Hi,
I’m looking to get a mk2.5 and really wanted an LSD on mine. I found a decent car that’s an 05 Icon. I’m not sure but it seems like these probably didn’t come with LSDs as standard? Either way, I wanted to find out without actually getting the rear axle up on stands. What are the physical differences between the open and LSD diff? I read somewhere that the LSD has those cooling fins on it, but then when I looked for the part itself that were up for sale, some of the open diffs also had fins so it’s not very clear.
There’s no way of telling visually AFAIK.
I think that’s right: no external differences. Probably the least dismantling option is to remove the filler plug and try to peek in, and you might just glimpse identifiable parts if you know what to expect.
No mention of an LSD for either 1840cc or 1600cc. for model year 2005.
http://www.mx5-mazda.co.uk/icon2.htm
Earlier Ltd Ed one / ones did it appears.
http://www.mx5-mazda.co.uk/icon.htm.
Which…perhaps has added some confusion in the past.
Frankly you’d be better off without the post 2002 LSD. Later ones gave bother loosing internal tabs. More potential trouble than really worth it.
I’ve got an 05 2.5 Icon which originally had a Fuji LSD fitted as standard. Unfortunately the friction plates started to break off and graunch around inside. Changed it to a Torsen 4:1 LSD and all is good. 
I guess the only way you knew that because it was listed as an option they took?
Original buyers could never “option” an LSD, as a general rule, Sport models had them plus the odd special edition. I believe, the LSD goes hand in hand with “big brakes”, so in theory, if it’s got “big brakes” it’s got an LSD.
I have the LSD on my 2003 Sport. What should I be noticing different compared to a regular non LS Diff?
I’d assume the only benefit is if driven “properly”, as opposed to the way I drive it (ie gently)
I had a second hand LSD fitted to my 2.5, it helps on slippery surfaces. Surely you could find out if one is fitted by driving on a field or jack up the back axle and run it in gear, trying to hold one wheel. All precautions to avoid the effects of gravity being in place before attempting this.
Yes, I had forgotten: there is a way for the PO to check if an '05 car has an LSD without opening anything up, but it involves jacking up one back wheel (and chocking the other as it needs the handbrake off and the car out of gear).
Since an '05 Mk2.5 will have a Tojiki-Fuji Superdifferential type LSD rather than a torsen type, you can check if it’s easy or very hard to turn the jacked up wheel. Fuji’s have springs applying significant preload which makes the axles very hard to turn by hand if both wheels can’t turn together. An open diff will barely resist at all. (A '94-'03 torsen would also barely offer any resistance due to the different way they work, so this test is no good for spotting those.)
1 Like
Easiest way to check the diff is to jack the whole of the rear up and spin one wheel.
If the other wheel spins the opposite way its an open diff.
If the other wheel goes the same way its an LSD, unless the car has been raced and has a welded diff.
No, that test isn’t reliable and different types of LSD behave differently. A torsen LSD will happily let both wheels go opposite ways. A Fuji will not.
@Martin_Young
Interesting. An MX5 specialist has previously told me that my 2001 1.8 Sport has a 3.6 Super Fuji LSD so I tried your test (chocked, out of gear, handbrake off) and the jacked up wheel turned freely. From what you are saying I cannot have a Fuji LSD, so I was misinformed. Either I have no LSD or a Torsen LSD, but I am assuming the latter to be the case.
Assuming I have a Torsen LSD can the MoT inspector test the brakes on his roller set-up without damaging the LSD?
They didn’t fit Fuji diffs till about 2003 so far as I know. A 2001 car with an LSD ought to have a type 2 torsen.
1 Like
So is a Type 2 Torsen MoT roller proof?
I think the MOT rollers was the reason my old Fuji diff broke down. I do not let my torsen be put on the rolling road.
1 Like
So far as I know, torsens don’t have the same problems with brake testing rollers that Fuji’s seem to have. I can’t say for sure, but note that diff failures blamed on MOT brake testing wasn’t a thing I saw discussed until they started testing cars with Fuji diffs. By that point, cars with torsen diffs had been taking MOTs for about 10 years.
1 Like