Big update time, only because I've being slacking with updates here:
The judder I was experiencing on up-changes in S6 in the 7000-8000rpm range, was definitely not wheelspin, jury is still out if it was wheel hop or not but I never experienced it on the stock heavier wheels with 255/40/18 and it only started on recent trackday at Anglesey. Never had an issue on previous track days, but they were admittedly warmer and I had tyres that still had rubber and were not hard plastic.
However the cups which gave me zero confidence and very little grip due to going through far to many heat cycles were also pretty knackered:
OOOOOOOOOOOOOOOOOOOPS!!
This judder I was still experiencing but I tried a clutch re-set using DIS/GT3 instead of INPA which made the gear changes rather lazy and subdued and caused slur, but after a few runs in S6 the judder seem to go away. So I am thinking maybe the last track day hot spotted the clutch or flywheel and the judder was coming from the clutch and being transmitted down the propshaft into the diff and hence the rear judder sensation. The cars clutch slur is all but gone now in S6 and the changes are going back to their usual firm but also car friendly and simply feel efficient yet firm.
After the reset I drove it around in S3 in full attack which incurred quite a bit of slur but suspect it was needed to burn any rubbish of the friction plate surfaces, I shall see how I go along and if it returns I shall refit the stock wheels to try and rule out wheel hop.
The car had a full inspection today, no lose bolts, nothing broken and the differential is very tight with only a very small amount of up and down play on the drivers side which is how the M differential should be, so all is well.
Whilst it was in the garage I had the front suspension refreshed, well new track rod ends as I've never done them in my ownership and as ECP had a great deal on Lemforder it made sense, I did lollipop bushes some months ago so now the front of the car is all brand new except the main front arms but they show no signs of wear/play. I also replaced both upper and lower steering column as at 100k miles I would expect some play, my car had no play but the steering wheel did not feel as tight as it could be.
New parts:
The old track rod ends that came out actually seemed fine, no play and the boots fine so shall keep as spare or sell. The steering column also had no play but the new parts had far higher resistance to the movement and after now driving the car the steering feels better for sure, a lot more positive on the straight ahead and feels better weighted, so a good shout to the people who mentioned it is worth doing. The Mechanic had the lower part done in like 20 minutes, the upper part took about an hour as was real fiddly but in short you can probably get away with just the lower part and as it cost so little from BMW it is well worth doing if your steering has play or feels very numb and light.
I also had the car aligned, the thrust angle in the rear was not straight ahead, only 3 minutes and camber was 30 minutes greater on one side, maybe these could have being contributing to the judder if the differential was getting upset by it though I feel my hunch on it being the clutch hot spotting is most likely more accurate.
With the new tyres, complete new suspension throughout the car and all bushes/mounts refreshed it feels bloody awesome to drive, so tight and the new tyres are nothing but impressive.
I also dropped the spare diff of with the powder coaters today to get it blasted and painted in a silly colour.
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Then end of week I hope to drop it of with diff builder who shall put the 3.91 final ratio in which is REM treated which helps reduce transmission losses and noise along with a complete bearing/seal refresh. They will also check the LSD plates at same time and comment on lifespan, fingers crossed. I shall also get them to install the differential, I shall then post the ECU off for CSL conversion and I can finally flash Frank's TTFS tune to the car and enjoy how it is drive on map sensor along with a 3.91 ratio in the car. I cannot wait!
One question, will there be a running in period for the diff, if so does anyone know what it shall be and of course I shall ask the guys building it for their advice to.
