(This one of several tech topics originally written for the RS Register by Adrian Palmer)
Several new RS owners have experienced some concern over the noises that the RS can make in neutral and when pulling away. There are a number of gearbox differences between the RS and the standard C2:
- The ratios of first and second gear are revised (longer).
- The box uses steel synchro rings for the first 4 gears.
- The RS is fitted with a Limited Slip differential which has a 20% lock under acceleration and 100% in deceleration.
- The gear linkage has modified shift sleeves (to enable quicker shifting).
- Gear linkage is revised with reduced travel and increased height.
The ‘coffee grinder’ chatter when pulling away is down to the LSD and is quite normal. Incidentally you can reduce this chatter with a different grade of oil, but this will to some extent affect the performance of your LSD (It will not damage it in any way but you can reduce the friction marginally and quieten it down a little).
There is nothing special about the factory fitted oil, it is not synthetic or even semi-synthetic. I have experimented with different oils in the diff and settled on a combination of two grades of redline synthetic gearbox oil. Redline transmission oils are very high quality products which are a little more expensive than standard oil but are significantly better in terms of protection, power loss and noise!
I recommend using 50% lightweight shock proof and 50% heavy weight shock proof. These products are available from motorsport specialists, the cost is around £50 or so). I am not sure about the cost of draining and refilling with new oil but it won’t be too expensive. Changing the gearbox oil is often overlooked and is a really good way of giving your RS an extra little bit of protection for those hard track days. For those who have crunched the odd gear in the past you will also have the opportunity to have the magnetic drain plug and old oil inspected to see just how much debris is in there!
The other noise common to the RS is the chatter at idle, again quite normal. This chatter should go away when the clutch is pressed and is down to the idle bearing and gear lineage assembly. This is one of the real clues to the pedigree of the RS and it is the exact same gearshift as used in the Carrera cup cars and the majority of race cars. In fact I am told that it sounds exactly the same inside a Porsche 962!
Once you have driven a 964 RS and then go for a drive in a more comfortable road orientated 911 you hanker after those little reminders that the 911 is a race bred sports car and needs a few small quirks to endear itself to you as something a bit special.
So next time you are sat in traffic and the gearbox is grumbling away reassure yourself that you are in the seat of a true race car, listening to the same noises as Derek Bell has for years at the start line of Le Mans.