Project E46 M3 - Differential Bushings December 16 2024
Even with only 70,000 miles on our E46 M3, the differential bushings were toast. BMW used foam as the bushing material, which gets crumbly over time. Worn differential bushings can lead to a clunking sound when the driveline is loaded and unloaded. This is how we changed our differential bushings. Note that the rear subframe is unique to the M3 models and is different from the other E46 models. This mainly affects which tools are needed for pressing out the bushing. We had to make custom tools to accommodate the weird geometry of the rear subframe.
Before we get started and lift the car off the ground, it can be helpful to first remove the two outboard bolts of the V-brace. If you are using jack stands or a lift to support the car in the air, they may get in the way of removing the V-brace bolts, as the jacking points are very close to the V-brace bolts. Remove the 2 bolts near the jacking points, one on each side of the car. There is a remaining center bolt that will hold the V-brace to the chassis.
Also note that you are going to have to be able to get the car relatively high in the air so that the differential has enough room to exit the chassis. We used a QuickJack 5000TL with a max lift height of 24 inches, and had enough room for the job.
With the car safely in the air, remove the final bolt for the V-brace from the center.
With the V-brace out of the way, we can start removing the plastic under panels. There are 2 small plastic triangular trim pieces in front of each rear wheel. Each trim piece is held in by 3 plastic rivets. We used a pry tool to pull up on the center stalk of the rivet, and the rivet was unlocked and free to be pulled out. It can be helpful to have new rivets on hand, as the rivets can be brittle from age.
The two larger plastic under panels were also removed. There are screws around the perimeter.
On the left hand side of the car, there is one fastener that is hard to access. We will have to come back to this fastener after we have removed some other parts to gain access.
We then turned our attention to the exhaust. We only removed the section between the catalytic converters and the muffler. The forward end has six bolts. We replaced the nuts with new ones while we were in here because these bolts in particular like to corrode.
On the aft side, we removed the 4 bolts to the muffler.
The last things holding the exhaust up are the support brackets. Remove the brackets and the exhaust section is free to be removed from the car.
With the exhaust section out of the way, we can go back to remove the one last fastener holding the left underbody tray on.
With the exhaust section out of the way, we can now remove the heat shielding. There are 4 screws (10 MM).
We then disconnected the input flange from the differential. It helps to have the parking brake set and/or the transmission in gear so that the driveshaft doesn't spin while you try to loosen the bolts. Remove the accessible bolts and then release the parking brake and put the transmission in neutral to enable you to turn the driveshaft and expose the previously inaccessible bolts. Set the parking brake or put the transmission in gear to lock the driveshaft in your new desired orientation.
After the driveshaft is disconnected, support it from below with something like a cardboard box or suspend it from above with string or stiff wire. We covered the end of the driveshaft with a plastic bag and rubber bands to keep debris out of the grease.
We then disconnected the axle half shafts from the differential. To loosen the bolts, the axles were locked in place by setting the parking brake and loosening the accessible bolts. To get the remaining inaccessible bolts, we then released the parking brake and turned the axles to expose the remaining bolts and then locked the axles in place again with the parking brake. We did this on both sides of the car.
We needed to remove the swaybar to allow egress of the differential. We undid the swaybar end links on both sides. You have to get a wrench to hold the bolt on the top side while loosening the nuts on the bottom side.
We then undid the swaybar mounts. With all the bolts out, you can maneuver the swaybar out.
We then turned our attention to the heat shield over the subframe bushing.
With the heat shield off, we can now access all the bolts of the cross brace. Remove the bolts and remove the cross brace.
If you are going to replace your differential fluid, now is a good time to drain the fluid while the differential is still bolted to the chassis and you can more easily apply torque on the drain and fill ports. Make sure you loosen the fill port first! If you open the drain port first, you run the risk of draining your differential fluid and finding out later that you can't fill it because something is wrong with the fill port. To drain the differential, place an oil collection container under the drain port and remove the drain plug. Replacing the drain plug and fill plug with new plugs is recommended because reusing the old plugs has the potential to leak.
We will refill the differential after the bushings have been replaced and the differential is mounted back in the chassis. We want the differential to be empty so that it doesn't spill everywhere when we start replacing seals and removing the rear cover.
There are three bolts holding the differential to the rear subframe. 2 on the aft end and 1 on the forward end. The 2 on the aft end are shown below. Remove the bolts.
There is one mounting bolt on the forward side of the differential, shown below. Remove the bolt.
With the differential now free, we then had the task of getting this ~80 pound lump of cast iron out of the car safely. A transmission jack is definitely recommended. It also helps to have a second set of hands. If this differential falls on you, you will likely sustain a severe crush injury. This thing is seriously heavy and awkward, and you will be in an awkward position! We used a floor jack in conjunction with some ratchet straps to get the job done, but it was sketchy. With the benefit of knowing what we know now, we wouldn't attempt this method again. At a minimum, we would opt for a transmission jack adapter that can work with our floor jack. The differential has to tilt nose up as it comes down to clear the spare tire compartment.
With the differential out, we removed the differential cover which allowed us to place the differential cover in a shop press and press out the bushings. If you have a bushing removal tool, you can change the bushings without having to remove the differential cover. Note the oval hole and the orientation of the oval for reinstallation.
If you prefer to have a slightly stiffer and longer-lasting bushing, the rubber E36 M3 bushings can be used on the aft 2 locations. We used BMW part number 33171134872. Note the orientation of the bushing before installing. It is possible to install them flipped the wrong way. Shout out to our good friend and differential expert at Wanganstyle Global who made this recommendation. He builds performance differentials, often for endurance racing applications. He can swap in different ratios, install a specific LSD or rebuild your differential and ship it to wherever you are.
With the new bushing pressed in and the old gasket material removed from the sealing surface, we used some Permatex Ultra Black RTV to seal the differential cover back on to the differential. Our friend at Wanganstyle Global recommended RTV over using the paper gasket, citing more reliable sealing.
The forward differential bushing resides in the rear subframe. There is a protrusion on the subframe structure, outlined in red. This gets in the way of most standard bushing removal tools. We weren't able to find a tool specific to the E46 M3, so we had to create a custom tool to match the specifics of this situation.
This is how our tool looked like in action. Note the notch cut out of the tool to clear the subframe structure. We added a lip to the tool so that it sits exactly where it needs to sit without needing to guess at the alignment. The bushing came out smoothly and without a fight.
To install the new bushing, we created a custom installation tool again because there was some funky geometry going on, and a standard bushing press tool would run into interference issues.
This was the tool in action. The bushing went in smoothly and without struggle. Note the groove on the tool so that it aligns to exactly where it needs to be.
With the bushings replaced, we can button everything back up. One thing to note is the original bolts that secure the aft two bushings have been superceded with a new bolt. The new bolt has a longer shank, which is stronger and doesn't place the threads on the bearing surface. We used BMW part number 23001222891.
One small challenge we encountered was there wasn't enough room to get the right hand side half shaft mounted back onto the differential. Supporting the differential with a jack, loosening the front mounting bolt and removing the rear mounting bolts enabled the differential to be shifted around enough to get the half shaft to mount.
With the differential back in the chassis, we refilled it with Redline 75W140 differential fluid. With the drain plug tightened and the fill plug removed, we pumped differential fluid into the fill port until it began to overflow. We then put in the fill plug and tightened it.
The rest of the reassembly is the reverse of disassembly.
With the new bushings installed and new differential fluid, the car seems to shift smoother and there is no clunk coming from the rear between shifts.