Insane In The Subframe: A DIY

Insane In The Subframe: A DIY

With our latest addition to fabrication, we figured it’s about time we made another good ol’ fashioned DIY.

Last time we had an E46 M3 in the shop for subframe reinforcements, we also had to replace a good part of the M3’s body, making for an incredibly intense job that’s usually much easier if caught earlier. Thankfully, we have an E46 M3 in the shop right now for that exact thing; this Carbon Black M3 is still in great shape, but the owner is looking to get the reinforcement kits installed before anything bad happens. He’s also in for a nearly complete bushing replacement, but we won’t be covering that in this first part of the DIY.


Your first steps will involve getting things out of the way. The subframe will be dropped with the drivetrain components (differential, axles), suspension components (control arms) and wheel hubs still attached, so it’s time to start getting things out of the way of those parts. First up is the exhaust. After disconnecting the battery and putting the car on a lift, remove the necessary shielding and bracing from the vehicle’s underbody. Disconnect the oxygen sensors and unbolt the exhaust from the body, as well as from the headers. Put it aside, preferably somewhere you won’t trip over it. If you want to trip over it, hey, that’s your prerogative, we’re just saying it’s probably not the best idea.


With the exhaust out of the way, it’s time to remove the brake calipers. The calipers are connected to the vehicle’s body by way of the brake fluid line, and since a fluid flush is unnecessary (and, might we add, additional labor hours that can cost you money), we’ll be showing you how to move the caliper out of the way. Start by removing the rear wheels. From there, you’ll remove the two bolts that hold the caliper and caliper bracket in place. At the same time, remove the bolt holding the bottom of the shock in place. You can leave the shock in place, just unbolt the bottom.


You’ll note that there are two wires coming off the passenger side hub assembly, and one wire off the driver’s side. The blue wire on both wheels is the wheel speed sensor, and the green wire that connects to the brake pad is for measuring brake pad wear. Follow these lines forward on the vehicle (you will have to remove a couple underbody panels) until you see their respective harness clips. Disconnect the clips; if you forget this, the wheel speed sensor wires will be forcefully removed when dropping the subframe, and that is not good.


With the sensors disconnected at the body, remove the caliper from its home and, using your hex keys, remove the two bolts that hold the caliper’s bracket in place. Remove the two brake pads (WATCH OUT for the wear sensor on the passenger side) and the caliper bracket. This gives you enough space to sneak the caliper between the axle and the lower control arm, allowing the subframe to drop without the calipers. Use your preferred method and location for hanging the calipers out of the way — we recommend zip ties or a wire hanger. You can also remove the brake rotors, but you don’t have to if you don’t want to.


At this point, you’re almost ready to get the subframe out. But wait! There’s still a massive driveshaft connected to the differential. So, after removing the necessary shielding, you can unbolt the guibo on the differential side. You can get the driveshaft moved in one of two ways. First, unbolt just the driveshaft’s center bearing, and use a bungee cord to move the driveshaft out of the way, leaving it bolted to the transmission-side guibo. Or, if you want to get it all the way gone, feel free to unbolt the whole darn thing and place it wherever you choose.


Aside from the mounting bolts, the only other things connected to the subframe assembly right now are the emergency brake cables. Since they’re nigh impossible to remove from the rear hubs, instead it’s time to move back to your interior. Remove your center console and disconnect the e-brake cables, making sure they can be slid out to the underbody. You can do this first, too, if you’d like. This can happen anytime prior to the actual subframe removal. It can happen two weeks before if you really want, but we don’t suggest operating a vehicle without a functional emergency brake. Safety first.


With the emergency brake cables disconnected, it’s time to get that subframe out. Find yourself a suitable transmission jack (it’s the easiest to utilize here thanks to its flat platform), position it underneath the differential and strap it down tight. From there…


…You’ll have to wait until tomorrow to find out what happens next. We’ll see you back here tomorrow, when we’ll drop the subframe and prep the body for the reinforcements. Until then, have a great day!

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  • bob mack
    Posted at 16:38h, 16 January

    Just found this while looking at buying a 2004 m3. Great job with the step-by-step. It’s going to make my job a lot easier.

  • fluidmotorunion
    Posted at 11:05h, 18 January

    Thanks Bob, congrats on your M3!

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