Replacing the strut inserts on my 1992

    • Offizieller Beitrag

    Some time ago I offered to write down some instructions for replacing the strut inserts on my 1992 non-EDC 850i, 6-speed. This was precipitated by a badly leaking left oem Boge strut and a pair of torn upper control arm bushings. A series of images would help immensely, but for now..


    Tools needed:


    1. Standard half inch metric combination wrenches, socket set, and torque wrench.


    2. Metric hex Allen sockets to remove the ABS sensor (5 mm), the brake disk retaining nut (5 mm), and to hold the shock absorber piston shaft (6 mm).


    3. 22 mm goose neck box wrench to remove the Nyloc nut on the top of the strut assembly.


    4. Spring compressor


    5. Dremel for cutting off the collar nut (if necessary).


    6. Make sure that Bilstein provides the special wrench with two cogs (like an old bicycle hub tool) for removing and installing the collar nut.


    7. A thread file (SnapOn #TFM7530B) if you need to rehabilitate the threads on the strut tube.


    8. Loctite, Wurth CU 800 anti seize, and assorted chemicals.


    Procedure:


    1. Raise and support the front of the car.


    2. Loosen (only a single turn) the 22 mm nut on the top of the shock absorber piston before removing the strut assembly from the car. This nut is under the plastic cap at the top of the shock tower. It is much easier to hold the shaft (6 mm Allen hex) in place and break loose the 22 mm Nylon nut in situ. You will need a 22 mm gooseneck for the nut. I put a breaker bar on the hex socket and held that in place while I turned the gooseneck. While you are at it loosen the three nearby 13 mm flanged retaining nuts that hold the strut bearing assembly to the shock tower.


    3. Remove the wheels. Under the car remove the bottom 17 mm nut on the sway bar link. Use a 5/8" open end wrench (I didn’t have a 16 mm) on the inner flats to keep the ball from turning. Next, loosen the three large bolts on the bottom of the steering arm that hold it to the strut assembly. You will need to use Loctite Blue on these three when it comes time to reassemble.


    4. Remove the two 19 mm caliper carrier bolts, pull the caliper away from the brake disk and support it up under the wheel well so that there is no stress on the brake line. Then remove the 5 mm hex screw that holds the brake disk in place. If the hex screw is corroded (you forgot to use an anti-seize last brake job), use either an impact hammer or drill it out. Set aside the brake disk.


    5. Detach electrical connections: i) the brake wear sensor on left side has a connector just behind the top of the backing plate, and ii) the ABS/ASC sensors on both sides. Remove the 5 mm Allen hex screw and pull out the ABS/ASC sensor from the lower spindle assembly. Unclip the cable shroud from its bracket on the strut and let the wires hang free.


    6. Remove the three steering arm bolts that you loosened in #3 and separate the arm from the strut assembly. There is a slot between the two parts and it may be necessary to pry them apart using a large screw driver. At this point the steering arm will drop out of the way with three parts still connected to it: i) the lower control arm (aluminum $$$), ii) the upper control or thrust arm, and iii) the tie rod. Check the condition of each to see if any of them, particularly the upper control arm bushing, need to be replaced. Replace any other worn suspension/steering parts (tie rod ends, idler arm, track rod or bushings).


    7. You are now ready to remove the strut. Remove two of the 13 mm flanged nuts that you loosened in #2 above and while holding the spring with one hand remove the third and last nut. Voila, the entire assembly swings out of the wheel well and onto a waiting pad. Go have a beer.


    8. On your bench use the spring compressor to take the pressure off the top bearing. Follow the compressor instructions carefully for spacing and safety. Span as many coils (~4) as you can.


    9. When the pressure is off the bearing, remove the top Nyloc nut you loosened in #1 and remove the stopper, bearing, support, bump stop, rubber boot, upper and lower spring pads and spring.


    10. Inspect the collar nut on the top of the strut. It is likely quite rusty and if it is like mine, nearly impossible to remove... enter the Dremel. I carefully cut away the collar nut with four vertical cuts, and needed an additional half day cleaning the threads with a thread file (1.50 mm pitch) and repainting the few rusted parts of the strut. Be careful if you need to use the Dremel, do not cut into the strut tube. After removing the collar nut, the insert assembly came out with a little encouragement. Careful, there is a special oil that will get all over you when you remove the insert. Fluid had leaked out past the strut seals because both the collar nut and the top 1/8" of the inside of the strut tube had rusted. There is no inner tube, just a piston and series of seals.


    11. Clean everything, particularly the lower strut perch (including the drain hole), the backing plate (check for cracks), and the threads for the new collar nut. The new collar nut supplied by Bilstein is brass/plated and should not rust.


    12. The bearing at the top of the strut piston located way up in the shock tower is designed in such a way that it catches a lot of dirt in a circular moat. There are four small drain holes and over time they clog up. Repeated flushing resulted in the bearing working smoothly again. It cannot be disassembled or lubricated.


    13. I purchased the Bilstein Sport inserts for under $200 each (MSP-05491 front/MSP-05490 rear). No bump stops were provided and none were needed as there is an internal bump stop in the Bilstein front shocks.


    Reassembly:


    1. While at it I removed the upper control arm and pressed in new bushings (provided by Paul from Downunder). This is a lot easier to do with the strut assembly on the bench and out of the way.


    2. Use the Wurth cu800 anti-seize on the strut tube’s threads (and elsewhere) but
    not where you use either a Nyloc nut or Loctite.


    3. Assemble in reverse order.


    4. The total piston throw of the Bilstein replacement insert appears to be shorter than the Boge oem unit, so you may need to compress the spring a bit further to get the parts back together. Work slowly.


    5. When you tighten the tie rod ends to the steering arm the screw may turn when the nylon insert comes into contact with the threads. An old trick is to use a regular nut to tighten the shank down and then simply replace this nut with the new Nyloc nut.


    6. Make sure the flats on the sway bar links are perpendicular to the sway bar itself. That maximizes the surface area subject to torqueing when cornering.


    7. Torque everything to specifications and get a front end realignment.


    8. Drive away with a tight front end.


    Overall impressions are that the front end is clearly tighter, quieter and less “skittish.” Beware, this is only a job for those who are willing to take the plunge into serious repair work, and these instructions may be of little use to someone with an EDC version e31.


    Addendum: On February 1, 2003 “Allan” posted a brief description on RoadFly for replacing the oem Boge inserts with Bilstein shocks for a 1992 850i equipped with EDC titled “EDC Strut Removal”. His conclusion was that Bilstein Sport Shocks fit the EDC tubes and that a pair of 1 3/8" freeze plugs seal off the holes left by the removed EDC control plugs.


    Torque Values:
    1. Brake caliper bolts (2) 19 mm 81/91 ft lb 110/123 Nm
    2. Steering arm to strut (3) 19 mm 48 65
    3. Upper mount (3) 13 mm 16 22
    4. Lug bolts (5) 17 mm 85 110
    5. Strut top bearing nut (1) 22 mm 48 65
    6. Strut collar nut 96 130
    7. Upper control arm ball joint end 63 85
    8. Upper control arm thru bolt 22 mm 96 130

    9. Lower control arm ball joint end 77.5
    10. Wheel bearing nut 36 mm 215 290
    11. Sway bar link 17 mm 44 59
    12. Tie rod end 33-40


    Jon Nelson: 9/24/2002

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