I want to get an LSD into my westfield, but would also like to stick with the 3.9 ratio I have at the moment.....I have a 3.6 diff with an LSD lying around, and understand that the crown wheel is interchangeable with out requiring another pinion - Great....

I really want to try and have a pop at cputting the LSD into my 3.9 Diff...Does anyone know of any useful literature that can help me - I already have the pdf document of rebuilding a granada diff but this does not mention LSD's - Also keen to understand how to set backlash / preload etc....so any help appreciated :-)...

Thanks.

Paul.

I watched an expert changing the ratio on a non lsd diff for me once, and came to the conclusion I wouldn't try it on my own

John

I was considering doing mine myself, but I think I'd get an expert to do it too.

Trying to find someone local, but failing that Road and Race Transmissions in Kent have an excellent reputation.

I just re-built my diff - and TBH it was no where near as scary as I thought it would be (the hardest part was getting the old bearings off !)
I set the back-lash by `feel` - with the diff clean and oil-free I adjusted it untill it just felt `right`.
No problems so far , and it's totally whine free .

You can buy 3.92 LSDs straight off sierras. Personally, I'd sell the 3.62 LSD and buy a 3.92 as supplied by the factory.

If you're swapping internals, you can leave the 3.92 pinion in the casing. Just unbolt the LSD bit from the 3.62 and bolt it into the internals of the 3.92 diff. I have heard that all the setting up is on the pinion and if you don't disturb it, you don't have to reset it. Could be wrong though.

There's a good guide in Practical Performance Car this month about rebuilding diffs, setting preloads etc

If it's a sierra diff, the only really tricky bit is setting the pinion fore/aft. Keep crownwheel & pinion together, you really can't mix & match 'em - but I can't see why you can't move the LSD part from one diff to the other without touching the pinion. The bearings are set by putting 44 ft lbs of preload on the castle nut things. Adjust the mesh so there's as little backlash as possible at the highest spot on the crownwheel (there's always a highest spot....)

I once changed the crown wheel and not the pinnion on my Mini, my dad a mechanic of around 40 years advised against it, so i went with my own judgment cos what does an old fella Know. Funny old thing drove 5 miles heard a massive bang car coasted to a holt. Then I rember talking to him about an hour later I think he said TOLD U So. the pinnion shattered. You live and learn. not sure whether this would be the same on a sierra

You're keeping the 3.92 crownwheel and pinion as it is, but just unbolting the open diff from the crownwheel and bolting on the LSD. Easy peasy and no need to worry about the pinion to crownwheel setup.

Liam

Thanks for replies: -

I know the pinion can be kept, which will effectively make life much easier.......So, as far as I can tell, it really is a case of removing the crown wheel from the 3.9 diff carrier, and putting it on the LSD.

Having not long finished building an engine, and converting car from Carbs to Fuel injection, I'm up for a challange :-) - So, am going to ignore warnings and have a go muself :-) - Watch this space for a 'Does any know a good Diff rebuilding company :-)

Paul.