318is 4.27 to 4.10 LSD?

[spannerrash]

Hi folks,

I decided to splash out on a 4.10 small case limited slip diff for my 318is to replace the standard open diff.

When I fitted the 4.10 I noticed that the cars peak acceleration seemed to be dulled down, it feels like it would with the open diff but if I had the car fully loaded up with passengers and luggage (other 318is owners will know what I mean).

I was fairly confident the 4.10 LSD I bought was the real deal as it is small case, definitely limited slip, and has the correct tag. Plus the seller seemed extremely genuine when I met him.
It does 60mph sitting at roughly 2500rpm in 5th which seems lower revs than I’d expected.

I've confirmed that the diff I took off the car is a 4.27 open diff (I counted the teeth). This explains why it felt a bit more rapid. Would this be a standard option for a 318is??

I’m worried that the supposed 4.10 LSD which is now on my car is in fact a different ratio all together, possibly a 3.64. But that begs the question, did they even make a 3.64 small case LSD??

Either way, I was wondering if I’d be able to move the crown wheel and pinion over from the 4.27 to the limited slip to make the ideal diff, is this a simple straight swap which would work?

Any advice would be appreciated, thanks!

[rix313]

Fitting the CWP from your 4.27 small case open diff to the internals of your '4.1' small case LSD is certainly an option. However it's not as straight forward as just swapping them sadly. The CWP will need shimming and this does require some tooling and of course the correct shims, this does cost a couple of hundred pounds. My friend Will at Rally prep (http://rallyprep.co.uk) can put a quote together for you I'm sure.

According to my gear ratio spread sheet, 60MPH in 5TH you should be at 3000RPM with a 4.1 diff and standard Getrag 240 318iS gearbox. If I change the final drive ratio to the 3.64 you mentioned above then your speed at 2500RPM in 5TH is.... 57MPH....

Might be worth your while jacking the rear of the car up; mark a point on the prop and on one of the drive shafts (a paint pen or tape or something). Turn the prop shaft (take the gearbox out of gear of course otherwise it will be a tad hard work haha), and count how many turns of the prop shaft equals how many turns of the drive shaft. From this you can work out near enough roughly which ratio you have.

[spannerrash]

Thanks for the response! It seems I have certainly ended up with 3.64 that's gutting, I didn't even know a 3.64 small case LSD existed. Or will it be that someone else has swapped this ratio in?

I'll have to get in touch and see what they say, pretty sure I got my e46 steering rack conversion kit from them.