Supporting the DeDion Tube with Radius arm and A-frame

This one is a retrospective blog, installation was completed back in Nov 2017.


Once I'd inserted the DeDion tube across the back of the car it was time to secure the component into place using the radius arm, and A-frame.


The newer pictorial manual or Ikea style manual as it is often referred shows the radius arm being attached first, and so that's the order which I used. Installation of the radius arm requires fixings at either end, the frontmost passing from the cabin out, whilst the rear goes from the outside in. Each radius arm also has a shaped surface helping to identify orientation. Just be careful not to damage the paintwork and the DeDion tube bracket can be a little tight to push the mount through. Having protected the paint and used a little wiggling to push the rear mounting home my experience fitting the radius arm was very straightforward.


I have read that some owners experience the radius arm bolts coming loose, particularly the forward one, which is later obscured by the car's seating, I guess we'll need to keep an eye on that.


Sadly I didn't take any explicit photographs of the radius arm install, but as mentioned it is pretty straightforward, so you should be fine.


Oh whilst I think about it. There are two forward mounting holes for the radius arm. The upper is for the S pack cars whilst the lower is for the R pack cars. At the point of writing, I don't have any information as to whether you can interchange, i.e. an R pack car could soften its ride comfort by using the S pack mounting hole etc. Some research needs to be done, maybe a follow-up blog!


Next the A-frame. The A-frame is a large triangular structure which attaches at either side of the car at the front of each rear wheel arch and then in the centre of the car at the rear. The rear connection attaches to the V-shaped structure welded to the bottom side of the DeDion tube.


As soon as I started working with the A-frame under the car I recognised how difficult it was to handle, it's not particularly heavy, just large and likes to rotate around in your hands. To help with the handling and positioning of the frame I loosely attached it under the car using some large cable ties, I basically hung the frame under the car, whilst I worked around each of the mounting points.

Cable tie used to hang the A-frame, also shows the rear connection on the DeDion tube with the plastic anti-squeak washers fitted.

Attaching the A-frame once hung was straight forward. The rear connection requires some firm guidance to push the joints either side of the mount at the bottom of the V, but there isn't anything to be concerned about. You do need to space the joint using large white plastic washers which are designed to prevent squeaking, other than that it's nice and easy.


Likewise, the front A-frame mounts are attached to the box section at the front of each wheel arch. Although it's a case of merely inserting a bolt, nut and some washers to hold the front in place the complexity here comes from the alignment of the A-frame. The A-frame needs to be central and equidistance to the chassis on either side. Spacer washers need to be added between the chassis and A-frame to obtain the correct spacing.

Alignment required. Image courtesy of Cateram Car's assembly guide.

During my installation, I required 4 on the near side and 5 on the off side. This resulted in 89.2mm on the near side and 89.0mm on the off side between the end of the tube and the chassis. I believe each spacing washer has a width of 2mm, so I concluded the install was appropriately aligned. Use of a set of digital callipers is really handy for this.

The assembly guide does a good a job of illustrating the required nuts, bolts and washers, however, it doesn't really do a fantastic job of illustrating the orientation of the A-frame itself. It might be worth noting that the frame needs to be installed so that the front mounts turn upwards when installed.


Hope that helps, next up, fitting the rear anti-roll bar or ARB.

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Loves cars, light weight specials, jDM, Lotus, Caterham, Rallying and Trackdays