- My model of MX-5 is: MK2.5 1.8 Euphonic
- I’m based near: newcastle
- I’m looking for technical help or recommendations on: repalcement Diff
Hi, I am looking for advice on a replacement diff for my MK2.5. The car developed a clunking noise coming from beneath and behind the drivers seat around 3 months ago. It didn’t get any worse until recently. I can now here a metallic clicking noise very often in 1st and 2nd and sometimes 3rd gear. It seems to occur more often when I apply power or lift off especially in the lower gears. I’ve previously had the diff oil changed to find a metal shard on the magnetic drain plug.
I know there are multiple diffs out there but I am not sure what’s best to fit. I don’t really want to change how it drives, but I have thought about turbocharging/supercharging down the line at some point, and I’m not sure if there would be a more recommended diff to use in this case.
The car is OTR as the rate at which the diff seems to be decaying has increased. However, I’m surprised it’s lasted the 115k miles it has accumulated over time. I’ve read on here that peeps with less than 60k have beaten me to it which is quite alarming.
Thanks
There’s a company in Northern Ireland will rebuild the Fuji diff for £125 + postage (about £15 each way). They have developed a modified spacer which they say makes the diff stronger.
See McNeill Manufacturing Engineering on Facebook, or look up MX5 diff repair on eBay.
I spoke to him last week, and he seems very down to earth and knowledgeable.
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Nice find HITW. Would definitely seem to be the way to go with this.
No diff expert but would have thought the Torsen 2, 3.6 fitted to the earlier MK2.5 was the better diff; Russ, the Fuji repairer seems to assert otherwise. Anyway these are now selling for £5-600 where a Fuji can be bought for less than £200.
I think Bofi or similar also fit new internals to the Fuji diff but from memory that takes it from 3.6 to 3.9 and not cheap.
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Thanks for the info, much appreciated.
Given the diff is damaged, that is a very good price. Do you know if the price includes the knew spacer? I wouldn’t mind a repair like this as long as I know the diff will become as durable as the Torsens. If not, I would rather pay for a Torsen replacement.
I was actually looking on Bofi Racing at the Blackline Helical diff. However, there are design floors noted on the product page so that is out of the question.
Il make contact with McNeill Manufacturing Engineering for more info.
Thanks again
Here is the Ebay link but I would definitely speak to him first. It does sound like a full repair and case refit with just delivery both ways to add to the £125 or best offer:-)
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@ Lewis I think that’s the all in price to fix the cone clutches and spacer. It doesn’t include bearing replacement, but they can do it if needed - normally they don’t need it, apparently. I’ve just pulled mine apart and it seems fine.
They expect you to take the diff out of the car, take the ally frame off and wash it out to make sure parcelforce aren’t upset by dripping oil.
Best thing is to call them. Took me a few attempts but he (Russell McNeill) did call me back. I expect they’re busy doing actual work.
The way I see it, if the diff lasts no better than original, it should be good for the life of the car, after the rebuild. If it’s as good as they say, then even better. The price is cheap for either of those results.
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Just a side note on the relative merits of the different diffs. Torsen diffs are good mild mannered diffs for fast road or track use, but if one wheel slips, all the torque goes the easier route.
A working Fuji diff is a locking diff, which should maintain drive with one wheel in the air. Should be a better option for hard track day or competition use, especially if you increase the pre-load from the factory setting to make it lock up sooner. Factory settings are nice and mild mannered for road use.
The Fuji diff’s relatively unloved status in the MX5 community also makes it an economically attractive option, especially if the McNeill repair and modification proves to be robust in long term use. They’re saying it’s getting competition use with some customers, and none have come back for repair, which will be a good test for it.
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Thanks for the information.
I am draining my diff tomorrow and hopefully getting it sent off sometime over weekend. I am going to go with the repair from McNeill. If what is said about reliability of the work done, Its a no brainer to me. £500 for a Torsen or 150 ish for a renewed Fuji which from what I understand, is more performant and provides a higher level of performance.
It doesnt surprise me that he gets lots of work for them. Its immense value 
I’m sending mine in the next week or so. I hope it works out for both of us. The bearings in mine seem fine, so hopefully it just needs the standard repair and some new oil.
I think mine will cost more as I think a tab may have been eaten. However I doubt it will be anywhere near the 500. Hopefully.
Do you have any advice on what to clean the diff out with? Il have to ask what parts he needs when ive taken it off as I have no real idea what i should send to him 
I’m thinking petrol or paraffin. Don’t like the idea of anything water based that could promote rust. If you do use a water degreaser, it could do with a good soaking in duck oil or WD40 afterwards, which kind of defeats the object.
I think a lot of them eat a tab or two.
I’m sending the complete diff without the wide part of the case/mounting arms, but with the ‘pig’s snout’ still attached.
Here’s what I found. Cone clutch tabs (?)
Think that’s par for the course. Was surprised to find none in my oil. Maybe the oil was changed before.
