As my car ends its warranty period, I thought it was important to reflect on the real-world Caterham kit-builder experience. This sequence of events happened over the 18 months since IVA and PBC. Caterham at all stages have been fantastic and have investigated my problems, if I have requested.

After PBC, I was still experiencing a couple of issues which I felt shouldn’t be present, specifically driveline vibration and noise.

Initially I thought (as did the Caterham staff during PBC), that the drive line noise was the sintered plates of the LSD, and that was to be expected. I therefore wasn’t concerned about the noise. However, even after the tyre was replaced during PBC, I could still feel a vibration in the drivers seat at certain road speeds (60 – 70mph).

During the first winter after the PBC, I decided to try and trace the cause and resolve it before the start of the new season.

The obvious candidates for vibration at speed are the wheels and tyres, even though they had been balanced and checked a few times. I decided to track down the services of a “Road Force” balancer. The good news was: my wheels and tyres were perfect. The bad news was: this meant the vibration problems lay elsewhere.

Years ago, my Sigma 150 made a horrendous clonking noise and vibration while out on a drive. The problem turned out to be a snapped spring in the driveshaft. The noise sounded like something fundamental had broken in the diff. So I decided to check the driveshafts.

On the left hand side driveshaft and wheel bearing it was obvious there was evidence of bearing fretting. Research indicated, this was caused by vibration, and this was possibly caused by undersized components. I suspected this damage was a result of the defect tyre which of course had been changed under warranty earlier. The driveshaft and bearing were replaced by CC under warranty, after a considerable delay for parts supply. Unfortunately, the vibration and noise remained.

At this stage, my options were becoming limited. The obvious next candidate was the prop-shaft, but there was no evidence of any balance weight loss, so it would have to be a faulty component within the prop-shaft, or it was not working at an appropriate angle.

There is no adjustment in the diff angle or the engine mounts, so a ruled out working angle problem, mainly due to the lack of space around the differential universal joint (UJ) to get any meaningful angle measurement. That was until one of this blog’s contributors Nick West sent me a picture of a spacer new to 2021 kits that fits between the gearbox and the gearbox mount.

The part isn’t officially part of my kit, but would fit any 5-speed gearbox Caterham since the introduction of the Mazda gearbox (in 2013). It was cheap enough to put it into the “what have I got to lose” category, so I ordered one.

Fitting was simple: Loosen the two bolts into the gearbox, lift the gearbox with a jack until you can see the weight being taken by the jack, the remove the gearbox bolts and mount bolts to install the spacer. The spacer alters the angle just a little bit, so I found it necessary to remove the mount completely, to ensure the bolt going into the gearbox had started without being cross threaded. Damaging the gearbox casing would have been very upsetting.

This spacer resulted in 95% reduction in the vibration, and in addition also achieved the eradication of the driveline noise you can see in this video when reversing in a straight line. Given that this was a significant improvement, and the 2021 summer had started, I decided, this would do. I even informed Caterham that I considered the matter closed.

Trackday highlighted vibration issue

Unfortunately “that will do” did not do, and the vibration became more pronounced at 120 mph on a long straight (discovered at my first track day outing). So the investigation continued. Ironically at that trackday my speedometer stopped working. What is it with me and Caterham speedometers (see Speed Sensor)?

This time it was the trigger wheel, that had decided to move on the Tripod joint. Since this is part of the driveshaft, my car was going to have a second driveshaft replacement, this time the right hand side. More worryingly the driveshaft and bearing had also suffered bearing fretting, so the wheel bearing was also replaced. Given the evidence I have I can only recommend builders use an anti fretting agent when assembling rear wheel bearings. I have not evidence if this paste will prevent the damage, but given the cost it’s worth the investment. I am also resigned to the fact that if a rear wheel bearing needs replacement when almost certainly the driveshaft will also need replacement. Not that I have ever needed to replace a rear wheel bearing.

At this stage I was out of ideas to solve the vibrations, so I started investigating the world of NVH (Noise, Vibration and Harshness) diagnosis. Tools seemed to fall into to brackets, expensive specialist equipment, or inexpensive smart phone apps. So various phone apps where tried.

At this stage, I would normally recommend the product or app I was using to get to the bottom of the intolerable vibration, but I can’t. The app constantly identified a T1 vibration at the first tyre harmonic, or T2 second tyre harmonic vibration as the main course of my cars problems. So I bought a new set of rear tyres to eradicate the indicted source of the problem.

The plan was to keep the tyres if this wasn’t the problem, after all rear tyres won’t last for ever. However, upon removing I found that the tyre bead was damaged badly. I didn’t want to get into who was responsible for the damage, the remover or the fitter. I was just excited that this had to be the cause of the vibration; after all, the app said it was tyres, and the tyre was damaged. But alas, no change, the app lied, and I was back to the drawing board.

Starting to run out of option, I decided to next check my Titan differential preload (as Differential Preload Check), and although I have lost 4 ft lb of preload over the 2000 miles my car had covered, I observed a strange behaviour. The left hand side preload was 20% different to the right hand side preload. I removed the rear brake pads to ensure I didn’t have a dragging pad, but discrepancy remained. At this stage I decided to phone Caterham, and Road and Race Transmissions (https://www.rrtransmissions.com) for advice. If the LSD had been assembled incorrectly, which was deemed very unlikely, it could cause a vibration and a difference in preload left to right. Road and Race Transmissions agreed kindly to inspect the LSD for a defect.

While the differential was out, it would have been foolish not to remove the prop shaft and have its balance checked.

Once I removed the diff, I took it to Road and Race, who checked the preload using a professional grade torque wrench. To my surprise, no difference from left to right preload was found! The difference was my digital torque wrench’s inability to read clockwise and anti clockwise torque (lesson learned).

BUT …

The before sending off the prop shaft for balance testing, I noticed that the front universal joint of the prop shaft felt very stiff (unlike the rear joint). Caterham sourced the replacement prop shaft under warranty and once reassembled … the vibration issues had finally been resolved!!

Lotus 7 Club 2021 Taffia Fish and Chip run

With the bolt marker paint barely dry on all the new bolts holding the diff, prop shaft and rear suspension, I decided to fulfil a life long Caterham ownership ambition and complete the Lotus 7 Club Taffia Fish and Chip run. For me, this meant a 700 mile round trip and the highlight of my first two years of ownership.

This vibration issue has pushed my love for this car and my Caterham ownership to the limit. At any stage, Caterham Service Department would have stepped in and taken ownership of the issue, but for me this always dilutes the “my car, I built it” feeling, so as a potential owner please don’t worry, my experience isn’t the norm. I know of two local 420R builders that have not experienced any significant issues.

I wanted to create this post partly are a precautionary tale, and partly to draw this build blog to a conclusion. I now feel my car is “built”, and more importantly I am happy with the result. I will however continue to blog workshop / service procedures on the maintenance site.