Changing the E39 M5 Front Suspension from stock to coil-over:
The front is relatively simple to change over to coil-overs. What makes it simple is that you don’t have to disassemble the actual strut assemblies; you simply remove the factory ones and install the new ones. That said, its heavy work and you should expect to spend about an hour per side. It will take longer if you’ve never done it before.
Put masking tape on the fender lip where the damper will come through, and fold a piece of cardboard over on top of it and tape it in place. You’ll be glad you did!
The logic of the job is pretty simple:
Start with driver’s side (left, looking forward). Jack up the front corner or both sides at the front. You’ll need to have a floor jack free while you work so if you have two jacks that’s easy; if you only have one, then put the front end on stands so you can use the jack. For reference, the “steering knuckle” is the aluminum casting at the bottom of the strut with the wheel bearing, the brakes, the various suspension and steering ball joints attached to it. The bottom of the damper goes through a machined hole in it (the “pinch tube”) and the pinch bolt clamps it in place.
- Undo the sway bar link at the swaybar. You need a thin open end wrench 16mm (I got one at a bike store) and a 16mm socket. This allows the suspension to droop down once it’s disconnected.
- Undo the pinch bolt and remove it. This creates slack in the sensor wires and it releases tension on the bottom of the damper so it can be removed.
- Undo the three nuts at the top of the strut assembly (under the hood) and push the top of the strut assembly down and to the side to make room for the spring compressor.
- Attach your spring compressor with the draw-down screw head at the top, up inside the wheel well. If you put it on the other way, with the screw at the bottom, the top of the strut will come down but the long end of compressor bolt will prevent you from moving the strut out of the tower.
- Put a socket on a universal and a long extension down through the opening in the fender and compress the strut spring an inch or two
- Once it’s compressed enough, push the top of the strut down and rotate it out of the wheel well. Remember the cardboard covering? Now you know why. Be careful not to stress the sensor wires or the brake hose. If the brake line pulls too tight, turn the steering wheel a bit (left turn) to move the brake caliper inward and relieve it.
- With the strut outside the wheel well, use a long pry bar and lever up on the bottom of the damper to start it moving up and out of the pinch tube in the steering knuckle. Keep pulling on the tube – both of mine just slid out once they had started moving up.
You now have the old OEM unit out, and the hard part of the job is over. To get ready to install the new unit, wind its lower spring perch down so it’s near the bottom of its travel range. This will allow you to shorten the damper by pushing on it (no spring compressor needed) so you can swing it in under the wheel well.
- Clean out the pinch tube in the knuckle with a clean rag. Slip the new damper into the tube as far as it will go. If it doesn’t bottom, don’t worry. That’s where the floor jack comes in.
- Compress the damper by hand and swing the strut top back under the wheelwell
- Use the jack (padded with a block of wood) to lift on the bottom of the brake rotor and lift the top of the strut into place. Install and torque the three nuts to 18 ft-lbs.
- Lower the jack a bit, then wind the lower spring perch up until the spring is held between the lower and upper perches so that when you lift on the rotor again, the spring will keep the bottom of the strut pushed down and the knuckle can slide up to fully seat the damper in the pinch tube. Continue lifting on the brake rotor with the jack to push the steering knuckle up to seat the new damper in the pinch tube. Once it’s as high as it can go, stop lifting.
- Install and torque the pinch bolt.
- Remove the jack and set the lower spring perch up to the top of its travel. This will ensure nothing bad happens when you put the car back on the ground.
Switch your tools and get ready to do the passenger’s side (right, looking forward). At this point, the driver’s side is complete except for re-connecting the sway-bar link. You’ll go back and do that after you finish the other side.
The second side is the same as the first except that you have to undo the headlight sensor link so it doesn’t get broken when the suspension droops. Once again:
- Undo the headlight sensor and the swaybar link at the swaybar
- Undo the pinch bolt , undo the top of the strut assembly, compress the spring and rotate the top of the strut out of the wheelwell and remove the damper from the pinch tube .
- Install the new strut assembly, and repeat the process of assembling it into the strut tower and the steering knuckle.
- Install and torque the pinch bolt.
- Set the lower spring seat as high as it will go
- Re-attach the headlight sensor rod and the swaybar link. Return to the first side and attach its swaybar link.
Put wheels on, put it on the ground, and check the ride height. You’re done.
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