The Big Book of Suspension Installation
Overview and General Information
I love my Z3 Coupe. One of the few things I have never liked about the car is the ride height. I think the car sits too high for such sporty and aggressive character. It reminds me of a Conestoga wagon. Here is the car in its stock form:
To solve the problem, I decided to replace the stock BMW Shocks and Springs with H&R Springs and Bilstein Shocks. The setup dropped the ride height from 24” in the front and 23.5” in the back (I measured from the bottom edge of the wheels, not the ground) to 22.5” in the front and 22 1/8” in the back. In the end, I am very pleased with the result. Here is how the car looks with the new suspension:
Here is a comparison of the height of the front end:
And here is the same comparison for the rear end:
Project Time and a Few Notes (After the Fact)
The total amount of time I spent on this project was: 8.5 hours
*I took my time, took a ton of photos, documented everything on paper and researched the project thoroughly. I have never changed a suspension before in my life, and only got basic pointers over the phone from my brother. I also spaced the project out over several weekends to cut down on time pressure and other factors. I got an estimate from several shops locally that were recommended to me and they all quoted around 6 to 8 hours of work for the installation with hourly rates ranging from $60.00/hr to $115.00/hr for the Ferrari mechanic. The Ferrari mechanic would not do the installation unless I installed Camber Correction Plates. Looking back on the project as a whole, it was well worth it and was an extremely good learning experience. When considering if this is a Do It Yourself project, keep in mind that it is probably too much work for one person alone, get a second set of hands for help. This project also requires a good amount of general mechanical ability. Take all of these factors into consideration before deciding on whether or not you want to tackle this project. Even if you do the installation yourself, you will still need to get the car professionally aligned when you are finished.
Words of Caution
Installation of suspension parts is extremely dangerous. You will need to use a Spring Compressor which a very dangerous tool. Improper use can and most likely will kill you or someone else or at the very least put a hole in one of your walls. Do not screw around with a spring compressor. Do not under any circumstances attempt installation unless you are absolutely sure you know what you are doing.
I want to mention right from the start that I did not document the installation of the rear shocks at all. I installed them just before Homecoming this past August and with everything we had going on, we were a bit pressed for time. I suggest taking the time to install Ron Stygar’s Rear Shock Mounts. The stock shock mounts require that you disassemble the entire trunk area of the Coupe in order to remove the shocks. With Ron’s Mounts, you no longer need to do this as you can now remove the shocks from underneath the car (Yes, you still need to take apart your trunk to get the stock shocks and mounts out). This will help you in the long run if you ever need to replace the shocks. The stock mounts are reversed from the picture, the bolts face up into the trunk area of the car with the nuts on the inside of the car. A big thank you to Ron for yet another excellent product! Here is a picture of the installed Stygar Shock Mount:
Rear Spring Removal
Jack the rear end of the car up and put on Jack Stands. Be sure to chock the front wheels to prevent the car from rolling. I like to leave the jack under the car with a minimal amount of pressure just in case something goes wrong. Remove the rear wheels. You will now be looking at the stock spring (I know, my car is dirty, don’t be too harsh!):
Unbolt the rear shock (18mm bolt) and use a jack to support the weight of the trailing arm (I did not completely remove the shock for this step). Also disconnect the Rear Swaybar Mount. The Rear Swaybar has a brake line that clips into a white holder. Be sure to disconnect this brake line at this time as well (it will pop right out). You will be lowering the trailing arm and you do not need any extra tension on that line. The Swaybar nut is a 13mm nut.
To remove the rear spring from the car, slowly lower the jack that is supporting the trailing arm. This will give you a small amount of play in the spring but not enough to remove it. Following the advice of both Shawn McCurdy and Dave Regis (I have included links to both of their excellent How-to’s at the end of my write-up but want to thank both of them again for a job well done), I used a prybar to gently pry the spring up. You may also need to push down on the trailing arm a small bit as well. Once you have the bottom of the spring free, the top is easy to get out. On the bottom and top of the spring are rubber “bumpers”, it is very clear which is which: the top has a fairly large ‘teet’ hanging down. I did not replace these as I am only at about 1500 miles on my car but it may be a good idea to replace if you actually drive your car (unlike me!).
Here is a picture of the Spring “Bumpers”:
The Rear Spring should now be removed:
Here is a side-by-side comparison of the H&R Spring and the Stock Spring:
Installation of Rear Spring
Clean up the Rubber “Bumpers” while you have the chance. Once clean, put them back in place. Now set the new spring in place. You will need to slide the top end of the spring over the ‘teet’ first and then bring in the bottom. You should not have any trouble getting the new spring in place, as it is quite a bit shorter than the stock spring:
With the spring in place, it is now time to put everything back together. Use the jack to raise the trailing arm up so that you can connect the shock. The bolt for the shock is 18mm and requires 77NM of torque. Take your time lining up the bolt, do not force it. At this point I did not connect the Rear Swaybar mount. I waited until I had the other side done and connected both as the last step.
You’re almost there! Repeat this process for the other side of the car.
Once the other side is complete, connect the Rear Swaybar Mounts. The nut is 13mm and requires 22NM of Torque. Secure the brake line in the clip and then bolt the mount in place.
So Now Then
Now that the rear suspension is complete, it is time to take the car off of the jack stands. Before doing so, take the time to clean the inside of the rear wheels and give them a coat of wax. I highly recommend that you place at least one 2”x6” or larger board under the rear tires before setting the car down. Your rear end is going to be riding over 1” lower and you want to make sure that you will be able to get the jack out from underneath the car. Installation of the rear springs took my dad and myself about 1.5 hours. Installation of the rear shocks (including disassembly and reassembly of the trunk area) took JonM and I around 3.5 hours, but we are pretty meticulous when it comes to interior parts and trim.
Installation of the rear springs took my dad and myself about 1.5 hours. Installation of the rear shocks (including disassembly and reassembly of the trunk area) took JonM and I around 3.5 hours.
Total Project Time so far: 5 Hours
That’s it, you are done with the rear!! Take the time to pull the car out of the garage, pop open a 40 of High Life and bask in a job well done.
Up Front…Front Strut
The following parts are needed if you are going to replace all of the hardware. We replaced everything so we did not have to disassemble the stock strut-spring units. Less time with the spring compressor is better, it will save time, and increase safety margins by using new hardware. The quantity listed is for both the left and right strut-This is the total amount you will need for the job and the price is the list price per item. From here on, I will refer to each by their name from the BMW EPC. Please note that many of the bolts, nuts and washers you remove to get the strut out are one use only (i.e. replace on installation of new strut). I highly recommend that you go ahead and buy these parts.
31 33 1 092 887 Self-Locking Collar Nut Qty: 6 $0.55
31 33 1 094 288 Washer Gasket Qty: 2 $3.35
31 33 1 092 885 Guide Support Qty: 2 $70.00
31 33 1 116 983 Flat Washer Qty: 2 $0.64
31 33 1 090 479 Spring Pad Lower Qty: 2 $3.35
31 33 1 135 580 Upper Spring Plate Qty: 2 $10.00
31 33 1 128 523 Spring Pad Upper Qty: 2 $4.23
31 31 1 136 465 Hex Bolt w/ Washer Qty: 4 $1.53
31 33 1 094 516 Self-Locking Hex Nut #2 Qty: 2 $0.45
07 11 9 905 853 Fit Bolt Qty: 2 $1.80
31 33 1 110 196 Dust Protection Collar $1.35
31 31 1 139 453 Covering Cap (Re-used)
33 18 1 181 310 Cable Holder (Re-used)
Removal of the front Struts
Begin by driving the front end of your car up onto ramps. Loosen the lug bolts on the wheels and jack the car up and place on jack stands. Remove the front wheels. You will now be looking at the front struts:
Begin by putting one of the lug bolts back in and tightening about half way. Use a very sturdy rope or wire to loop around the lug bolt and find a stationary place in the engine bay for the other end. I used the engine lift point that is towards the front of the engine in the center. The towel in the picture is merely to prevent any damage to car from the rope. This will help hold the weight of the brake/wheel while working:
Disconnect the brake lines that are attached to hangers on the strut (3 on the car side of the driver’s side-2 on the passenger side and the lines toward the outside of the car).
Now that the brake/wheel is secure, loosen and remove the 2 Hex Bolts with Washers (there is one on the other side of the strut not visible) as well as the Fit Bolt and Self Locking Hex Nut #2 (The nut is shown with the bolt’s head on the other side of the strut).
Once these are removed, loosen the Self Locking Collar nuts in the engine bay (they are located on the top of the Strut Towers-3 per side).
It is now time to remove the strut. I found that by lowering the strut down and towards the front of the car allowed the top of the strut to come out of the wheel well. The rest of the strut was easily removed. Be cautious of the brake lines throughout this step.
The front strut is now out of the car.
Build Up of The New Strut
Now that the stock strut is removed, it is time to build the new strut. Move into an area where you have a good amount of room and use of a vise if need be (The garage is not needed now). Lay out all the parts so that you have them and can reference them:
At this point, I removed the Cable Holder from the stock strut and put it in place on the new Strut (this is not a part that needs to be replaced but I have included the part number if you decide to use a new one):
Place the Spring Pad-Lower onto the bottom of the Strut. Be sure to line it up correctly, there is a 90-degree up bend in the strut that will correspond to the same bend in the pad. Place the spring onto the Pad to with the end of the spring aligned with the bend (The text on the spring should be right-side up):
Once the spring is in place, place the Spring Pad-Upper onto the spring noting the similar orientation of the 90-degree bend and then place the Upper Spring Plate on top of the Pad. The Flat Washer goes on top of the Plate:
It is now time to use the Spring Compressor. If you have any hesitation to use the compressor, do not. Replace the stock strut and let a professional do the rest of the work. A compressed spring has a tremendous amount of load on it, enough to go through you and probably a cinderblock wall. You could have a professional shop assemble the new struts with new springs if you wanted to. The kicker would be you’d need to buy all of the hardware like I did. Be very careful for the next few steps! If you are going ahead, place the spring compressor on the spring, I wrapped the ends of the compressor in duct tape to prevent any damage to the finish of the spring. This is not necessary and probably not recommended, but I waxed my new suspension parts so I went the extra mile.
Begin tightening the spring compressor. If your spring compressor is similar to the one I used, tighten 3 rotations of the wrench and then do the other side (Alternating between sides). Do not tighten one side and then the other! You should compress the spring until the Upper Spring Plate and Flat Washer is below the lowest thread. Here is the correct compression with the Flat Washer and Dust Protection Collar in place:
Place the Guide Support on top of the Spring Plate. The new strut will come with a nut that is 22mm that you should use. With the Guide Support and nut in place, use a 22mm Deep Socket on the nut.
To tighten the nut, you will need a 6mm Metric Allen Wrench. Place the 22mm Socket on the nut and slide the Allen Wrench inside the socket. The end of the threaded rod takes the Allen Wrench. The reason for the Allen Wrench is so that when you tighten the nut, you do not spin the threaded rod. You will need to turn the socket and hold the Allen Wrench at the same time. You may need to use a pair of pliers to hold the Allen Wrench. Since you cannot use a wrench to spin the socket, use a pair of Vise Grip Pliers to grip the side of the socket and turn while holding the Allen Wrench.
Once the socket is tight (The bottom of the Guide Support will butt up against the Blue Dust Collar on the Bilstein Strut) remove the Allen Wrench and Socket. Place the Covering Cap (I re-used this cap from the stock strut-I have included the part number incase you decide to replace it. The Covering Cap will pop right out of the stock strut, use a small flat blade screw driver to pry it off) over the area where the bolt is and then place the Washer Gasket on the top of the Guide Support:
The new strut is now assembled:
Installation of the Front Struts
On the bottom of the new strut there are 3 holes. The 2 outer holes are for the Hex Bolt with Washers. The hole in the center mates with a ‘nipple’ that is on the inside of the brake/wheel. This can be a bit of a hassle and gave us a fair amount of trouble our first pass. I had to file off some of the paint on the inside of the hole on the strut in order to get the nipple to fit. If you try to install the strut and have trouble, don’t worry. File a small amount of the paint away and it will fit fine.
To install the strut, bring the lower end in first (be aware of the brake lines!) and then bring the top in. This is the exact opposite of removal of the stock strut:
With the strut in place, put the Fit Bolt in first and then put the Self Locking Hex Nut #2 on loose. You should be able to get the two Hex Bolt with Washers in without any trouble. Tighten these three bolts. The Torque Value of the Hex Bolt with Washers is 107NM. The Fit Bolt’s Torque is also 107NM. You will need to use a wrench to hold the Self Locking Hex Nut #2 (Also 18mm) while you tighten the Fit Bolt. Both the Fit Bolt as well as the Hex Bolt with Washers are 18mm.
Reconnect the Brake Lines to their holders.
Move into the engine bay and put the three Self Locking Collar Nuts in place. Do not torque these down, we will get to them later.
With strut in place, move onto the other side and repeat this process. Take the time now to once again clean the wheel wells and the inside of the wheels. Once both sides are done, put the wheels back on the car, remove the jack stands and lower the car onto the ramps (You will need the ramps at this point for the same reason you needed the boards when doing the back, your car is going to be over an inch shorter and you want to be sure you can get the jack out from under the car). Once the car is on the ramps, tighten the Self Locking Collar Nuts. The Torque value on these nuts is 22NM and should only be applied when there is a load on the strut (i.e. the car should not be on jack stands or on a jack when tightening them down).
So Now Then
Pull the car out of the garage and pop open another 40 of High Life. You are finished! After installation of the new suspension, take your car to a reputable mechanic and have it aligned. This was a very long and drawn out modification but is one of the best mods one can do to their Z (aside from adding some Leather accents to the interior!). Installation of the front struts took my dad and myself a good 3.5 hours.
There has got to be a better way to do this. Hats off to you for posting this pic. I don't think I'd have the balls to admit I did it this way. Aren't there ratchets that have a hole in them specifically for this kind of operation?
very cool and informative Bently manuals doesnt have anything on you , glad you made it through the spring compression tool work all in one piece.
and the car does look so sweeeeeeeeett:thumbup:
If you're comfortable, you can actually cut a hole out of a long socket to do this, especially if the top collar nut needs to be tighted to torque.
One of the 'traditional' ways of dealing with that strut nut (dis)assembly is with an open-back angle wrench.
Sorry for the small pic but that's the first one I could find.
On some cars where that nut isn't recessed as much I've used an offset box wrench.
Also, I am VERY interested in this:
Because on the E46 wagon it requires the disassembly of essentially the entire rear interior of the car, and not just the peeling back of a liner like in sedan/coupes, something like this would be a godsend when it comes to shock replacement time.
Nice job Andy.
Question: since you were replacing most of the front strut parts anyway, why did you not elect to use the M version upper bearing to gain a little increase in castor and camber angle?
I am under the impression that they would interchange, but I've been wrong before...
Your Coupe definitely looks better closer to the ground!
I am still amazed at how good the car looks now. I guess I didn't really realize how bad it was before. I saw pictures of a Z3 with the stock suspension and 18" wheels on Toadfly, talk about a conestoga wagon!
More big things on the way in the coming weeks.
Are the parts the same for the M Coupe?
When I do my MCoupe will the parts# be the same?
Nice work & thanks for the gr8 writeup!
& here we thought you were just an interior decorator!;)
What are your oppinions of the handling before vs after the upgrade? Obviously it improved, but was it a marked improvement?
Moreover, how well does the Coupe handle less than perfect roads?
I drove an E30 325i Sport (which has, IIRC, an identical suspension design -- the trailing arms are identical) with H&Rs + Bilstiens and was very surprised how well it handled broken pavement. Granted, the E30 and the Coupe H&R kits probably run different spring rates, but I'm curious as to how well the Coupe kit fares.
I haven't spent enough time with the new set up to really answer whether or not there is a significant change in the ride. The weather got kind of nasty here so hopefully I will get a good break this week to put it through it's paces.
Re: Are the parts the same for the M Coupe?
Preliminary check (you should verify) is that your guide bearing #'s are:
LH 31 33 2 092 897
RH 31 33 2 092 898
Again, you should verify these numbers for your application.
BTW, unless you want to replace your upper guide bearing, your existing ones can be reused.
Compare Andy's upper guide bearing to one on the M version for reference to camber/castor change.
I found the H&R + Bilstien on the E30 to be a great combo. It'd be interesting to see how the Coupe compares. But, the aggressive look of a lowered stance seems to make the H&R upgrade worthwhile.
A low-mileage 2.8 Coupe is on my shopping list of things to buy when I graduate. They're getting pretty damn affordable!
>Originally posted by Randy Forbes
>Nice job Andy.
>Question: since you were replacing most of the front strut parts >anyway, why did you not elect to use the M version upper >bearing to gain a little increase in castor and camber angle?
>I am under the impression that they would interchange, but I've >been wrong before...
>Your Coupe definitely looks better closer to the ground!
>Randy, I never even thought about it.
For what it's worth, I did what Randy suggests on a 2.8 Coupe that I had. I replaced the front struts with ones from an M Coupe. The change made a major improvement in the car's desire to follow abberations in the road surface (tramlining, I think) and pull the steering wheel around accordingly. In fact, it practically eliminated this unwanted aspect of the 2.8 Coupe's driving personality. Alignment specs became an M Coupe's with no further issues to deal with. The only difference noted was that the steering effort became a little firmer, which I didn't mind at all.
I think your car is better looking than mine. I think Z3Cs look nicer than MCs in general.
I am p/ssed.
Maybe I should buy a set of Z3 gills.
Any word on the Yellow belts?:dunno:
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