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Rear Subframe Reinforcement Plates and Sway Bar Reinforcement

Warning: If you are not competent or do not feel comfortable doing any of these modifications or procedures, then please do not do so. I will not be held responsible for any damages caused by a result of your actions. Now on to the fun stuff!

Materials:

Bushings
[list for my 328, M3 parts may be different]
1 Front Differential Mount Bushing (Part Number 33 17 1 134 910)
2 60.5 mm Front Subframe to Chassis Bushings (Part Number 33 31 9 059 300 (pair))
2 62.5 mm Rear Subframe to Chassis Bushings (Part Number 33 31 9 059 301 (pair))
1 Subframe to Differential Hex Bolt with Washer (Part Number 33 17 1 094 398)

Top Left: Differential Mount Bushings
Top Right: Rear Subframe Bushings
Bottom Left: Front Subframe Bushings
Bottom Right: Front Differential Bolt

(I don't know why the diff bolt is threaded at the top)

Chassis Reinforcer Plates
[these are M3 parts]
'Spacer Ring' Front Left (Part Number 41 00 2 256 495)
'Spacer Ring' Front Right (Part Number 41 00 2 256 496)
'Spacer Ring' Rear Left (Part Number 41 11 2 256 497)
'Spacer Ring' Rear Right (Part Number 41 11 2 256 498)

Sway Bar Reinforcement
8"x1"x1/8" Steel Stock (this is just what I had around, something longer, thinner, and less wide would work)

If you don't want to make anything, Ground Control and Turner Motorsport each have some reinforcers available.

Tools:
Wrenches and Sockets (air tools always help)
Jack and Jack Stands or lift
Grinder (I used a die grinder with an abrasive disc, it removes paint and other crud very easily, but not metal)
Welder
Paint
Press (for bushing install)
Muscle, this one's not easy!


Procedure:

Subframe Removal
1.) Chock the front wheels, jack the car up, and support it with jack stands or get it up in the air with a lift

2.) Remove the rear wheels

3.) The brakes can stay on here, I chose to remove mine at the time so I could adjust and lube the parking brake. I also investigated removing the parking brake cable all together, but couldn't get it out. This would allow complete removal of the suspension.

4.) Remove the muffler from the cat. Start with the bolts at the cat pipe. You'll want to give them a good soaking with some penetrating oil. Mine came off fine despite never being removed (surprised me!). Then you can move on to the rear mounts. Just remove the two nuts that hold the mount to the chassis. The easiest way I've found to get the muffler out (if I can stand under it, is to support it towards the center of the can and just drop it down and back. If it's on the ground (jackstands), a foot can help support the pipes.

5.) Now remove the two screws that hold the heat shielding for the exhaust on. They're in the top right of the picture above.

6.) You should be able to reach up past the driveshaft and unclip the parking brake cable from the mounts in the tunnel. This will give you more slack to move around the suspension once you get it off the car.

7.) Remove the lower shock bolts at this point to decompress the springs a bit. Remove the springs.

8.) The anti-sway bar can come out now. Start by removing the two nuts behind the spring (towards the center of the car). Then remove the mounts on the subframe. Then pull the bar out. While you're in there disconnect the wheel speed sensors and the one brake pad wear indicator from the plastic black box.

9.) Now the differential can come out.
a.) Remove the wheel speed sensor from the back of the differential by the fill and drain plugs.
b.) Remove the driveshaft bolts and loosen the front differential mount bolt.


c.) Remove the torx bolts holding the CV joints to the differential.


(if you were wondering, that's what a leaking output shaft seal looks like)

d.) Then move back to the two rear ear type mounts and loosen the bolts.


(rear subframe to chassis mount is also shown)


e.) You might want to use a jack to support the diff or you can just use your chest. It's not too terribly heavy, but I wouldn't want to drop it on my foot! Remove the front diff. bolt and then the two rears and pull the diff out. You might need a little of that muscle here.

10.) With the diff out of the way, you can move on to the suspension. You will have to remove at least one side of the suspension. I pulled the left hand side and left the right in. With both sides in, I wasn't able to get the subframe out.

11.) Start with the two bolts holding the two control arms to the subframe. Then move to the three trailing arm bolts that hold the RTAB cup to the chassis.

12.) At this point you should be able to move the suspension out of the way. You may need to remove the brake line bracket from the control arm and remove the caliper also to get enough room for the suspension to hang out of the way.

13.) Remove the two control arm bolts from the subframe.

14.) Now just remove the 4 bolts/nuts holding the subframe in and yank it out. Be sure the wheel speed sensor and other wires are all disconnected from the subframe.

15.) If you're doing the plates, go ahead and pull the studs at the front subframe mounting points.

Bushing Replacement

I didn't think this would be too bad, but I was wrong! Getting the bushings out wasn't too terrible, but I planned on pressing the new ones back in with a vice. Didn't work. I had to take them to a local machine shop and get them pressed all the way in. I got them about 2/3- 3/4 of the way.

The first option here is to get the bushings and take it to a machine shop. Have them press the old ones out and press the new ones in.

Option two is to get the bushings out and have a shop press them back in. This is basically what I ended up doing.

So, how'd I get them out? A drill, chisel, hammer and well that thing called muscle. It really wan't bad at all. I tried to them press them back in with a vice, but they're just too large and my vice is too small to get the job done. Once I got them partially in I took them to a local machine shop where we pressed them the rest of the way. Just as a note, a flat piece of metal was used to press the bushing in and a cup on the other end for the rubber to slide out through.

Sway Bar Tab Reinforcement

With the newly installed subframe bushings, I moved on to the reinforcements. As a note, these will need welded in. A muffler shop might be able to help you out with that if you do not have the necessary equipment. These really are not necessary for factory sway bars, but I figured I might as well do them while the subframe's out. It can be done while in the car, but it's a whole lot easier with it out of the car.

Ground Control and Turner Motorsport both have kits that they sell, but what I made does the same basic thing. What'd mine cost? A little time with a hammer and some spare steel I had around.

I'm just going to provide some pictures here, it's all pretty self-explanatory if you ask me. If you're confused, shoot me an email.

Chassis Reinforcment ('Spacer Rings')

These are parts which are installed on the M3, but not on the non-M cars. With stiffer suspension, hard driving, track time, autox, and time the chassis area can fail resulting in a tear around the subframe mount. Doesn't sound like fun to me. So in these go.

These do require welding, so you'd better know somebody who can weld or else hire a mobile welder to come to your house because your car is not going anywhere to install these once the subframe is out.

If I need to tell you how to weld these in, then you need to get some help and let a professional do the job. Never the less, here are a few pictures to highlight the whole ordeal.

I don't have any pictures of the rear plates, welded in, or after painting. The picture in the bottom right corner shows the fully welded RTAB cup threaded inserts. Some cars may have just been spot welded which can lead to failure. Crazy alignment tech's with impact guns do not help the situation either.

Subframe Post Painting

I just removed some of the rust and gave it a quick spray with some DPLF 90. That should keep the rust at bay for a few more years. The plates got the same treatment.

Reinstallation

Basically, the installation is just like the removal.

Don't forget to get an alignment. This will also raise the rear ride height slightly. I plan on adjusting the perches to get back to where the suspension was set.

Update [05.19.04]: After thinking about the anti-sway bar tab reinforcement, I don't think I have the plates in the optimum location. I think it would be better to have taken them all the way out to the other edge of the tab. Not a big deal I suppose just because I'm not running a larger bar. If I do go over to something bigger, then I'll just weld another tab on to the other edge.

 

 


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