I ran the car for a very long time with the standard back axle – all standard components. In this setup and with driving the 1400 hard, it would appear that the halfshafts only lasted about 15,000 miles before needing to be replaced due to twisting up.
A track day at Croft burst the rear oil seal and caused the diff oil to come out all over the brakes. This destroyed a crownwheel on the diff – by the time you can hear diff whine at 100mph through a helmet, the diff is toast. Inspection of the failure showed impressive witness marks on a variety of components. The hub had been catching on the brake cylinder, the drum catching on the back plate, the bearings were toast (22 miles, some kind of record?!) and the inner bearing on the diff was also toast, as was the crownwheel. A massive case of hub flex causing the seal to simply not run on the land was diagnosed.
Starting to suspect that wide tyres and track days were proving too much for the standard rear end, I put a set of double hub bearings (Frontline), speedisleeves (Simply Bearings), stronger half shafts (Magic Midget) and a Limited Slip Differential (LSD) (also Magic Midget). The first track day at Anglesey, with sticky track tyres thrown into the mix now, caused a failure of one of the oil seals on the double bearing hubs (one of 4 rear bearing failures from 7 K-midgets on track that day), which was replaced free by Frontline, but had ruined another crownwheel. The LSD had arrived after the track day, so that has been rebuilt into a 4.2 ratio differential housing with a non-whiny crown wheel.
This has made the car much much quicker. It’s about 10 mins in each hour faster cross country. It does 0-60 in 5.6 seconds. The LSD is a plate type, and when first fitted was very intrusive, causing the car to push on massively in the corners on power while cutting in alarmingly when letting off the power. The LSD has worn in a bit now, and I’ve learned a different style of cornering; there’s a bucketload of extra mid corner traction so powering put of corners results in all go rather than spinning the rear wheel. If it does spin a wheel, it tends to spin both, so needs a bit more care, but overall it’s got so much more traction. I’ve not tried a track day in it yet, but watch this space.
Rob's Midget 