BMW DIY Video – Replacing Rear Trailing Arm Bushings, RTAB, Stock, Powerflex and Ultimate – E36 E46 E83 E85 Z3 Z4 X3
This article will discuss the function of the trailing arm bushings and how to replace them, in our DIY video. Continue to the text below the video link for a description of the function and the failure modes of the Rear Trailing Arm Bushings (RTABs).
In replacing the RTABs, we have various options on the replacement parts:
* Stock replacement - These bushings are available as either Genuine BMW or various other quality aftermarket manufacturers.
* Urethane upgrade - Installing urethane RTABs will provide a tighter control of the trailing arm. Not only will the rear suspension feel more “planted” in spirited driving, the steering inputs will feel more direct as will transitions between braking and acceleration.
* Ultimate RTAB upgrade - The Ultimate trailing arm bushings provide all of the benefits of the urethane upgrade bushings along with full articulated spherical bearing action, while still damping vibrations through the chassis. The Ultimate RTAB uses a fully articulated suspension bearing installed in a billet housing. This design eliminates all flex yet provides 100% articulation of the trailing arm.
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Follow along with our DIY video as we discuss the different bushings and show how to remove the old bushing and install the three different types of new RTABs. We will be performing this install on an E36 M3. We will show the install steps for each type of bushing, but the final install will be with the Ultimate RTABs. The applicable Bentley Publishing repair manual will detail model and bushing type specific steps and procedures.
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On the BMW models noted in this article, the rear suspension hub assembly is incorporated into a larger cast iron suspension assembly that we just call the rear trailing arm. The trailing arm is attached to the vehicle chassis and articulated via two lateral control arms (upper and lower) and a forward longitudinal pivot point at the front of the trailing arm. As with all of the connection points for the control arms (to the trailing arm and the chassis), the forward pivot point uses a large bushing for attachment to the chassis as well as allowance for articulation. As the wheel moves up and down during suspension movement, the forward trailing arm bushing becomes the pivot point. Additionally, the forward trailing arm bushing is performing the task of locating the rear wheel longitudinally and through this, also absorbs the majority of the torque loads that are transmitted from the tire’s contact with the pavement and ultimately into the chassis. In other words, the bushing is the contact point for the positive loading under acceleration and the negative loading during braking, keeping the wheel in place on the vehicle.
With the above points noted, the Rear Trailing Arm Bushing (RTAB) is a highly stressed suspension component. As the RTABs age, the vehicle will feel less secure on the road. The rear of the vehicle can move around as the torque loads of acceleration and braking act on the bushings, effectively steering the vehicle from the rear. As the bushings continue to age, a clunking can be experienced as the vehicle goes over bumps or transitions between braking and acceleration. Note that these symptoms can be present, yet a visual inspection of the bushings may not show any apparent problems. The bushings are simply too soft at this point.