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I would like to change the diff ratio of my track-only 2006 NC from 3.7 to 4.1. I am pretty handy on the tools but as a MX5 newby I would appreciate any advice about tips and traps or a link to a post on the procedure.
So far I have done some 1200 track km in the last 11 months and the car has displayed an enviable reliability record apart from the usual need to upgrade a worn front hub.

got access to a hoist??? That makes this job pretty painless

Ive done a few diff installs on the NC now

Mark the alignment bolts before removing them. People say to just pull the driveshaft out at the hub, I pull all the suspension arms off with the hub itself.

Mark the alignement of the PPF bolts off the gearbox before removing the PPF

Apart from that its a pretty easy job, with 2 people you can knock it over in about 2.5hrs, also depending on the Kms on the car, the diff mounts may be stuffed.

Tick to everything Reggie says. He did mine.

The circular rubber mounts inside the diff hanger of a 2006 will probably be broken. Get the OEM rubber replacements as the neoprene ones transmit a lot of noise and vibration.

I sourced a crown wheel and pinion from an auto diff and had DiffTechnics set it up. Worked out cheaper than getting a complete unit.

If you track only, then I'd look into upgrading the LSD at the same time.

Resurrecting this thread since I'm thinking of doing a 4.1 swap at the moment.

Does anyone know if it's possible to buy a full auto Diff assembly with the 4.1 FGR in it, put an aftermarket LSD in it and use that? I was thinking it would reduce downtime and would leave my original Diff untouched so I could sell that off after the new one is in.

Dan wrote:Resurrecting this thread since I'm thinking of doing a 4.1 swap at the moment.

Does anyone know if it's possible to buy a full auto Diff assembly with the 4.1 FGR in it, put an aftermarket LSD in it and use that? I was thinking it would reduce downtime and would leave my original Diff untouched so I could sell that off after the new one is in.

Yep that will work. Aftermarket LSD centres aren't cheap though. You are looking at $1300+ Just for a LSD centre.

The stock LSD is more than fine. Phil is doing 1.09's on the std LSD with the 4.1

I got a 4.1 ring and pinion from the big forum (think it came from Greece) and got it installed.

Better off doing that and putting the money towards headers and exhaust

As always thanks for the great advice!

You make a good point that I probably don’t really NEED an LSD, on the surface it seems like a ‘why the f&@k not’ mod while the diff is apart but costs add up though since I'll need the Diff, 2 bearings, 2 oil seals plus possibly shims depending on how it fits.

Good to know that the Auto Diff is the same though minus the LSD since that opens up options. I'll give my mechanic a call and have a chat about what he thinks before I go buy something and he calls me an idiot.

Dan, I used a second hand crown wheel and pinion out of an auto diff ($300) and had them installed, lash set and new seals into the diff by Diff Technics at Kogarah for $384. I didn't need new bearings.

I'd suggest you give them a ring because they do have a lot of parts and different ratios there that may be as cheap as sourcing parts from an auto diff.
They also can source all aftermarket LSD centres.

I had mine back in a few days even after I told them I was in no hurry and a week or two would be fine.

Regie wrote: The stock LSD is more than fine. Phil is doing 1.09's on the std LSD with the 4.1

The 1:09 was with the 3.6 diff. I'm yet to unleash the 4.1 at Wakefield.

Thanks for that CB.

I've managed to source a full JDM Diff at a good prive so it looks like I'm going down that route, should have it in next week.

By chance do you have a part number for the rubber mounts you replaced?

Dan wrote:By chance do you have a part number for the rubber mounts you replaced?

Sorry, I replaced the complete hanger with a second hand unit, many thanks to Daniel.

Cool, Daniel is the one I'm buying it off so I'll make sure he does it many thanks to that guy indeed, he's got me out of a couple of binds.

My Diff actually has a rattle at low revs with anything more than a light load (it sounds like a mount and not mechanical) so it'll be good to get rid of that.

There is an LSD here. http://www.gumtree.com.au/s-seller/Raenier/1005336999
Greg.

taminga16 wrote:There is an LSD here. http://www.gumtree.com.au/s-seller/Raenier/1005336999
Greg.

It's a 3.6 not a 4.1, so there won’t be much interest.
It may be interesting to see who’s the first to try an LSD in an auto given that the ECU controls the wheel spin in the auto.
We were down at Phillip Island a couple of years ago and Roger in his auto NC wore out a set of rear pads in just one day. Not nice driving back to Sydney the next day with no rear pads.