Timm's E31, E32 and E38 Differential Oil Change
Stopping Groaning Noises on Limited-Slip Differentials
I had the offer of a 3.15 limited slip differential for a good price and had it fitted at the end of 2013 - it is a brilliant way to increase acceleration and road-holding. The only downside was that there was a noticeable groaning from the diff at slow speed when turning tight corners.
I had heard of this problem in the past, and heard it can be cured by the introduction of special friction-modifiers such as with LubeGard's Limited Slip additive. Well, adding the friction modifier worked for a while (probably 3 months or so) and then the groaning came back, so I thought I would do an oil-change to remove the Lubegard and stick some decent oil back in - some Castrol Syntrax Limited Slip 75W - 140, you will need 2 Litres:
So, no messing about, car up on ramps:
Here's the drain and fill plugs:
Both plugs are a female 14mm hex, there's just about enough room to get the tools in there. Always start by removing the FILL plug, it would be unfortunate if you drain the diff and then find that you can't refill it:
Get your oil tray under the differential and remove the FILL plug as shown below:
Then remove the DRAIN plug and let the oil drain away for 10 minutes or so, it's pretty viscous stuff and takes a while
After 10 minutes, refit the drain plug using a new washer - a slight heave on the wrench shown above (20Nm) is enough
Unless you have a fluid transfer pump, getting the oil in the diff is going to be awkward even with the extendable neck as shown above. I reckon I got about 700mL from each bottle. To get the rest in, first transfer the remaining 300mL in to the other bottle and squeeze as much into the diff as possible. For the rest I have a large syringe with a pipe long enough to reach the bottom of the bottle (once the neck is removed). It's not as easy as it might seem as the oil is like golden syrup and you will get the shakes pulling the end of the syringe out (I did)!
As usual, I made a bit of a pigs-ear of it when, prostrate under the car, I pulled the syringe a little too far and the end popped out splatting oil over my jacket, the inspection torch and my face - the oil stinks and you will not be free of the smell for at least a week.
Once you have got close to 2 Litres in the diff, the oil will start coming out of the fill plug. Refit the fill plug (20Nm) with a new washer. Decant the old oil back into the bottles for the correct disposal method and you are done. This is my second oil change with Syntrax and there is no return of the groaning. The old oil that came out (10,000 miles since the last change) wasn't too bad at all, I could have left it for another 10,000 miles. This time, as well as squirting oil over my face, it is also pouring with rain - but, it is quite dry under the car!
I've also got a better oil tray - with a spout - that makes getting the oil back into the bottle so much easier. One week later my jacket still stinks.
All done, time for a cup of tea