Fitting adjustable suspension

When I specified my options for the car, I made a few choices which had an unintended consequence that would not become clear until I had finished the build. My very low ride height has bothered me when out driving, and I’ve had a couple of light scrapes over speed bumps, especially those very narrow-width ones in car parks, and parking at the Goodwood Festival of Speed was an exercise in angles, approach and crawling over uneven surfaces that got tiresome quickly. Speed bumps are one thing, but my bigger worry is hitting something at speed, like a rock in the road, or bottoming out in a dip. Either scenario ends with the car in a ditch or with a hole in the sump. Chatting to people who see a lot of Caterhams (Boyd of Highland Caterham Hire and the fine folks of Dreadnought garage) they see a lot of sump damage. Boyd has just fitted protective plates to his cars, and Dreadnought talk about it as a fairly common issue. This convinced me I’m not worrying over nothing.

I’ve spoken to Caterham about the ride height and it’s not a fault in the car or the way I have put it together, more a combination of 13″ wheels (which I chose for handling and looks), street suspension on the 360S pack having no adjustment, and the wet sump on the Duratec in the 360.  Having discussed the options with Caterham, if I fitted the adjustable platforms on the dampers I’d have the same set-up  as if I had the adjustable suspension specified from the start. I’d also be able to raise the ride height and save my worries. I decided to buy and fit the kit, plus it gave me an excellent excuse to get out and work on the car again.

I ordered up the kit and it arrived within a couple of days. If you do the same, do check with Caterham that you have the dampers that will work with the kit – you need to be able to see grooves in the circumference of the damper body. The kit comes just as you see in the photo on the Caterham Parts website. No instructions, no guides, just four sleeves and eight rings.

The dampers without the kit

The stock suspension assembly comes as a unit, with the spring under tension between two fixed platforms. The platforms are held by a ring at the top of the damper, beneath the eyelet, and a circlip around the damper body. Unbelievably, the small protrusion of the circlip from the body of the damper is enough to hold the weight of the car across the four corners.

The dampers with the kit

With the kit, there is a choice of position of the cirlip holding the bottom platform. The front dampers have three potential positions, and the rears have two. I elected to put the fronts on the second groove, copying those I saw on a visit to the showroom in the summer, but also giving me about 2 – 3 cm of thread available to lift the lower platform. The other options I judged to be too high or low, outside of what I would consider the normal range of compression of the spring.

Fitting the kit

Fitting the kit is pretty straightforward. As always with Caterham though, there are some difficulties to overcome along the way.

The steps I took are as follows:

  • Take the damper off the car;
  • Compress the spring;
  • Free off the top platform by sliding it out via the slot cut in it;
  • Lift the compressed spring and the bottom platform off the damper;
  • Move the circlip;
  • Unscrew the top eyelet and remove top retaining plate;
  • Apply plenty of grease and Coppaslip and drop the collar on to the circlip;
  • Screw the adjustable platforms onto the collar;
  • Re-attach the top eyelet;
  • Replace the still-compressed spring;
  • Replace the top platform;
  • Uncompress the spring;
  • Refit the damper.

Nothing too hard, right?

Compressing the front springs

I started by getting the car back up on axle stands and removing the four dampers from the car (that bloody top bolt at the front was not nearly as troublesome this time around).  Compressing the front springs was a bit of a challenge. In preparation, and ignorance, I bought standard spring compressors, suitable for a “normal” family car. They are way too big and I could not get the hooks correctly located on the springs to get purchase. Switching to motorcycle spring compressors worked a treat. These have much smaller hooks and just the right size for the spring. The key to getting the spring compressed was  balance – an even number of turns for each compressor arranged on opposite sides of the spring. Slow and steady wins here – there is a fair amount of energy stored in the springs when compressed which made me cautious, and I did have a couple of minor slips of the compressors when I got the balance wrong.

Removing the spring and fitting the collar

Once I had the spring under tension, the top cap slipped over the damper rod via the slot cut in it and the spring lifted off. The bottom platform also lifted off easily, revealing the circlip.

Feeling like I was making great progress, I dug out one of the collars from the kit and tried it for size. Well, I would have, only the collar is sized to the damper body and won’t go over the top eyelet. A quick enquiry to the Caterham Parts guys confirmed I had the right kit, but would need to unscrew the eyelet. So with a spanner on the SV damper extension bar and a big Allen key in the eyelet, it twisted off reasonably easily after I broke the Loctite’s grip on the thread. Finally, there is the locking nut and the hex extension bar to undo in order to get the top retaining plate that the top platform rests against off the damper bar.

On with the collar and a quick check of where the lower platform sits with the circlip in it’s starting position, and it’s too high. I lifted it out of it’s groove with my circlip pliers and I scooted it down the body of the damper to the next slot. This gives me a bottom position just slightly lower than pre-kit and a good 4 – 5 cm of height adjustment upwards. Spot on. I then put a thin film of grease under the collar and slathered the thread in Coppaslip – what a difference this made to the smooth running of the thread.

Reassembly was the reversal of the steps above. Eyelet on, spring on, top cap on, release the spring gradually and check it seats well. One down. Repeat for the second front and suddenly I’m half-way through the job.

Rear dampers

The rears are much the same in principle to the fronts. The springs are different: longer, more stiff and variable-rate, with the top third being more closely coiled than the bottom two-thirds. There is no handy hex extension bar either, so a different approach is required for the eyelet removal.

Many thanks Brian.

Brian, the garage owner, adjusting the location of the head of the compressor to fit the damper assembly

First, the springs. I tried both sets of compressors to no avail – the motorcycle compressors were’t powerful enough to deal with the 3″ spring without worrying my greatly and I could not cook up a scheme where I could compress the spring safely. After puzzling for quite a while, I ended up touring local motor factors and garages asking whether they had anything that would do the job. Nobody did, so I called Dreadnought who quickly confirmed they could sort the springs for me. When I turned up at the garage the owner dug out an old contraption buried at the back of the work shop which was designed for compressing TVR springs. The entire thing consisted of a big lever with a hole in the top just big enough to pass over the end cap but small enough to catch the spring top.

Once the springs were off, the top eyelets proved more difficult than the fronts. Again, the skills of the owner of the garage came into play and a quick blast with a small blowtorch warmed up the Loctite enough to free it off.

Another 5 minutes later and both were done and all re-assembled. Many thanks to Dreadnought for helping me out, otherwise I fear I would still be puzzling over the process now. Next up is the adjusting of the ride height and a check of the alignment before the good weather comes.