Looking for advice on steering/suspension issues

[pauliebuttons]

Hello fine people of the forum - I'm having a few issues that I'd appreciate some advice/validation on. I'll preface this by saying I'm pretty practically minded, but also inexperienced on working on cars. However I bought this Z4 to learn a bit more how to do this stuff, so lets get stuck in:

Currently my 2007 Z4 Coupe doesn't drive straight. It's constantly pulling to the left, and feels like it's maybe slightly easier to turn the wheel left than right. On top of this, it feels very nervous over uneven roads. I thought this was an electric steering thing, but I also own a Mini R56 (also with elec steering) and while that will break your spine going over a manhole cover, but it will keep driving straight and true. In the Z4, you really feel the bumps through the wheel and it's just not a confident driving experience. Edit: There's also sometimes some very slight front-to-back rocking/occilation over the small bumps you get between tarmac sections on the motorway.

So my first step in this journey was a 4 wheel alignment - it was very slightly out (the tech said that if anything, that alignment would pull to the RIGHT), so I got it fully corrected anyway and needless to say, no difference. (I noticed when I got home it was set up to a E89 spec, but some forum searching says that's not an issue, that would be causing this current problem anyway - feel free to correct me!)



So I'm thinking now, it's either
1) A mechanical issue. It's a high mileage car so something somewhere could be worn out.
2) It's a weird electric steering issue, like a failed calibration sensor or something?

I've thought a lot about Number 2 but I have no warning lights and I don't think it's related to the sticky steering issue, so Number 1 seems more likely.

Thankfully the previous owners left a stack of documentation to go through:

Rear suspension was refreshed by PO ~5k miles ago with new Bilstein B4s and Suplex springs. I can't find any evidence of when the front was last done.

I got under the car and the front does look pretty tired. I found a 2024 receipt for anti-roll bar links but I don't believe they were ever fitted as these look quite old. Also my steering knuckle looks like someone picked it off the deck of the Titanic.


I have a 2018 receipt for a new Meyle control arm kit. These do look pretty new and the rubbers visually look not too bad:


I'm thinking it's probably worth refreshing the whole front suspension anyway. It's a weekend car that I'd like to take on track days without compromising too much on road handling, and could be a good opportunity to learn stuff.

Options seem to be:

A) Find a matching front set of B4s/Suplexes and put in new drop links/ARB bushes? while I'm at it.
B) Go adjustable coilovers so I can set it soft for the road, firm for the track. Currently favouring BCs although I'm confused about what spring rates to go for.

My worry is dropping £1k on coilovers and not fixing the underlying problem. Is there anything else I should be looking at first?

 

[Zedebee]

A lot of Z4 “steering issues” can be fixed by changing the tyres. The OEM Bridgestone runflats are truly awful. If fitted, swap these for almost anything else immediately, but preferably a premium branded, non-run flat.

Also, steering is particularly sensitive to tyre pressure. Make sure yours are inflated correctly on both sides.

The steering knuckles do get rusty, but are pretty solid. They are very rarely an issue, and a good wire-brushing will save you the cost of replacement.

The steering control arm ball joints can get loose. They are non-repairable, so you may need new control arms. Not too difficult or expensive. The lollipop bushes (where the control arms attach to the car) also wear out.

It’s definitely worth replacing the front suspension - top mounts, dampers and drop links. The dampers last up to about 40k miles and if they look knackered they probably are. Won’t make a massive difference to your steering, but the car will ride and handle a lot better. This is your opportunity to fit coilovers.

Finally, it’s unlikely to be a steering calibration issue. I have never heard of this being an issue. It is worth noting that the Z4 electric steering has never been great and part of what you are experiencing might just be normal.

Good luck getting it sorted.

 

[pauliebuttons]

I knew there was something I forgot to add - currently running Pilot Sport 2s on the front, Vredestein Giugiaros on the back. All look like they have loads of life left. All inflated the same, off the top of my head I think 34 PSI.

 

[pauliebuttons]

Updates!

Went down the B4 route - got new top mounts and droplinks too. Got a local garage to assemble the shocks for me at £30 a pop.

Right side went on ok, although no thanks to that headlight angle sensor. I think this was an original BMW shock and it was pretty knackered:



Left side I tried doing today and ran into some findings, and some issues. First thing, its definitely been replaced before as this was not a BMW original:



Also the top had this crack in, which might be part of my problems:



And under the tower looks like this. Seems to be some welding/torching done, anyone care to guess what's going on here?:



Unfortunately this is where it all went off the rails. I got the new shock in, but didn't align the top mount properly so the 4th hole doesn't line up - s**t. Then it gets worse: 2 of the nuts just won't do up, and they won't undo either! 2 of the top mount studs must have come out, and i'm really stuck on how to get them off.

I'm now thinking the torch marks has something to do with this. When I took the old shock off, 2 of the studs immediately fell out. I didn't even know they came off at all! Maybe someone in the past had this problem and tried to torch them off?



So now I'm looking at calling up the garage and asking them to drill/cut the studs off and getting a new top mount - unless anyone here has any bright ideas?

 

[enuff_zed]

That looks like someone has played about in the past.
Basically moved the top mount holes inboard to get more camber.
That is well out of line looking at the last photo.
Don't want to worry you too much but after all that welding etc, I'd be wondering if you may need to cut out the strut tower and get a new one welded in, properly measured.

On another note:- I bought a proper hydraulic spring compressor. Take about five minutes to strip and rebuild a strut now. I thought I was being cheeky asking peiople for a fiver each side! Sixty quid!!! For maybe fifteen minutes work? Jeez!

 

[pauliebuttons]

The alignment might also just be me not having the top mount rotated round the right way. Unfortunately can’t get the damn thing off to rectify my mistake.

Oh yeah and the top nuts got like that with me just ratcheting them on - was on my best behaviour not over-using the impact gun, honest!

I also noticed the tie rod end on this left side has a big R stamped on it - so definitely been fun and games on this corner before…

 

[pauliebuttons]

Update time:

• So new B4s and springs all on - got the garage to fix my nut threading problem (they've done well out of me for this adventure).

• New top mount on the side I messed up

• Reinforcement plates on both sides.

• Garage confirmed I had swapped around tie-rod ends, and both looked quite old so I asked them to put brand new ones on.

• New (basic) alignment.

Result:
Actually drives in a straight line now!

Definitely rides the bumps better, settles faster and no longer rocks back and forth. Still had the nervous fidgety steering issue though. So this afternoon I had a good long read of the 'steering fix' thread, and dove into the footwell to have a look and found the telltale pen marks that someone's done this job before! So on a hunch, I slackened the bolts and rotated it about 5mm back to make those pen marks line up, assuming that would bring it back to 'factory' settings

What a difference! The steering is noticably lighter driving at slow speeds, and then on the motorway it's so much smoother. Now it doesn't feel like it's trying to pull the wheel out of my hand over every bump. I gave it a good hour's drive just to check the previous 'steering fix' wasn't obscuring another issue, but all seems fine. I'm guessing my change has ended up increasing the power assist overall, may have lost some of the 'feel' but it's way less nervous.

I'm really happy, it now drives more comfortably and predictably, and how I think a Z4 should drive. Next on my list, CDV delete.