We’ve always complained about our diff… We don’t it mid corner so much, but as you try to get that power down, the inside wheel often spins up (see this hot lap for example, listen to the RPM out of the tighter corners). Luckily though, it’s a viscous LSD, so with not too much work, and very little expense you can replace or add ‘shims’ to one or both sides of the LSD inside the diff. This essentially adds pre-load or tension to the diff, tightening it up and requiring more torque difference across the axles before it will slip. It’s not a fixed ratio it’s just a particular load.

So after forking out for a few different shim sizes at about $9 each from Nissan, we pulled the diff out, split it and … oh dear; Much like the fuel pump we went to upgrade, we found that someone had been here before! It already had a 1.45mm shim in there. The nearest larger size to this that you can buy is a 1.49mm shim, so we assumed this is what was installed and it had worn down to 1.45mm. This threw our calculations out a little. Regardless, we still needed more tension and without opening the LSD further to get to the shim on the spider gear side, we assumed this was still stock at 0.8mm giving us a total preload from the shims of 2.25mm (Stock should be 1.6mm). So we replaced the 1.45mm shim with a 1.1mm and a 1.2mm giving us a total of 3.1mm (almost double the stock preload). The risk here is if we go too far then we will have a diff that locks too easily. This would give us a lot of oversteer on exit as we try to get the power down. Given that the mechanics of this don’t car about the direction of the torque, over ‘tightening’ the LSD could also lead to lift-off oversteer. Something we were already getting too much of in the wet last track day.

But, only one way to find out, so we trusted our research and bolted it all back together and hoped for the best!

Whilst we were covered in diff oil, we forgot to take any pictures at all, so here’s a few snaps that someone else took doing the same job:

http://www.skylinesaustralia.com/forums/topic/164288-diydiff-shimming-for-r33-gtst/