small case > large case diff

[CraigG]

ive got a 318is, which has a small case4.10 diff in it, i think

is a large case 3.91 lsd a straight swap for mine? i know acceleration will suffer, but tbh, there aint much difference between a 3.91 and a 4.10 imo. i guess ill find out when i fit it, eh?

is the final drive dictated by the diff, or the gearbox? if im changing ratios of diff will i have to change the gearbox aswell?

is there any way to tell if a diff is a LSD or open diff just by looking at them (ie in a scrappy?)

cheers
craig

[Jhonno]

both dicated final gearing, box will be fine

lsd has a S before the ratio on the tag, or if you turn one output the other will turn in the same direction

diff is larger, have to shorted the prop slightly by sliding it up its splines..

[CraigG]

cool, is shortening the prop a case of pushing it, or you gotta faff about with clamps etc?

[Jhonno]

loosen the collar and tap rear (gently)

[Jhonno]

the retighten of course

[Brianmoooore]

the retighten of course

And then apply the correct preload to the diff.

[Jhonno]

what is the correct preload? im sure i read its a 5mm gap or summat

[fowler]

about that just donr this i left 7mm

[CraigG]

preload? i think youve went right ahead and lost me on that one.....? whats that about? :S

[Andyboy]

Just slacken the centre collar (just behind the centre bearing) and tap the back of the prop in slightly. Fit the big casing diff (straight swap) and tap the prop so that it sits up against the diff flange. Tighten everything up and the job's a good'un. I've done this twice and it works.
A 3.91 woun't even be noticeable on a 318iS. A 3.64 would be obvious though!