with the steering rack, in particular with there being some play in the gears at the point of translation of steering column to the rack itself.
We've pretty conclusively ruled out any sticky steering issues as well.
Edit: I'm running Michelin Pilot Sports, no runflats.

The above took me quite a bit to figure out, and sounds to me like a 'minor' issue; getting a new steering rack can't be hard right? Well, it is.

Turns out BMW can get you pretty much every single part for an '04 E85, but for some bizarre reason they no longer provide steering racks . Rebuilding a steering rack is something that seems impossible in this case, as all companies that do revise/rebuild steering racks say they change a few seals, lube the thing back up, and Bob's your uncle, but they don't touch the gears themselves.
Trying to find a second hand steering rack is also proving completely fruitless. I found two, but both were from high mileage Z4s (220.000 km+) and one of them had also been in a frontend collision. There also don't seem to be any aftermarket steering racks for the Z4 either.

In other words, it seems like I'm screwed and I feel I've run out of options, besides simply living with it and hope the play in the gears doesn't increase. But that seems hard to accept. I love the card, and there has to be something that can be done.

So question, how have others here dealt with this? Is there something I'm missing? Why is it so damned hard to find a replacement LHD steering rack?? Are there other options outside of retrofitting an E46 hydraulic (see: https://www.bimmerforums.com/forum/show ... c-Steering)?
Anything?

[Mike6]

Dont think you mention tyres in your post. If you have runflats could that explain your issue.

[bigwinn]

Aye tyres would be first stop to see what you are running

[ryushe]

Will amend post, but I'm running Michelin Pilot Sports. Got rid of the runflats pretty much the day after I got the car

[enuff_zed]

From past experience of much older cars, symptoms where it only happens between certain speeds often came down to bushes.
At lower speeds rolling resistance pulls the bush tight in one direction, at higher speeds aerodynamic forces do the same, but there is a spot in the middle where the loads balance out and for a short window the bush is very lightly loaded.
My old Capris used to suffer exactly this if the inner track control arm bushes were worn.
Now I know you say you've done the bushes, but I have read somewhere that failing RTABs can cause an element of rear wheel steer.
Have you changed them?

[j3nks79]

Have you checked/changed
Front arms and lollipop bushes?
Inner tie rods and track rod ends?
Rear trailing arm bushes?

[ryushe]

Now I know you say you've done the bushes, but I have read somewhere that failing RTABs can cause an element of rear wheel steer.
Have you changed them?

That's a good point, I have not. New bushes were fitted up front for things like control arms etc. Should I be able to feel anything like play or movement with the rear wheels when off the ground? Either way, it's another thing to try out.

That being said, if it still is the steering rack, any options there that anyone can think of?

[ryushe]

Have you checked/changed
Front arms and lollipop bushes?
Inner tie rods and track rod ends?
Rear trailing arm bushes?

Checked:
- Yes
- Yes
- No, but that is a good suggestion.

Enuff_zed mentioned RTABs as well. You guys are the first to suggest this, as the techs that have looked at this (3 shops by now! ) are all convinced it's the steering rack.

[j3nks79]

When rear trailing arms are bad you will feel the car wandering around at motorway speeds. When they are really bad you think the back end is going to step out

[ryushe]

When rear trailing arms are bad you will feel the car wandering around at motorway speeds. When they are really bad you think the back end is going to step out

That's the thing, it's not the car itself that's wandering around or juttering, it's purely the steering wheel. Car itself is pretty much laser straight when driving at those speeds...
But will check!, thanks!

[enuff_zed]

And just to add to your confusion, how old are the shocks?
Worn front ones could possibly not keep the front wheels in touch with the road, and again aerodynamic forces on the bonnet could influence this.
Rear ones could let the rear dip, therefore the front rise, and the front end get a bit light.
Do you have spacers on the front?

[ryushe]

And just to add to your confusion, how old are the shocks?
Worn front ones could possibly not keep the front wheels in touch with the road, and again aerodynamic forces on the bonnet could influence this.
Rear ones could let the rear dip, therefore the front rise, and the front end get a bit light.
Do you have spacers on the front?

Shocks are 3 years old give or take. No spacers.
With regards to 'not keeping the front wheels in touch with the road', I expect I'd feel that in driving in a straight line with the car wandering around. However in a straight line it drives perfectly fine. It's purely the steering wheel that's acting up.

[inkey$]

Long shot, but could it be the EPS motor itself? I know you said you'd adjusted it, but if its failed or failing, then would this not create the sticky steering/wandering-jitter-at-speed effect too?

[ryushe]

Long shot, but could it be the EPS motor itself? I know you said you'd adjusted it, but if its failed or failing, then would this not create the sticky steering/wandering-jitter-at-speed effect too?

That was our first thought, as it almost seems like the EPS motor is 'self-adjusting' the upper steering column at those speeds. If you've ever driven a car with lane assist, it's almost like that, but where lane assist is relatively slow and gradual adjustments, this happens a lot faster and only impacts the steering wheel and not the drive itself.
However, the EPS seems to check out. This also gave us the idea that it might be related to the ABS/speed sensors, as if it IS an electronics issue, it's seemingly speed related and could possibly be due to faulty input data. Sadly the sensors check out fine too (checked by fitting replacements as a test and comparing between original and new sensors).
I've also thought about a faulty steering angle sensor, but from what I gather it doesn't directly interact or send data to the EPS motor. Also, replacing that is a pita.

Either way, 3 independent BMW specialists in NL have assured me it's the steering rack, hence the original question. I would love for them to be wrong though, as getting a replacement is turning out to be quite an adventure, and expensive too if I could even find one...

[bigwinn]

Worth biting the bullet and going hydraulic?

I think I budgeted £200 ish in parts and doing the works myself?