Lighten up! R56 cast aluminum rear trailing arm conversion for the R50/53 MINI
By Ryan Malcolm (aka Ryephile)
Photos by the Author
MINIacs are a strange bunch. We spend crazy amounts of time and money on modifications to squeeze just a bit more performance out of our little hot-hatches. To take a page from Lotus founder Colin Chapman's ethos, lighter is quicker. When the new generation "R56" MINI was brought onto the market, us R53 owners were a bit jealous to hear the new car was a bit lighter than our beloved first generation MINIs. Lucky for us, with the help of fellow cutting-edge MINI enthusiasts, we discovered we can shed precious pounds off our R50 and R53. One of the best places to reduce weight to improve handling and ride is where there is unsprung mass. This includes wheels, brakes, and suspension pieces. The rear trailing arms from the R56 are close to a bolt-on conversion, however the parts list is exhaustive and the conversion is shrouded with cross-generation mystery. The benefits however, are a 12 pound overall weight reduction, improved rear suspension articulation resolution, and for early R50/53 chassis a much improved rear trailing arm pivot that reduces binding.
The conversion begins by getting all the new parts together. Simply put, everything that touches the old steel trailing arm needs to be replaced. The things that do carry over are minimal; the brake components, wheel bearing hub, lateral control arms, and shock absorber. The new parts needed include:
*the new cast aluminum R56 trailing arm of course!
*the main pivot bushing and carrier that bolts to the body and the bolt that goes into the trailing arm
*new upper and lower lateral control arm hardware, including the eccentric cam bolt to adjust camber
*new brake caliper mounting bracket bolts
*new wheel hub bolts
*lower shock absorber mounting bolt, and a machined adapter to mount R50/53 dampers to the beveled recess mount of the R56 trailing arm. The only readily available adapter I'm aware of is easily purchased from the great guys at Helix13.com
*R56 ABS wheel speed sensors
Once all the new components are gathered, we can begin taking off the old steel trailing arm assembly. Begin by unclipping the hydraulic and ABS lines from the shock absorber body. Unbolt the ABS sensor from the trailing arm, pull it out of the trailing arm, and unplug it from the main wiring harness. Next remove the brake caliper, bracket, and rotor. Hang the caliper with a stiff wire such that the brake line isn't stressed. Clean up the brake bracket and rotor, as they'll be reused with the new trailing arm. Now move under the car; take a permanent marker and trace around the trailing arm bushing mount that bolts to the body. Doing so will give you a visual guide to keep the alignment close to original. The next few steps can be completed in whatever order makes you feel good. The trailing arm mounting bushing's three bolts to the body; the lower control arm hardware to the trailing arm; and the lower shock absorber bolt. The trailing arm, bushing, and wheel hub should fall into your caring arms now!
Before we go throwing the new lightweight R56 cast aluminum trailing arm onto your MINI, we need to perform some preparatory work. Unbolt your original wheel bearing hub from the old steel trailing arm. Take a few minutes to clean it up. If you're a bit obsessive compulsive like I am, and it's likely, take a wire brush to your wheel hub to clean off the rust. Finish it off with some high temperature paint to protect it from rusting in the future. Mask off the rotating hub surface itself so you don't cause any wobbling in your brake rotors. If you're feeling ambitious, do the same to the brake rotor and caliper mounting bracket. Be sure to not get paint on the rotating machined mounting surfaces! Before the new trailing arm can be used, there is a snag. The R56 appears to use a different anti-roll-bar drop-link which has longer threads. This is manifested by a cast-in stanchion. There are two options; buy R56 anti-roll-bar drop-links, or shave off the cast-in stanchion. I chose the latter as I already had a set of brand-new ALTA drop-links on the shelf waiting for action. Pick your favorite course and we’re ready for installation.
It is now time to install the new R56 components. Begin by threading the self-tapping bolt through the trailing arm bushing mount into the trailing arm. Since it is self-tapping, be very careful to thread the bolt on-axis, and take your time to get it right the first time. Don't tighten it down fully yet, just a light snug. Next, bolt up the wheel bearing hub using the four new longer bolts, and the new ABS sensor using the old bolt from the steel arm. Take this assembly and bolt up the bushing mount to the body with the three bolts. Align the bracket to your marker outline as accurately as you can. Now bolt up your lateral control arms to the trailing arm, assembling the eccentric bolt assembly on the lower control arm pivot. Be sure to route your brake lines so they're running the same way they were, which is between the two control arms. At this point, take an educated guess regarding the eccentric camber adjustment bolt. If your rear camber was aligned to your preference, rotate the eccentric so it's in the middle of its lateral adjustability before tightening it down. Next, bolt up the brake rotor, the caliper bracket using new longer bolts, and the caliper using the existing bolts. Place the Helix13 shock absorber adapter into the aluminum trailing arm and thread the new self-tapping bolt through the shock absorber and adapter into the trailing arm. Be careful to align it on-axis just like the trailing arm bushing bolt. Torque this down snugly, ensuring the adapter piece seats properly. At this point, now that the trailing arm is about at ride height it’s time to snug down the trailing arm bushing bolt that we left a bit loose earlier. Plug in the ABS sensor to the body wiring harness and clip the lines to the shock absorber body. Now go around and double check everything is tightened down and looks good.
You should be ready to go! I urge everyone to align their rear suspension after this procedure; whether you have the tools yourself or bring it to your trusted alignment shop. I recommend zero toe and about -1.0 degree of camber, however everyone's preferences and applications are different; experts will already know what alignment settings they prefer.
What are the real-world benefits of the R56 trailing arm conversion? On the racetrack, the conversion seems to allow the car to rotate through corners easier and with better communication to the drivers’ seat. The revised pivot compared to 2002 and 2003 model year MINIs will unveil this change as a welcome improvement. On the street, the car feels more predictable while having a more compliant ride quality, mostly due to the reduced weight. The total cost for parts is approximately $750 if you purchase through a discount dealership like Classic MINI, my personal favorite. Depending on your skill level and quickness, this conversion should take the shade-tree mechanic about two evenings. Professional shops should only need a few hours of labor for the conversion. Whether this conversion is right for you is dependant if you've already read this far in the article! 12 pounds of important weight savings for $750 sounds either expensive or a good value depending on your perspective. At the very least, it's one more obsessive compulsive treasure to check off your MINIac list. Enjoy your newfound precision and lightness!
Quantity Description Detail Part Number 1 Trailing Arm - Aluminum Left 33-32-6-795-659 1 Trailing Arm - Aluminum Right 33-32-6-795-660 2 Self tapping Screw M14x1.5x101 33-32-6-770-089 2 Bushing Stopper 33-31-6-761-779 1 Bracket, trailing arm Left 33-30-6-799-089 1 Bracket, trailing arm Right 33-30-6-799-090 2 Hex Bolt with Washer M12x1.5x83-10.9 33-30-6-768-048 2 Self Locking Collar Nut M12x1.5-10ZNS3 33-32-6-760-374 2 Hex Bolt with Washer M12x1.5x100 33-30-6-772-658 2 Adjusting Plate 33-32-6-767-869 2 Cage Nut M12x1.5-10ZNS3 33-30-6-770-138 8 Hex Bolt with Washer M10x75-10.9 33-50-6-771-928 2 Rotational Speed Sensor Rear axle 34-52-6-773-020
In addition to the above MINI parts you will need one set of R56 Rear Shock Bushings, Helix Part Number HMS 1080.
Many Thanks to “blumini” for his excellent help and being a pioneer in this great adaptation of new technology.
Updated 4/16/15 With latest Part Numbers - Thanks to cct1
1st Gen "How To" Lighten up! R56 cast aluminum rear trailing arm conversion for the R50/53 MINI
One of the best places to reduce weight to improve handling and ride is where there is unsprung mass. This includes wheels, brakes, and suspension...