360 Grinding gear change - Synchro or something else!?

Hi guys,

1999 F1 box 360 (with later TCU) has a grind/scratch noise changing down from 4th to 3rd between 2-4k rpm. Doesn't happen when shifting down below 2k rpm and doesn't seem to happen at higher rpm's. Happens at a wider breadth of rpm's in sport mode. Never happens with any other gear only down into 3rd

Here's the weird bit... If I double tap the paddle to change from 5-3rd it Never happens. Does this mean it more of a software/set up problem rather than synchro which surely doesn't care what gear your coming from?

Oil seems to matter. If I use Redline mt90 no noise (but the diff is unhappy). If I use Eni Rotra LSX noise creeps in after a few hundred miles. Noise never happens when cold regardless of oil

Help appreciated!

 

Hi guys,

I've just swapped gearbox oil back to what I originally had. Redline MT90 and after around 15 miles the noise is completely gone. Overall the gearbox seems quieter too so it's happy.

As expected the downside is it makes the diff chatter a bit more prominent, I could probably cure this with some friction modifier but as it inhibits synchro action I'll avoid this for now.

For anyone else seeing this I'd recommend you replace the gearbox oil with MT90 and try it before more invasive actions. I say MT90 as it's working well for me but speak to your mechanic and decide what is best for you as this is a tricky topic with the 360!

All the best everyone