Terrible handling – (now a lot better)

In advance - I'm not sure of the exact name of each of the bushes in the rear suspension setup - but if your referring to the joint that links the rear upper arm to the hub, then the below applies...

Pictures describing here - https://www.pistonheads.com/gassing/topic.asp?h=0&f=47&t=1755842&i=63

The top joint is a ball joint. You would expect to be able to twist it from side to side - although the spring, and especially the ARB, will try to deflect this to the extend that you might not be able to.
I used a breaker bar for leverage to try to ascertain if there was any play in the ball joint, but couldn't detect any.
Only once the ball joints were removed could a small amount of play be detected - it's just too difficult with the way it's all connected.

In addition, my last car (MG ZT) used an identical rear suspension setup. The above ball joint wore out such that it was completely destroyed. I don't remember noticing any differences, before, during or after the repair.

EDIT - They are a bit of a faff to change, but they are £10 each. So you could do the entire rear axle, including upgrading the standard lower bushes for M3 / Z4M spec ball joints, for a little over £40.
 
Thanks Jakg that's very helpful - I't hadn't occurred to me there was a ball joint there. I took a video but can't upload .MOV files from an iPhone here. It is does twist pretty easily. I doubt the ball joint will be a problem but I do wonder if wear in the inner bush would be enough to cause the apparent bump steer I'm experiencing.
I'm up for most jobs but don't have much in the way of bearing removal tools and don't want to be stuck with the car on my drive but one of the bushes stuck because my improvised kit isn't man enough so I'll probably let someone else have the pleasure. I'm feeling a bit silly that I didn't get these bushes done when they were replacing the control arms. May have been a bit more access if nothing else.
 
Quick update - since last post I've had the rear upper wishbone bushes (inner and outer) changed. So that's all bushes (apart from subframe and engine) refreshed. The garage also altered the damping on my KW's and very carefully set up the alignment so it is bang on for a z4M. I can now report that the very different turning left vs. turning right appears to have been resolved (which is a significant relief). However, I still have the underlying terrifyingly erratic steering. The car feels OK in a hard turn but around dead centre on a motorway I'm constantly working because it's twitching one way then the other. I've just driven back from Manchester via Sheffield to St Albans) and I feel like I've been in a boat all day! This is not the classic tramlining. I've done 70,000 miles in this car and experienced all of the RFT/Spring etc. etc. issues this is new(ish).

I wonder if the problem is partly to do with the power steering. In a fast (motorway) bend (i.e. just off driving straight) it's a bit like driving a van in the wind. It sort of grabs it a bit (as tho. the power steering is trying to help) then relaxes, then does it again. The thing, is I'm not really feeling it through the steering wheel but its very obvious sitting there. On the small bit of my journey I did off the motorway I turned the traction control fully off (I normally only do the first stage) and pressed the Sport button (which I never bother with) and my perception was it was a possibly a bit better. There has been so much slow traffic and roadworks it was really difficult to consistently define exactly the conditions and systems (other than always bad). I think the Sport button reduces the amount of PAS assistance?

Given that literally everything else has been checked and rechecked - could the symptoms I describe be consistent with 'sticky steering' or perhaps another electronic/system issue? I think there was something about centering the sensor for the EPS?
 
You say, you have different tyres on front and rear.

I was experiencing similar symptoms as you describe. Went away completely when I changed to 4 new tyres - all of the same type. Goodyear’s in my case. I don’t think these cars like mix and match

I also dropped the pressures and am currently running 34 32
 
It does have different tyres front to rear although all are in good condition. I am mindful of this as a potential problem but I have to say in the past when I've swapped Bridgestone Potenzas to Conti's and then later to non-RFT's (and then to staggered) mixing tyres across the axles has not been an issue like this.

i read something before about pulling the fuse for the power steering. I think I might have a go at that and see whether it makes any difference.
 
Newbers said:
It does have different tyres front to rear although all are in good condition. I am mindful of this as a potential problem but I have to say in the past when I've swapped Bridgestone Potenzas to Conti's and then later to non-RFT's (and then to staggered) mixing tyres across the axles has not been an issue like this.

i read something before about pulling the fuse for the power steering. I think I might have a go at that and see whether it makes any difference.
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If you have an M it won't make a difference - the steering on the M is hydraulic.

What top mounts are you running on the front?

What tyre brand and type are you running? (and are they run flat?)

I'll be honest, unless I've missed something (I have only really skim read the thread) - your symptoms just sound fairly typical of chucking a load of harder suspension components at a road car, possibly combined with old tyres which have worn to a different geo. There's now no give or flex in any of the suspension components over road imperfections, and no doubt with the kw coilovers set on hard, when the road changes camber it now directly affects the steering. This is all exacerbated by the stiffness of the coupe chassis...
 
I have a plain Coupe (just Z4M geometry).
Mehle front top mounts (done about 10k miles).
Avon ZZ5 on the front still got a lot of life. Uniroyals on the back these are new.
This is a fairly recent problem (I know what you mean about the KW's etc. but they've been on there a while).
 
Newbers said:
I have a plain Coupe (just Z4M geometry).
Mehle front top mounts (done about 10k miles).
Avon ZZ5 on the front still got a lot of life. Uniroyals on the back these are new.
This is a fairly recent problem (I know what you mean about the KW's etc. but they've been on there a while).
Click to expand...

Why oh why haven’t you normalised the situation by running a matched set of tyres that are sized for the car as part of your checks...there have been many many cases of poor handling caused by mixed tyre profiles/manufacturers/types even within manufacturers?

Whereas many people have not had any apparent issues with mixing tyres if you have an issue this would be a logical point to start..

I could go on about a myriad of possible effects from wear rates / mixing tyres etc but seems like a logical place to start ?
 
I do hear what you're saying (the tramlining nearly killed me - literally). That said in the last 10 years and 70k miles I've lived with a lot of tyre combos and this really is different. I've been through, broken springs, knackered shocks, every bush etc. I'm convinced this is something different. I've spent about £2,000 on it this summer with nothing fancy to show (and still no working aircon!) so I'd really like to narrow it down and explore the options before I replace two more tyres that have less than 10k miles on them.
I'm really close to chopping it in for something else but couldn't even sell it like this :cry:
 
Changing two tyres is probably the cheapest thing to try next. You could always sell the two that come off or keep them as spares
 
Re-reading all your attempts to correct the faults I fully sympathise...

The issue as a bystander is that you have twiddled with so many things you have lost any reference...

One straw to grasp is the EPS , have you checked it for full functionality, some of your symptoms sounds like power steering failure / wear?

My only suggestions are to rebase the car by putting tracking back to standard not z4m and normalise the tyres..then see what gives...

In the past I ruined the handling of one of my bikes by having the rear shocks setup completely wrong..
 
Really intrigued by this now. Again, I can’t help but draw similarities between your description of the steering behaviour and how my si felt with knackered lollipop bushes. But if you now suspect the EPAS, does that mean that the sensation of the rear axle steering the car has gone away? Or are you actually going a bit loopy? I probably would be! :roll:

The other thing I keep going back to are the changes you made just before noticing the handling issues. Tyres and lowering. I came across this description of “tire pull”, which is a long shot but something I hadn’t heard of before. You could rotate rear tyres to see if the behaviour changes (although I note you said the left/right behaviour is the same).
 
Have you driven a "normal" Z4 back to back?

Easy to over-analyse these things if your not careful. Every time I bleed brakes in any car I'm always convinced there's air in there and it's gone spongey - but I'm just looking for it!
 
Just seeing this - had similar experience as if the rear end was acting like a pendulum... scary when you’re expecting it to dig in.

I went not only Poly RE RTAB’s but also RE RTAL’s, new drop links, Michelin PS4s’ and a B12 billy kit.... oh & a E46 CSL alignment

It now scares me how much she’ll grip before she starts to go & even then she doesn’t suddenly snap like she used to...

Interested to know how u get ion
 
All good points! I haven't changed one thing at a time and I never got it properly dialed in after it was lowered which makes it tricky to diagnose. The other thing that is a real pain I seem to struggle to get out when there's no traffic which makes it really hard to repeat the symptoms and accurately define them. I'm fairly comfortable that deep down the car is basically pretty well balanced now - better than it has been since it was lowered. We've been through a lot together often at a significant pace so this is a car I know very well. I also had an E46 for over 10 years before it so I know all about the tyre issues. I've previously never found the rear to be very sensitive (even with tired Bridgestone Potenza's - I could live with them till they were on the limit) the real problem was the front. At the moment I wouldn't want my wife (or anyone else that's not ready for it) to take it on a fast road.

MrPT
I came across this description of “tire pull”
Click to expand...
Interesting. I guess if you extrapolate this then tyres warn unevenly (even if the same on both sides of the axle) would definitely cause problems but I just don't believe that's the main issue.

The feeling of all the weird behaviour being specifically in the rear is much less pronounced now. This improvement would seem to have been a combination of upper wishbone bushes and damping. I suspect the biggest factor was a difference in the damping left to right (not sure how that changed :? ). It is a pretty hard ride which is not nice for hours on the motorway but I could live with that if it didn't scare the sh*t out of me! To Jembo's point - I'd check your shock absorbers.

The only things that are not new are the subframe bushes, the engine mounts and the inner ball joints on the steering rack but it's just been MOT'd, specifically inspected by BMW (when they were in the doghouse) and I've looked as closely as I can. It's all in pretty good condition so I really don't think the problem is there.

It's quite possible that there are a combination of issues (e.g. tyres might help a bit) however, to take one thing that I clearly experienced several times. I definitely noted on several long motorway bends where I stayed in the middle of the lane (so little if any moving over the ruts) the same sensation. It was like being pushed sideways, then it stopped, then it happened again - three times which was when the road straightened out each time. Like I said a bit like driving too fast in a high sided van that doesn't have a lot of weight in it. However I'm becoming increasingly sure this is related to the power steering. It was too regular and firm to be anything alignment related (e.g. toe-in) or slack (in a worn bush). After all the suspension was loaded up and there was no mid-bend steering input so really the car should have been stable at this point. Whether this is related to the fidgeting in a straight line is another matter.

So I think I need to explore the power steering and possibly (although there are no lights) the DSC. It will probably be tricky to find a piece of road where i can recreate the problem and see if anything is different after pulling the fuse out but I think that's the next step.

I keep telling myself that if I buy a 911 or even a Panamera it would be no guarantee that there wouldn't be problems.....
 
Have you only just switched to z4m geo? Again this is another change from previous which is not going to help diagnose the issue.

My advice would be to do the following -

1. Revert to previous geo settings which were known to be good - and get the garage that did that setup to do it again to remove any potential setup error between different garages/equipment.
2. Check if you have set the ride height correctly on the coilovers (very easy to get one slightly out and pre-load the arb one way or the other)
3. Change the tyres so all four are new and non-rft.

Epas issues shouldn't manifest as feedback from the steering - Epas effectively removes feedback, so unless the wormdrive is a little loose (which would present as looseness in the steering) its unlikely to be causing your issues?
 
Some tales from my corner: I bought my Zed in May last year and was alarmed by its handling on my drive home. The bump steer was so bad that I very nearly lost it on a couple of occasions, while its inability to hold a line at any point in time meant I was exhausted when I got home after the 50 mile drive on back roads. It's fine now (as fine as an EPS E85 Z4 can be, anyway!), after quickly sorting the following:

1. Damper lockout collars had been fitted to the NSF damper, taking away all suspension travel on that corner. Removed these - bump steer no longer chronic. Not a problem in your case, but part of my story!

2. Fiddled with EPS eccentric ring before I understood it, made things worse.

3. Replaced lollipops up front. One of the old ones was in bits. Decent improvement in feel.

4. Swapped wheels front to rear. Enormous improvement, car would now run straight. Front tyres had been in good condition, but the car simply didn't like them. Completely different tyres front to rear, but it ran straight with them mismatched. The front axle just preferred my rear tyres. Have since fitted Eagle F1s up front only and it's still happy.

5. Adjusting the EPS eccentric ring again. This was the final step for me to getting mine to be pretty much as good as an E85 with EPS can be, in my opinion. I've described sticky steering in lots of other threads, but generally speaking, the resistance through the wheel changes markedly as ambient temperatures pick up if you have sticky steering. If yours is the other way, and is loose, then turning on the sport button should improve the feel a little. The EPS does numb the feedback through the wheel, but turning on the sport button should take out perceived free play in the wheel.

If your travels ever take you to Somerset, please let me know and bring the car to me. To adjust the eccentric ring takes under an hour, and I've developed a good feel for it now, having dialled out a few forum cars and my own. Just drop me a message if you're ever heading this way.
 
Newbers said:
All good points! I haven't changed one thing at a time and I never got it properly dialed in after it was lowered which makes it tricky to diagnose. The other thing that is a real pain I seem to struggle to get out when there's no traffic which makes it really hard to repeat the symptoms and accurately define them. I'm fairly comfortable that deep down the car is basically pretty well balanced now - better than it has been since it was lowered. We've been through a lot together often at a significant pace so this is a car I know very well. I also had an E46 for over 10 years before it so I know all about the tyre issues. I've previously never found the rear to be very sensitive (even with tired Bridgestone Potenza's - I could live with them till they were on the limit) the real problem was the front. At the moment I wouldn't want my wife (or anyone else that's not ready for it) to take it on a fast road.

MrPT
I came across this description of “tire pull”
Click to expand...
Interesting. I guess if you extrapolate this then tyres warn unevenly (even if the same on both sides of the axle) would definitely cause problems but I just don't believe that's the main issue.



So I think I need to explore the power steering and possibly (although there are no lights) the DSC. It will probably be tricky to find a piece of road where i can recreate the problem and see if anything is different after pulling the fuse out but I think that's the next step.
Click to expand...



I have a very similar problem. What I can explain is that at around 60-75 mph, the front goes lighter and the steering wanders. It feels like the car is light at the front due to wind etc.... that’s the only analogy I can come up with . It only does it around 60-75 mph going in a straight line... corners etc, no problem. There’s nothing wrong with any of the bushes etc as I’ve had it all checked, brand new tyres all round, poly bushed...

New 4 wheel Hunter alignment, the lot

I’ve tried different tyre pressures, and still does it. :headbang:

The only thing that I haven’t tried is a steering angle reset... I wonder if that may fix it?

Or the concentric ring is maybe backed off too much, as I’ve never had sticky steering.

:?
 
Quick update...
I took the fuse for the power steering out. There are actually three referenced, I just took out one. I managed a bit of town, country lane, dual carriageway and motorway but unfortunately heavy traffic so barely made it to the speed limit on any of the roads. I was taken by how little steering input I naturally make when I drive so I made a point of actively going round corners rather than straight through them as normal. Also it was really cold because the fuse apparently also protects the heater fan!
What did I learn?

  • As you'd expect the steering is really heavy when you're moving slowly. It would be dangerous if you're not really paying attention and planning ahead.
    A couple of times I got the slightest bit of weirdness (driving straight when it was a bit bumpy) but I can put this down to the tyre mismatch. I didn't experience anything that I described above.
    Generally I was relaxed and not constantly correcting (or on edge wondering if at any moment I was going to have to correct). That said I didn't get to go far over 60MPH.
    There is some quite pronounced notchiness when turning the wheel for a sharp turn (e.g. roundabout). I'm wondering if this is normal as I was having to turn the motor but perhaps it indicates something is worn or needs lubricating.

I'm feeling slightly reassured about my mental health - specifically that my perception was that the problems were less pronounced with the Sport button on.

What next? I'll:

  • put the fuse back in!
    jack up both front wheels and manually turn the wheel to see what I can feel.
    check the UJ's (I hear they can need lubricating)
    investigate re-calibrating the steering sensor (I can understand how this might impact straight ahead behaviour but not the pulsing in the bends)
    investigate more the sticky steering EPS eccentric ring issue as wonkydonky's experience above
    see if anyone has any more suggestions!

Ed Doe
What top mounts are you running on the front?
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What were you thinking? That they might be knackered and loose or binding?

Wonkydonky
If your travels ever take you to Somerset, please let me know and bring the car to me.
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Very kind offer and very much appreciated! No plans to head out west for the foreseeable but definitely noted!
 
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