Time for a huge update.
Over the last year I've been chasing a huge steering issue that seems to plague these Z4's and the forums are saturated with tales of what it could be and no definitive answers. So I decided to tackle this alone and find out for myself what was causing the issue.
Just to give other zed owners some background info the Z4's, non M's all have electric steering coupled to a manual rack. The column is assisted by a huge worm gear motor inside the car. These units themselves can be temperamental. Z4's in the beginning were all being plagued with sticky steering that got worse in hotter weather almost felt like a notchy feeling in the steering. BMW luckily realised this early and changed the way they made the columns slightly. (different grease / Worm drive clearance) So this shouldn't be an issue for me owning a late 2007 coupe. It was also not the problem I was feeling in my steering. The net is full of guides on how to overcome this issue at very little expense.
So back to my problem, mine was only noticeable in a straight line. It was feeling like something was loose, I could feel play in the steering in a straight line but the wheels didn't move so it was a very bizarre feeling. My imeditae thought was maybe I have a ball joint gone in the steering somewhere so I replaced everything I could get my hands on as seen above. I went further and replaced the tie rods along with track rods.
I then had the car re aligned using the hunter equipment, I even opted for the M3 CSL settings. But the issue was still there.
Next I removed the UJ coupling between the rack and the column and found it was solid.
I held onto the end of the steering column and gave it a shake and found no movement at all. So getting slightly desperate now.
This now left me with two items to inspect. The rack itself and the EPS (electronic power steering)
First I removed the rack and got it inspected I'm no rack expert so I got another pair of eyes on it. They confirmed the rack was solid and in good health.
So now I'm left with one item, the EPS system attached to the column. Again I'm not expert with this unit but It needs to come out so I can have a look and I'm glad I did.
First I had to remove the foot well panels to gain access very quickly you can see the size of the unit all together. Square peg round hole came to mind looking at it.
Only 8 bolts (ali bolts) hold it in place plus a ton of connectors. I made sure I left the steering lock on and marked any items I removed off the spindle to keep the alignment. It quickly became clear I was going to need to split the motor from the column to get it out, this proved very difficult upside down! but I got there in the end after a lot of swearing.
First observations were good. The bearings at each end looked solid and well packed with grease. The worm gear on the motor looked well coated aswell, prodded and poked the assembly for half hour looking over its construction then I found the issue.
It was do with how the motor engages on the column, I observed when removing the motor that there was an adjustment ring between it and the column body which can rotate, Once I took it off and had a look it became clear it controlled how much the worm gear engaged the column. When I removed It, it was in the slackest position (See photo)
In this position I could create play in the column replicating the feeling I was getting in the steering, the more I move the ring anti clockwise the less it would allow me to move the column removing the backlash.
Amazing! It's taken me ages to get to this point. But one thing I need to bare in mind is this road could lead to the original problem that plagued the early z4's. If you fully engage the worm gear the motor has to work very hard causing a lot of heat. So now I need to find a happy medium that takes up the play and wont cause too much friction.
So this is where I am at the moment, I called it a night at about 8pm last night I don't usually play on school nights but the curiosity got the better of me. Timing wise it's not been too bad, it took me 2 hours last night to remove the column and get to that point it also took me and hour the night before removing the rack, that was very simple. Again this is all easily doable in your own garage.
The interior looks odd with no column and wheel
Tonight I will reassemble everything, currently the rack is still on the floor and the column is on the bench ready to go. Watch this space.
