Caterham 420R Build: Rear Damper Part 3 + Radius Arms + A Frame (2025-08-04)

Before I start this session, I want to mention I did an off-camera session where I attempted to remove the bolt from the seat rail I had screwed up in the previous session.

I ended up having to cut the cap off with an angle grinder. Turns out, I did indeed shear off the nutsert that was welded to the rail.
I will have to get a new rail.

Today I got the sleeve bearing that I was missing for the rear damper, and I finished installing that. Very straightforward like the previous session.

The radius arms are next. Bolting the front to the chassis you have 2 options: a lower mount and an upper mount. The upper is for S pack cars. The lower is for R pack and Academy cars.

For all bolts in this session, I decided to apply copper slip. Also, all the washer chamfers face in towards the bushing, much like the front suspension had.

The rear bushing on the radius arm slots into the DeDion tube. The tolerance is pretty tight, I ended up smacking it with a mallet to get it in.
Once in, PAY attention to the bolts. There are 3 bolts that are the same threading. The two shorter ones are for the radius arms.The longer one is for the A Frame to DeDion. Don't make the same mistake I did and have to undo work.

The manual is a bit confusing on how to do the washers for the A Frame. One of the goals for the A Frame is to make sure the protrusion of the DeDion tube is equidistant on both sides. Let me simplify the washer situation:

The rear mount of the A Frame to DeDion just has white nylon washers. One each.

The front two mounts of the A Frame to the chassis are where you use a variable number of washers to space it out correctly.

For the rear mount, you'll need two sockets that are relatively thin-walled, because the bolt and nut there are in a pocket.

For the front two mounts, I've read that other people used 4 washers on the driver's side, and 3 washers on the passenger side.

I could only get 4 washers and 2 washers respectively. This didn't make my DeDion protrusion equal. I took one out on the driver's side and ended up with 3 washers on the driver's side, and 2 on the passenger side.

That got me to about 3.5 inches protrusion on both sides. Being worried that I'm missing about 1 washer's width in the system, I messaged my dealer. He said it'll be okay, but if I want to, I can use some of the thinner washers to fill it out.

Finally, don't do what I did and torque up the radius arms right away. For the suspension, you want the car resting on the suspension before torquing. Knowing this, I moved the jack stands to under the DeDion tube to torque the radius arms.

I then moved the jack stands BACK to the chassis rail, as the car was a bit wobbly when I was working on the A Frame... only to realize... I have to move the jack stands AGAIN to torque up the A Frame. Not the biggest deal, but save yourself the time, and wait until all the rear suspension is done up before torquing.