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  • Front Strut Replacement The Hack Mechanic Way

    Front Strut Replacement The Hack Mechanic Way

    Front Strut Replacement



    Okay. It's time to replace your front struts. Maybe you're doing it as part of a shocks-and-struts job. Maybe you're updating the entire suspension—shocks and struts, springs, and sway bars. Maybe you're doing a full front end refresh including ball joints, tie rods, center track link, and idler bushings. Maybe you're doing an undercarriage refresh and are sandblasting and repainting the subframe and strut housings at the same time.


    Whatever the reason, if you've never done this before, there are a few things to know. Rear shocks are trivial—jack up the back of the car, pull the wheels off, undo the 19mm nut at the bottom, bang the shock off the slanted stud with a rubber mallet, undo the two 14mm nuts at the top, drop out the old shock, pop in the new shock, done—but front struts aren't. If no other related parts are bad, you can easily get both struts done in an afternoon. But the strut directly or indirectly touches many other components, so it's easy to slide down the slippery slope. If you want to, that's fine. And sometimes, when you get partway into it and find that other parts are bad, you have no choice. But you also can stay on task, get 'er done, and enjoy the fruits of your labors.



    • New strut cartridges
    • New strut tower bushings ("hats") if they're bad
    • New upper and lower perch rubber if they're bad



    • Spring compressor
    • Two big pipe wrenches
    • 13mm socket and wrench 
    • 14mm socket and wrench
    • 19mm socket
    • Rubber mallet, hammer, and chisel
    • Wire cutters and needle-nose Vise Grips
    • Possibly a MAPP gas torch


    The Big Picture

    When we say "front struts," we're talking about the replaceable front strut cartridge that threads into the tube that's part of the strut assembly. But the larger context is that this is a Macpherson strut assembly, which is a type of front suspension where the springs and shock absorbers are mounted along the steering axes. That is, when you turn the steering wheel, it actually rotates the springs and shock absorbers (struts), which in turn moves the front wheels and tires tire. Note that the other major sportscar front suspension is a double-wishbone or double-A-arm, where the springs and shocks are not attached to the wheels and have no role whatsoever in the steering.


    The left front strut assembly. You can see how it not only suspends the car and absorbs shock, but also turns the wheel.

    It's helpful to understand that BMW used two primary MacPherson strut designs. On the 2002 and up through, I believe, the E30, the design had the strut housing (the tube) and the spindle (the stub axle that the wheel bearing, hub, and rotor spin on) as a single lifetime-of-the-car unit. The strut cartridge was the replaceable part that threaded into the top of the tube. The steering knuckle to which the ball joint is attached bolts to the bottom of the strut assembly. In contrast, beginning I believe with the E36, this changed to a different design—the strut cartridge and the housing became a single replaceable unit, and instead of the spindle being a permanent part of the housing, the spindle was integrated into steering knuckle, and this lifetime-of-the-car component bolted to the bottom of the housing. None of this changes anything with regard to doing the struts on a 2002, but it will help you if you're daily driver is, say, an E46, you order front struts for it, they arrive, you open up the box and think "what the hell am I looking at?"


    The strut cartridge being slid out of the tube in the strut assembly. This is actually off my 635CSi, but the configuration on a 2002 is similar.


    e46 bilstein struts.jpg
    Stock photo of a set of Bilstein front struts for an E46, showing how the replaceable part is no longer a "cartridge" but is instead a structural housing as well.


    Back to the 2002 struts. The lower spring perch is an integral part of the top of the strut assembly. The spring sits on top of it. On top of the spring is the upper perch, which is a plate with a hole in the middle. A piece of perch rubber sits between the spring at the perch at both the top and bottom. The strut cartridge has a piston that extends upward through the hole in the middle of the upper spring perch. On top of the upper perch is a small spacer (really, a washer), and the strut tower bushing/bearing (sometimes called "the hat") sits on top of that, with the threaded tip of the strut cartridge's piston sticking up through the bearing in the center. A washer, a cylindrical spacer, and another washer slide over the top of the piston, and a Nyloc nut threads into the tip, holding it all in place. I'll get lazy for a moment and just pilfer one of c.d.iesel's illustrations that can be found here on the FAQ, as all of the components are plainly visible in it.


    c.d.iesel, we miss you..


    To be clear, when I refer to the "strut housing" or the "strut tube," I'm referring to the major life-of-the-car component consisting of the tube, the lower perch, and the spindle. When I refer to the "strut assembly," I'm referring to the entire assembled unit with the strut cartridge, spring, hat, hub, and rotor all installed.


    This is what I'm referring to as the strut assembly.


    But here's the thing: The spring is under compression. It's being squeezed by the "hat" that's held on by the Nyloc nut that's threaded onto the piston extending from the strut cartridge through the middle of the hat. So if you undo that nut, as soon as its threads no longer engage those on the tip of the piston, the compressed spring will un-compress and launch the hat and the spacers, possibly right into your face. This is extremely dangerous. Because of this, you never, ever, under any circumstances should undo that nut without first compressing the spring. Got it? Good.


    (Having said that, I should also walk it back just slightly. If the car has lowering springs and gas shocks, once the strut assembly is removed from the car, the combination of there no longer being weight on the spring from the car, and the gas shock extending and thus pushing the hat up as far as it'll go, can make it so there's not any tension on the spring. But with stock springs, this is never the case.)


    So, to replace front strut cartridges, the big picture is that you have to first:

    1. Remove the strut assembly from the car and lay it on the floor.
    2. Use a spring compressor to compress the spring to take the tension off the hat.
    3. Remove the hat.
    4. Remove the spring.


    Then and only then you can remove the cartridge from the tube of the strut housing.


    Now, it is sometimes possible to do this without completely removing the strut assembly from the car—and I'll get to that—but it risks damage to the paint on the fender lap, and it doesn't always work.


    The Spring Compressor

    You'll read two extremes online regarding using a spring compressor. One extreme is that some people are too cheap to buy or rent a real spring compressor and instead will use hose clamps or even zip ties. I, in my persona as The Hack Mechanic, will certainly scrounge my way around not having every special tool, but this is absolute idiocy. Any AutoZone, O'Reilly's, or Advance Auto Parts will rent you a spring compressor at zero cost (buy it and return it for a full refund). The simplest "claw"-style compressor is less than twenty bucks on Amazon. Why anyone would go to all the extra work, much less accept the inherent safety risk, of something like hose clamps and zip ties when using something purpose-built is either free or costs less than a pizza is beyond me. (Note that, for the springs on my Lotus Europa, I did have to build my own spring compressor with hooks and turnbuckles because there is no commercially-available compressor for springs that small and whose coils are that tightly stacked—not even a motorcycle spring compressor would work—and when I asked a Lotus parts supplier what they used, he described something home-built and virtually identical to mine. But I digress.)


    But the other extreme is where people caterwaul that using a spring compressor is an inherently dangerous activity where one false move will kill you, and thus you're crazy to even attempt replacing front struts yourself and are better off leaving strut replacement to a professional. This is a massive overreaction. Use the spring compressor as it's intended, don't use a $20 compressor meant for a little itty bitty spring on a Toyota Yaris to compress massive springs on an F350, pay attention every step of the way, and as an added safeguard, just in case something happens, don't ever aim the compressed spring at your head. That's really about it.


    If you look on Amazon or eBay, you'll see four main types of spring compressors:


    1) The Claw: The simplest and cheapest. These are a pair of threaded rods, each of which has two opposite-facing two-pronged claws. One claw is fixed at the end of the rod. The other moves up and down as you tighten or loosen its nut. You put the pair of them at 6:00 and 12:00 on the spring and tighten their nuts round-robin to compress the spring. The main advantages of The Claw are low price and light weight. The main disadvantage is that it doesn't compress the spring evenly. At best, you need to alternate tightening one, then the other, to keep the both sides of the spring evenly compressed. At worst, it's possible for one of them to "walk" along the spring until it slides down next to the other one, creating a huge bulge-out on one side of the spring. Some but not all claw compressors have safety dowel pins to prevent the spring from accidentally slipping out from under the claw.


    claw compressor.jpg
    Your typical eBay $20 claw-style compressor. This one has no safety dowel pins.
    claw with pins.jpg
    A $32 eBay claw compressor with safety dowel pins.

    2) The Clamshell: This design looks a bit like Pac-Man or like an A-frame house on its side. It uses a threaded rod to pull together two assemblies that are hinged at one end.  Hooks and metal pins are used to secure the spring. I believe that the original tool is from the respected tool house OTC, and is not cheap; Amazon sells them for almost $350. As is often the case, Chinese-made knockoffs appeared a few years back. A quick look shows that those appear to be largely gone from eBay. I can't say that I've ever used the clamshell, as it never appeared to be terribly substantial to me or to have a great amount of range.

    otc clamshell.jpg
    OTC clamshell compressor.


    3) Plate or Fork-Style Compressors: In 1984, I bought the spring compressor that BMW CCA co-founder Michel Potheau at the legendary Circle Tire Corporation (CTC) sold in the centerfold ad he had for years in Roundel magazine. I still have it. It looks like a 2002 tire jack onto which someone has welded a pair of angled or slightly twisted plates that slide between the coils of a spring. You then turn the crank, and a threaded rod in the backbone of the "jack" raises the lower plate, thus compressing the spring.


    My ancient battle axe of a compressor, purchased from the hand of Michel Potheau himself. You can see the angled twist in the plates to allow them to slide between the angled coils of the spring. The little tabs on the end help ensure that the spring won't slide out.

    This is an example of what I call a plate compressor, but apparently they're referred to commercially as fork compressors. A variety of them, mostly Chinese-made, are now available on eBay and Amazon for $120 and under. But instead of having a hand-turned crank, they have the head of a bolt at the bottom of the backbone that can be turned with a wrench or a socket (or, if you want to shorten its life, an impact wrench). And they generally come with two or three different-sized plates to accommodate springs of different diameters. The huge advantage of these is that, unlike the claw or the clamshell that only contacts the spring at two points, the plate makes contact with the spring essentially all the way around, virtually eliminating the chance of slippage. There's another advantage that I'll get to when I discuss the alternate removal method. The disadvantages are cost and weight. I give a strong recommendation to this style of compressors.

    My recently-purchased plate-style compressor comes with three different sized plates.
    The assembled plate compressor.

    4) Upright compressors: Commercial shops have long used heavy duty upright spring compressors. Some bolt to a wall. Others are free-standing. Some simply have a long lever arm that you pull to compress the spring. Others have a drill-press-like three-armed spindle wheel and gearing for mechanical advantage. A third type has an integrated bottle jack, letting a rising hydraulic cylinder do the work for you. As with so many tools, what was once only available to pros has been copied and stamped out. The main advantage is that they hold the strut assembly securely and compress the spring quickly. The main disadvantage is size and cost. I've never used one.


    Of the above four types, I strongly recommend the plate or fork-style compressor. But, again, even a rented set of claws or one purchased on eBay for $17 is going to be so much better and safer than hose clamps. Don't go there.


    The 2002 Strut Cartridge

    Grossly speaking, 2002 strut cartridges fall into three categories:

    1. Oil-filled. I don't know if all 2002s originally had oil-filled strut cartridges, but I believe all the round tail light cars did. These are "wet" cartridges. The cartridge is not the full diameter of the strut tube. When you remove the cartridges, oil streams out the bottom. And when you tip the strut assembly upside down, more oil runs out.
      An original oil-filled strut cartridge. Note how much smaller it is than the diameter of the strut housing.
    2. Hydraulic. These are oil-filled as well, but they're "dry" cartridges. They're the diameter of the strut tube. If they're leaking oil, they're bad.
    3. Gas-filled. Oil-filled struts and shocks don't really have a preferred direction. When they're out of the car, it takes about equal effort to compress or to expand them. In contrast, the natural resting state of gas-filled or gas-pressurized struts and shocks is fully extended. When they're out of the car, if you compress them, they'll immediately expand back to their extended state. The pressurization and internal valving is or should be tuned to a car's weight so that, once weight is on them, they're more or less neutral with regard to up or down motion, but all other factors being equal, a car with gas shocks such as Bilsteins may sit a little higher at rest than a car with fluid-filled shocks.
    A Bilstein strut cartridge whose diameter essentially fills the strut tube.

    In terms of removal and replacement, it doesn't really matter which type you have. They're all held in place in the tube with a collar nut that may have required a special tool back in the day, but after decades, it usually takes a pipe wrench to get it off. Just be aware that, when you undo the collar nut and start to lift the old strut cartridge out, if it's narrow instead of filling up the entire tube, it's a "wet" cartridge and it's going to dump oil all over your garage floor if you're not careful.


    The Standard Procedure


    Now that you understand what a Macpherson strut is, what portion of it in a 2002 is the standard replaceable part, and what the spring compressor does, here are the steps for the standard procedure to remove the strut assembly and replace the strut cartridge. There are a total of 11 nuts/bolts on each side—14 if you count the lug nuts.


    Removing The Strut Assembly

    • Jack up the nose of the car and set it securely on stands.
    • Work on one side at a time.
    • Remove the wheel (so, unless you have an impact wrench, crack the lug nuts before you jack up the car).
    • Use a 13mm socket and wrench to undo the bolt and nut holding the brake lines to the retaining plate on the strut assembly. 
    • Use a 19mm socket to undo both of the bolts holding the caliper to the strut assembly. They're usually pretty tight. A pipe on the end of a breaker bar makes short work out of them.
    • Pull the caliper off the rotor and out of the way. I usually just set it on the control arm.
      Caliper Removed
      The caliper removed and set on the control arm.
    • Use a 13 or 14mm socket and wrench, depending which size the car has, to remove the two nuts at the bottom of the sway bar link, and then remove the retaining plate and the rubber bushing. This isn't absolutely necessary, but it allows the control arm to dip lower, which helps you get the strut out.
      The sway bar end link locking nuts.
    • Look at the very bottom of the strut assembly where the steering knuckle is attached and identify the three 14mm bolts with little holes in their protruding heads. The one that's above the center of the control arm is easy to see, but will be hard to remove. The other two are practically against the brake backing plate.
      The bolts with their safety wire holding the steering knuckle to the bottom of the strut housing.
    • Originally there was safety wire running through the holes. It may or may not still be there, as some folks rely on Loctite instead. If the safety wire is there, use wire cutters to cut it between all three bolts, and pliers or needle nose Vise Grips to pull it out. If it's rusted in place in the holes, penetrating oil such as Silikroil may help free it.
    • Position the steering wheel so the wheels are facing straight ahead, and remove the key so the steering locks in this position.
    • Use a good six-pointed 14mm socket and a short extension (or a long socket) to remove the two bolts that are against the backing plate. You really, really don't want to break or round the corners off these bolts, so make sure the socket is square with the bolt. If it doesn't break free, don't force it by putting a pipe on the end of a breaker bar. Instead, use a scratch awl and some brake cleaner to clean off the top of the bolt hole (the bolt threads all the way through the knuckle), then spray penetrating oil like SiliKroil on it, wait a bit, and try again. If you have a MAPP gas torch, heat up the part of the steering knuckle the bolt goes through.
      Safety wire removed, one bolt partially out.
    • For the third bolt, the one that's over the control arm, there's not enough space to get a socket on it, so instead you need to use a 14mm box-end wrench. There's not even enough space for that, so what you have to do is take a small floor jack, put it under the end of the control arm, and jack it up until you've created enough clearance to access it. Be careful that, in jacking up the control arm, you don't lift the car off the jack stand on that side. Due to the fact that a wrench is generally shorter than a ratchet handle, you may have trouble getting sufficient leverage to loosen this bolt, but again, be very careful not to round the corners off the bolt head.
      Jacking up the end of the control arm to increase access to the middle bolt.
    • IMG_8222 (2).JPG
      Reaching that middle bolt with a box-end wrench.
    • If you do strip one of the bolt heads, particularly the middle one above the control arm, I've gotten out of it by disconnecting the tie rod from the steering knuckle and unbolting the lower control arm with the tension strut attached, and removing the strut assembly from the car with the knuckle and lower control arm attached. Then, with it on the ground, you can rotate the lower control arm on the ball joint and get better access to the head of the middle bolt. But it's a pain. This is why you really don't want to round off the corners on those bolt heads.
    • With all three of the steering knuckle bolts removed, separate the knuckle from the bottom of the strut housing. It's held in place with a notch and a slot. Banging on the extended portion of the knuckle—the part the tie rod attaches to—with a rubber mallet usually frees it. If that doesn't work, tap gently anywhere on the seam between the two components using a hammer and a chisel.
      The steering knuckle freed from the bottom of the strut assembly, showing the notch as well as the castellated nut for the ball joint
    • Once the knuckle is free from the bottom, the only thing holding the strut in place is the "hat" at the top, where the three studs protrude through the underside of the strut tower. Undo the three nuts on the three studs and take off their thin wavy washers so you don't lose them. If the bottom of  the strut assembly is still sitting on top of, though no longer fastened to, the steering knuckle, it should gently settle down on it, forcing it and the control arm lower, but just to be sure (you don't want the strut assembly crashing to the ground), have a hand on the strut assembly while you remove the last nut.
      Just three nuts between the strut assembly and freedom.
    • The whole assembly, with the brake rotor on it, weights about 30 pounds. It's not that difficult to maneuver around. With everything disconnected, pull the bottom of it off the steering knuckle and toward you, then guide the top of it out from under the fender, taking care that the studs on the hat don't scratch the fender lips.
    • Lay the strut assembly on the ground.
    • Pat yourself on the back.
    Yeah baby.


    Evaluate The Strut Tower Bushings

    I call them "strut tower bushings," and many in the community refer to them as "hats," but realoem.com calls them "guide supports," and many vendors label them as "strut mounts." Whatever you call them, the part number is 31-33-1-110-195. Since you're about to remove the hats, now is a good time to evaluate them. If the rubber is cracked anywhere, replace them. They should spin freely without noise or binding. There should be little to no play in the bearing. And remember what it feels like when you spin it, because if you're reusing it, when you put the strut back together, it should feel about the same, maybe a little tighter but not binding.


    If there's nothing obviously wrong with them, I don't have any qualms about reusing them, but some folks prefer prophylactic replacement.  Genuine BMW OE hats are about $140 each. There's a large range of aftermarket parts down to about $35 each; look here on the FAQ for recommendations. If you do reuse them, you might want to pick the old caked grease out with a fine pick and repack them.

    The rubber for the "hats" is oven cracked. If it is, replace them, but if it's not and the bearing spins free and smooth, it's not a sin to reuse them.

    The Headlight Spacer

    If your car still has the original aluminum spacers between the hats and the underside of the shock tower, remove them. Their sole purpose was to satisfy U.S. federal headlight height requirements. With them gone, it'll settle down the front suspension so the car doesn't show as much wheel well above the front tires. And despite the note on c.d.'s illustration, do NOT relocate it to the top of the shock tower under the hood. They look stupid there. Seriously.


    Removing The Spring

    Okay. Onto the business end of the business.

    • Lay the strut assembly on the floor.
    • Insert your spring compressor between the coils, with the upper plate or claw as close to the upper perch as possible, and the lower plate or claw as close to the lower perch as possible.
      Preparing to compress.
    • Compress the spring until you can see and feel the tension taken off the hat. If you're using something other than a plate compressor, be mindful that you're compressing the spring as evenly as possible.
    • When you're certain there's no spring tension on the hat, it's now need to loosen the 19mm Nyloc nut at the top of the strut piston. The problem is that if you simply crank down on it with a wrench or a socket, the whole piston will turn. This is a job that's made for an impact wrench, as it'll whacketa-whacketa-WHEEEEE that nut right off. If you don't have an impact wrench, you need to hold the top of the piston still. The original struts have a little square boss at the top of the piston that you can get a little wrench on. Bilsteins have a hole for an Allen key. Note that to use either of these, you can't block the top of the piston, so you can't use a socket and ratchet handle; you need to use a wrench instead. Really, go buy yourself an electric impact wrench or an air compressor and an air impact wrench. I'm serious.
    • Don't take the nut completely off until you've made absolutely certain that there's no tension on the hat. You can tell because should be able to move the hat freely. 
    • If you're certain, undo the nut, withdraw the three spacers from the top of the piston and take a photo of them in the proper order, then slide the hat off the top of the piston, and collect the bearing dust cap from underneath, and the spacer on the top of the upper spring perch. It's a good idea to then arrange all of these in the correct order on a paper towel and photograph them.
      All the spacers and washers as they came off Hampton, my 49,000-mile 2002. I don't think they'd ever been apart.
    • Slide the upper spring perch up and over the piston. The upper perch rubber will probably come off with it.
      The upper spring perch just slides off.
    • If you're going to be reassembly the strut with a new cartridge almost immediately, you can just slide the compressor and spring as a unit (with the compressor still compressing the spring) off the lower perch and set it aside somewhere safe. If doing this gives you the willies, or if you're going to use the compressor on the other side and then, say, sandblast and paint both strut housings, you can release the tension on the spring before removing it. It really doesn't matter. But I wouldn't recommend that you leave the spring compressed for days or weeks.
      Ready to remove the strut cartridge.
    • Another pat on the back is appropriate.


    Removing The Strut Cartridge

    The strut cartridge is held in the tube by a collar nut (also referred to as a gland nut) at the top. If the struts still have the original oil-filled cartridges in them, there'll be what looks like a big hex nut at the top, but it's just a false cover. Pry it off and it'll reveal the circular collar nut.

    IMG_8234 (2).JPG
    The false cover on the original collar nut.

    The original collar nuts have two holes in them intended for a special tool with two pins. The Bilstein collar nuts have two notches in them enabling use of the Bilstein 30mm ring tool, part # E4-MS09/7, with two tabs in it.

    gland nut.jpg
    The Bilstein gland nut with the notches in it.

    In either case, the common method of removing the collar nut is to use two big pipe wrenches, the ones with the thumb ring adjusters and the serrated jaws that bite into the material. Why two ? One to twist the nut, and the other to hold the body of the strut assembly still. Make no mistake, this will dig into and mar the outside of the strut tube. I don't really care about a few serrated gouge marks in places I won't ever see. If you do care, instead of using a second wrench, you can take a long piece of angle iron, drill two holes in it the same spacing as the holes on the tab on the strut housing that holes the brake lines, bolt it on, and secure it that way. Me, I put the second wrench between the collar nut and the spring perch, as the gouge marks aren't plainly visible there. You need to flip the second wrench in the opposite direction of the first so it bites into the tube, presses against the ground, and prevents the thing from turning while you use the other wrench on the collar nut.



    • Lay the strut assembly, which no longer has the spring and hat on it but still has the brake rotor, on the ground.
    • Get yerself two big-assed pipe wrenches.
    • Position one on the collar nut, the other on the body of the tube below the nut, both facing to the right, flipped in opposite directions, so the second wrench braces the tube against the ground and prevents it from turning.
      The two-monkey-wrench method of collar nut removal.
    • Lean on the first wrench with all your weight.
    • If the collar nut doesn't come off, heat it with a MAPP gas torch and try it again. I've never had one not come off, but some of them have been astonishingly recalcitrant.
      This collar nut on my 635CSi required multiple applications of heat and torque before it gave it up.
    • If the struts are the original oil-filled ones (which you'll know instantly because, when you start to withdraw them, they're narrow instead of filling up the entire tube), grab a tray or basin to catch the oil that is going to drip/gush from it when you withdraw it. You'll also want to tip the tube upside down to drain the oil out, then run a pole or wand with a wad of paper towels wire-tied to the end to give the bottom of the tube a cursory cleaning.
    • You may engage yourself in the third self-back-pat.



    Inspect the strut tower bushings and perch rubber. If you have reason to replace them, do it. Also take this opportunity to inspect the ball joint and its rubber boot. If you need to replace the ball joint, you have to go through this same procedure to undo the steering knuckle from the bottom of the strut assembly, so if there's anything wrong with it, now's the time to deal with it.


    Other Slippery Slope Stuff

    Hey, if you want to use this as an opportunity to remove the hub, replace the brake rotor and wheel bearings, and sandblast and repaint the strut housing, go for it. But that's not my jam. The undersides of my cars are never going to look like anything other than the heavily-used cars that they are.



    I could act like a repair manual and say that "assembly is the reverse of disassembly," but it never quite is.


    Strut Cartridge

    Thread the new strut cartridge into the tube and tighten it down. The torque spec I see here on the FAQ is 87 ft-lbs. That is tight. In comparison, the wheel lug nut torque is 59-64. And, unless you have Bilsteins and the tabbed ring tool, you're doing it with a pipe wrench, not a torque wrench . So... tight. Lean on it with a good portion of your body weight. You'll feel when it stops turning. I've never stripped one. Note that these collar nuts can loosen up, and they make one hell of a sharp banging over bumps when they do.


    Spring And Hat Installation

    • Slide the lower perch rubber back into the lower perch, taking care to seat the recess in the rubber properly in the perch.
    • Slide the still-compressed spring and compressor back onto the lower perch, taking care to seat the lower tail of the spring properly in the recess in the perch and the rubber.
    • Slide the upper perch and its properly-placed rubber over the strut piston, taking care to seat the upper tail of the spring properly in the recess in the perch and the rubber. (By the way, this is where a plate-style compressor really shines. Because the plates compress the spring squarely, getting the spring to seat properly requires zero work. With claw-style compressors, the spring is distorted, and this step is non-trivial.)
      Verifying that the top of the spring is correctly seated in the perch and its rubber.
    • Slide the spacer onto the strut piston.
    • Slide the hat onto the strut piston, first making sure that the dust cap that protects the bearing underside is in place.
    • Slide the three spacers (large, then tube, then small) over the strut piston and into the center recess of the hat.
    • Thread on the new Nyloc nut. When you tighten it, you'll have the same problem as removing it, which is that the piston will want to spin. Either use an impact wrench (on its lowest setting) to spin it on, or hold the top of the strut still with the appropriate wrench or Allen key. The torque spec I see here on the FAQ is 52 ft-lb. For comparison, that's less than a lug nut, so it doesn't have to be tightened with a pipe and a dying strain or anything.
    • Double-check that the spring tails are in their proper recesses in the perch.
    • Undo the spring compressor.
    • Spin the hat to make sure that it turns freely. It may be more difficult to spin than it was initially simply because the dust cap on the bottom is in a new position, but it shouldn't grind or bind.
    • Pat on your own back #4 is now in order.


    Strut Assembly Reinstallation

    • As I said, the strut assembly doesn't really weigh that much. It's not that difficult to just grab it, rotate the hat so the studs are correctly oriented (the two closer-spaced ones facing to the outside of the car), guide it into position under the fender, put the studs through the holes, and reach up and slide on a washer and thread a nut on one of the studs. Then you can let go and thread on the other washers and nuts. The FAQ lists the torque for the nuts as 18 ft-lbs.
    • Guide the bottom of the strut onto the steering knuckle so the slot and notch are aligned. 
    • There is some debate about using Loctite Blue (medium strength) on the 14mm bolts. Some folks use safety wire but no Loctite. Others, Loctite but no safety wire. Some folks use both. Personally, I use a dab of Loctite Blue on the threads of the bolts.
    • Thread the outer two bolts—the ones next to the brake shield—first, as they're the easiest to reach. Tighten them enough that they pull the steering knuckle and the notch square with the underside of the stud.
    • Then you need to center the steering wheel (if it's moved) and do the trick with the little floor jack under the end of the control arm to raise it enough to be able to, with your two index fingers, position the 3rd bolt in the recess of the control arm, guide it into the hole, and finger-tighten it.
    • Then snug all three bolts down. The torque on these 14mm bolts is only 18 ft-lbs. You can easily put a torque wrench on the two next to the brake shield, but the one above the control arm you need to tighten with a box-end wrench, so you have to do it by feel.
    • The safety wire and the tool to twist it to make it look pretty are available on Amazon and any number of other places.
    • Clean off the brake rotor with some brake cleaner, and reinstall the caliper. The FAQ lists the torque for the two 19mm bolts as 58 ft-lbs, fairly close to the lug nut torque.
    • Put the bolt, nut, and washer back on the plate holding the brake hoses to the strut housing.
    • Reinstall the sway bar end link bushing, retaining plate, and the two lock nuts.
    • Put the wheel back on and take the car down off the stands.


    That's it. You may self-administer the 5th self-back-pat.


    Alternate Method

    Above, I teased that it is possible to replace the strut cartridges without removing the strut assembly from the car—specifically, without unbolting the bottom of the strut housing from the steering knuckle. It is possible. I've done it. I wrote about it in detail here. You can leave the steering knuckle attached, but you still need to remove the caliper and unbolt the sway bar end link. The key is that the kind of plate-style compressor I've been using enables the possibility of doing this because the tightening mechanism is at the bottom. You can't do this with either my crank-style compressor or with the claws because, in both cases, the tightening mechanism is at the top. If you turn the claws over so the tightening bolt is at the bottom, the extending length of the threaded rod hits the underside of the shock tower.

    Compressor on spring on still-installed strut.
    Strut assembly swung out from under fender while still being attached to steering knuckle.

    The problem with this is two-fold. First, it is challenging to compress the spring, strut cartridge, and the hat so much that the studs on the hat clear the underside of the fender lip without scratching them. If you look carefully at the photo above, you can see that I've repositioned the compressor so that the lower plate isn't on the spring—it's actually below the lower perch. This was necessary to squeeze the spring down as much as possible to clear the fender lip.


    The other problem is that, once you swing the strut assembly out, you still need to undo the collar nut, and that is more challenging with the assembly hanging out in space than it is with it laying securely on the garage floor. In the above photos, I did it in my '72 tii. I was willing to try because, well, it's kind of a ratty car, so if I scratched the fender lips (which I didn't), I wouldn't have really minded. I was successful, but when I had to do the strut replacement in Hampton, my 49,000-mile 2002 (which is where the rest of the photos are from), I didn't want to take the chance, so I just removed the strut assemblies.




    If you do other wrenching, it's not really a big jump to replacing front struts. It's nothing to be afraid of. Borrow or buy a spring compressor, follow the directions, use common sense, and you're highly unlikely to hurt yourself.


    Now go forth and strut your stuff.



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    Great write up. If I do leave the strut attached at the bottom I have a old Crown Royal velvet bag I slip over the strut bearing to help prevent scratching on the fender wells and it adds a bit of class to the proceedings, this works well with lowering springs I would not recommend it with stock springs their just to tall IMO.  

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    Great write up, the 

    On 11/3/2021 at 12:44 PM, thehackmechanic said:

    appear to be largely gone from eBay. I can't say that I've ever used the clamshell, as it never appeared to be terribly substantial to me or to have a great amount of range.

    I tried one when I was doing a lot of suspension work on my car, it really didn’t work for a 02 due to clearance issues 






    after converting to adjustable spring perches my compressor was no longer needed




    Edited by chargin
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    Great write up on this, our experience  two days before loading our Baur on the truck to ship it to Europe for the Bavaria Tour and our European road trip one of the front shocks gave up and lost its oil…One of my friends who works for a local BMW shop said he would do it after hours the next day… in no more than And hour and a half he removed both front control arms whole compressed the springs on a bench compressor removed and replaced the strut and had it back on in 45 minutes…I always leave any work related to that spring to professionals…


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    Great write-up! Pipe wrenches did not work on my strut nuts, even an acetelyne torch did not help much (didn't want to get too aggressive though and dork the tube).


    The only way I could remove them was relieving the gland nut's grip by grinding reliefs just to the point of contacting the threads without marring them. Once paper thin you can peel the section away from the tube. I also notched the top rim and was able to chisel and air chisel them to make them spin.  One of the most siezed items I have encountered in 40 yrs of wrenching.

    The new nuts for the Bilsteins are provided (they sell a special wrench so you can torque them). 


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