When BMW built the E85 they based it on the series 3 for the running gear. For some reason known only to themselves they did not use the same steering system but instead used the EPS which has caused no end of problems and was even the subject of a recall. Thankfully parts from the E46 series will fit.
The two racks compared. Pinions are very different.The first part you will need is the E46 power steering rack with a purple tag. The purple tag refers to the badge on the rack which is purple in colour instead of silver. It has exactly the same turn to turn rate of 2.9 as the Z4. I bought a reconditioned one and some new tie rod ends total cost £200. If you are doing it this way this you will need to scavenge the tie rod nuts and cups from your old rack. The only thing wrong with the rack is that the pinion is smaller than the one on the Z4. The Z4 intermediate shaft will just not fit as it is too big. You will need the shaft from a Z4M which you can buy new from BMW for around £250. Ouch! With this shaft both couplings are the same size. What you could do is to get another Z4 shaft and get an engineering firm to swap the steering column pinion for the smaller shaft so that you will have one shaft with the couplings the same size. In a previous post concerning this the owner had merely removed the plastic guide cover and tightened up the joint to fit. I would strongly disagree . Either get the Z4M shaft or get the Z4 altered. v8z8 had a special one made up by a specialist.
the two shafts upper is the Z4M
the two shafts showing the difference in size. For the first stage safely jack the car up and fix the steering straight ahead. Remove the key and lock the wheel. The wheel must not turn otherwise damage to the clock springs may occur. Remove the plastic undertray then the metal undertray. The rear four bolts point at an angle.Remove wheels. Remove tie rod ends. One came away easily while the other needed a bit of heat. Disconnect the intermediate shaft at the baulkhead, no need to remove the lower one , undo the two nuts and bolts holding the rack in place and simply remove the rack and shaft down.
Rack removed. Skid pan not removed but you need to remove it You now need to assemble the new rack. As a rough guide the tie rod ends fitted onto the rack with about 20 turns. You can use the ones from your old rack but I would prefer you use new ones. You will need the tie rod nuts and caps as these were not supplied. You will need the black plastic cap on top of the pinion as the Z4 does not fit. The cap has a guide hole for the torq bolt so you know when the joint is engaged properly
You also need two torq bolts from BMW for the intermediate which are only £1 each. They have a blue coating to act as a lock and are single use only. Assemble the rack and get the rack into the neutral or straight ahead position. Offer it into place. A tight squeeze with the extra pipes on the rack but it does fit. Bolt into place. Now from inside the engine offer the shaft onto the upper steering pinion. It will only go one in one posion as there is a tab on the pinion. Don't push it fully home. from underneath line up the plastic cover to fit over the lower joint then once happy push it into position. As the shaft is sliding you can use this to place the joint so it lines up. Fit the old torq bolt not the new one. Now push home the upper joint and again use the old bolt. With the tie rods in place the whole thing should line up. Test from lock to lock. Once you are happy remove old bolts and torque new bolts into place. Mark the position of the bolts in yellow paint
new torq bolts note the blue filmTorque all remaining bolts. The first stage is now complete.
