Mechanical layout of the NC MX5. The "ladder frame" was removed and not fitted to my Clubman, however it needed to be replaced with new mounts which are detailed in these pages.

The original design and construction by Mazda. Too good to mess with and easily installed and removed as a unit. The subfram itself is surprisingly light and a credit to the Mazda engineers.

The complete NC Mazda MX5 rear end as removed from the donor vehicle. In this photo the front of the diff housing is supported on timber as it is no longer attached to the "ladder frame" which supported it in the orginal vehicle. The actual subframe is not as heavy as it looks, in fact once it was stripped bare for painting I was surprised just how light it really was. And it's easy to remove in one piece by undoing just 6 main bolts.

Mazda's well engineered 5 link rear suspension. The MX5 subframe was installed as a unit into the Locost, rather than do away with the subframe as some other builders have. I could not justify the extra work required to design and fabricate mounts on the chassis to do away with the subframe. Strength and accuracy in placing the mounts would be an issue and once the mounts were installed and the chassis strengthened I doubt there would be a noticeable weight saving.

The start. The subframe was stripped of the suspension and placed in the correct position on the build table and then the rear of the chassis was built around it to pick up the Mazda mounting points.

The full MX5 rear subframe was reasonably easy to fit. Further bracing was added later and here you can see the three main mounting bolts on the left side.

The MX5 subframe itself also added a lot of strength and rigidity to the chassis. No rubber bushes were used as sound and vibration issues were not a concern in the Locost.

And here we have the subframe mounted in place and ready for everything to be built around it.

A small amount was cut off the subframe ends to make it more compact. The open ends were closed off by welding steel plates in place. A crush tube has been welded into the square chassis tube for the mounting bolt and the section was later reinforced with a steel plate.

It was a matter of trial and error to devise the best mounting position for the subframe as I had no plans to follow.

The six main mounting points fabricated and a few minor modifications made to the MX5 subframe.

My MX5 donor car was an auto with a 4.1:1 standard diff. No Limited Slip Differential (LSD) was available for the auto in Australia. The manual MX5 did have a LSD but it was a higher ratio. I wanted to retain the ratio but add a LSD as the lightweight Locost could be subject to wheelspin. So I bought a LSD from an importer of MX5 parts from Japan where their domestic market had a 4.1:1 LSD. I found only a slight difference in the mounting bracket between the original and LSD. The original diff (left) has AT (Auto Trans) and the LSD has MT (Manual Trans). Both diffs are the same on the outside and the LSD bolted into the auto bracket and subframe with no problems.

LSD with the auto drive shafts which simply push into place. A very easy design to work with and the manual and auto shafts are interchangeable.

I test drove the Locost before dismantling it to paint the chassis and noticed that the diff mounting bushes were rather soft and allowed a lot of movement. This was OK in the original MX5 which needed to be insulated from noise etc, but in the Locost there are tighter clearances and excess movement of the diff is not desirable. A set of stiffer replacement polyurethane bushes from Super-Pro provided the solution.

The Super-Pro polyurethane bushes were a quick and easy fit. Being a lot harder than the original, they greatly reduced the unwanted movement in the diff mounting.

The original MX5 subframe appears rather heavy at first glance, but stripped to the bare bone like this it's surprisingly light. Mazda engineers were very aware of the weght restrictions in designing the new NC model and weight was saved wherever possible.

Rear suspension parts received a bit of TLC and a coat of two pack paint.

With the original MX5 ladder frame removed from between the auto and the diff, a new method of supporting the front of the diff was required. My solution was to use the original mounting points on the diff housing and fabricate my own brackets which would then attach to the subframe to allow the diff to be part of the subframe to simplify installation and removal.

The two brackets still allow the diff to move. Owners of other Locosts that use the earlier MX5 diff informed me that this mounting point is critical. It's under a lot of stress and some builders have actually broken the diff housing. Hopefully my solution for mounting the front of the diff is strong and flexible enough to withstand the punishment of spirited driving. Only time will tell.

Fabricated brackets bolted to the front of the diff housing.

The brackets are designed to still allow some restricted movement of diff assembly.

Fabricated bracket added to subframe to support front of diff. Vertical extension bolts to chassis. Not visible in these photos is the additional reinforcement welded to the inside of the subframe.

And this is how it all comes together with the front of the diff held in place.

Another view of the custom fabricated diff mount.

The top mount has a supporting bracket that bolts to the chassis for even more strength.

All bolted in place. Brackets and bolt can be accessed while the subframe is in the vehicle.

View of the left suspension in place.

The subframe has six main mounting bolts holding it in place.

All finished and awaiting testing to see if all the theory and hard work were worthwhile

The rear GAZ shock absorbers were rubber bushed top and bottom, however, after a few thousand kilometres on the road the top bushings were showing signs of wear, probably due to the angle they were mounted at. So the top bushes were replaced with rod ends which was a factory option.

Closer view of the GAZ rear shocks. The top one has already been changed to a rod end and the lower one has the original rubber bush still in place. The ends are screwed onto the shafts for easy replacement.