A Frame - Failure

Quick summary:

The A Frame bent whilst on a track day when I wasn't really pushing it that hard, the damage to the A Frame has caused movement in the driveshaft which has caused the CV tripode to also break within one of the drive shafts.

Caterham have been excellent once again, whilst they acknowledge that these parts are a wear and tear item, they have also said that this shouldn't have happened to the car after 3200 miles and a few track days, as such they have sent me a replacement A Frame and Drive Shaft as part of the warranty.

Caterham were told about this issue Tue 23th Sept, and it has been resolved today Friday 26th Sept, still pending a parts delivery, I couldn't have asked for more from them really.

So on with what happened, with only 3100 miles on the clock whilst taking part in a track day, the car suffered a pretty major "A Frame" failure. A few of us spent quite some time working out why or how this could have happened but the general conclusion is that the actual part must have been weakened or faulty from the start.

The actual time where the frame bent and buckled was on this corner at Bedford Autodrome:

It felt like the movement of the De Dion bar after the bend of the A Frame must have made the drive shafts disengage for a split second somewhere (hence the revving of the car), I quickly let off the gas and clutched in to let it settle, and tried not to stress the car laterally whilst hobbling back to the pits.

Once back to the pits, it was clear that the A Frame had bent, and it was day done, luckily it was the last session on the track.

A quick inspection at home revealed that not only will I have to fix the A Frame, but I also had a pierced CV boot, which was annoying as this would need to be fixed as well.

Given what had happened, I decided that I would basically strip the car down at the back, clean it up, check all the splines, chassis, mounting points etc. The De Dion must have moved quite a bit when it failed so this was the sensible thing to do.

Once it was stripped, I couldn't see any damage to the chassis, the radius arms were all in place and secure as expected, as were the shocks. The De Dion is basically left hanging from the shocks, which do actually allow for lateral movement of the bar, as such it would be unlikely that the shock mounting points under the roll bar would be compromised. The radius arms are bolted "through" the chassis from inside the cabin, again this is good news because this means the chassis is unlikely to have suffered any stress at a mount point here as they are not "fixed" to the chassis. So I think this is all good news and probably entirely why the car has it's mounting points setup like this.

Next up, I inspected the drive shaft spline, and these all looked in good condition, other than the punctured CV boot. The only part I couldn't inspect was inside the differential, but I'd expect the splines to have burred at the end if anything was to happen and the diff left untouched. I've stripped the punctured boot and inside was not great news, I've now found that one of the CV joint tripodes is broken so I will need a new tripode at least too.

If you look at the grease inside the boot, you can see all the bearing needles mixed in with the grease, I believe this, and the stress of driveshaft stretching when the A Frame bent, is the cause of the punctured boot. If you look at the metal flange that the joint fits in, you can also see that the ends are burred, and this will explain why it was a little tough to release the CV joint from the metal casing.

Since finding this out, I phoned the Caterham parts department to see if I can get a tripode to tide me over however they do not sell the tripode (UJ) separately and advised that the usual replacement for this would be a whole new driveshaft. this is the SV RH BMW Diff shaft with the speed sensor - part 500A0004A. A friend of mine has a broken shaft which I'm going to try and get the tripode off and use to get the car up and running for now, hopefully it will just slide onto the existing shaft. At least then I'll have a car that I can use until CC get back to me formally with their take.

Inspection of the damaged A Frame

Inspection of the splines