Our video guide on everything you need to know about Differentials for the Mazda MX-5 Miata
What's a differential?
The diff of the MX-5 Miata is bolted to the rear subframe with two large nuts and rubber mounting bushes.
The drive-shaft and half shafts need to be removed to get the differential out of the car, and often the rear section of the exhaust needs to be removed to allow enough room to lower the diff.
On the later cars, there was a variety of underbody bracing which may also get in the way.
 | The diff splits the engines power out to each of the rear wheels - but in the MX-5 it also acts a brace to the gearbox connected via a beam known as the 'power plant frame' |
Physical Differences
The first MX-5 diffs that originally came with all the 1.6 litre engined cars were equipped with what is the
smaller and inferior 6" ring gear (they are know to spontaneously explode). It was actually derived from the rear of the 1988 Mazda 323GTX which has roots that date back to the late 70's.
Mazda knew they'd made a mistake with the 6" gear, so when the 1.8 litre engine arrived in late 1993, they moved to a
larger and stronger diff with a 7" ring gear - this time derived from the RX-7 of the 80's.
The differentials very similar and are interchangeable - provided the associated driveshaft and half shafts are also swapped. So a 1.6 diff needs 1.6 driveshaft and half shafts, and the 1.8 diff can be installed in any NA or NB, even a 1.6 powered car, provided the associated 1.8 driveshaft and half shafts are installed.
Note that all the 1.6 diffs came with
two piece half shafts, that being a pair of stub shafts in the diff and then half shafts to the hub with a bolted flange to join them together.
With the 1.8 diffs, while the half shafts are not the same as the 1.6, they were again two piece until sometime in 1995 at which point Mazda moved to one piece half shafts.
There were small physical differences in the 1.8 half shafts through the years with things like ABS coming along but fundamentally they should be interchangeable.
Drive shafts are generally very strong and even with high horsepower, usually something else goes first like the gearbox before a drive shaft in an MX-5 Miata will fail.
 | All MX-5 Miata diffs are interchangeable between the NA and NB provided the correct driveshafts are also swapped |
Gear Ratios - 6" ring gear
The 1990-93 1.6 rear end was offered only in a
4.30:1 ratio - that's it for the 6" ring gear size, theres no known alternative ratios that came out of the Mazda factory however the was apparently a 4.875 after market set.
The 1.6 differential is known to fail even on stock power levels.
| Model | Diff Gearset | Engine | Gearbox |
|---|
| NA6 |
4.30:1 |
1.6 litre |
5 speed |
Gear Ratios - 7" ring gear
The 1.8 cars started out in the NA from around 1994 all equipped with a
4.10:1 diff ratio and that ran on the both the Manual and Automatic gearboxes.
When the NB first came along with the 5spd gearbox, Mazda moved to a
4.30:1 ratio diff gearset in most markets. (Known
exceptions include Australia & Europe where the 5spd NB continued with the
4.10:1)
With the introduction of the NB2 face-lift (and also with the NB1 10th Anniversary Edition), Mazda opted for a
3.909:1 diff gearset to mate to the new 6speed gearbox. (Again the exception is in Australia/Europe where the 6spd NB2 was delivered with a
3.636:1)
The 1.8 differential is generally good for 400rwhp or more.
| Model | Diff Gearset | Engine | Gearbox |
|---|
| NA8 |
4.10:1 |
1.8 litre |
5 speed |
| NB1 |
4.30:1 |
1.8 litre |
5 speed |
| NB1 Aus & Europe |
4.10:1 |
1.8 litre |
5 speed |
| NB2 & 10AE |
3.909:1 |
1.8 litre |
6 speed |
| NB2 Aus & Europe |
3.636:1 |
1.8 litre |
6 speed |
Interchangeable 1.8 Gear Set Details
Along with the OEM differential gear ratios mentioned above, there are also a number of aftermarket manufactured gearsets, as well as gearsets sourced from other vehicles which all can be retrofitted into the 7" differential.
The table below outlines all those that are known, and their source.
| Gear Ratio | OEM/Aftermarket | Part Number |
|---|
| 4.10:1 |
Mazda OEM |
M068-27-110A |
| 4.30:1 |
Mazda OEM |
M061-27-110C |
| 3.909:1 |
Mazda OEM |
M037-27-110B |
| 3.636:1 |
Mazda OEM |
MA02-27-110 |
| 4.44:1 |
Mazda OEM (Not fitted to to MX-5 Miata from factory) |
M054-27-110A |
| 4.625:1 |
Kia Sportage |
|
| 4.778:1 |
Kia Sportage |
MM057-27-110 |
| 4.57:1 |
S2000 |
|
| 4.875:1 |
Aftermarket |
1312-27-110A |
| 5.125:1 |
Aftermarket |
|
| 5.38:1 |
Aftermarket |
|
Differential Centres - Open
The basic differential came as an
open centre, meaning that effectively the torque is evenly split among the two wheels, but that can result in the drive of the engine being sent to the wheel of least resistance.
The easiest way to identify an open diff, is the
shaft running through the middle of it which can be seen through the axle hole in the side of the diff.
Of course an open diff centre is the safest and
easiest to drive for an amateur, however they are not ideal for track work or performance driving as drive may be lost due to wheel-spin.
 | An open differential is easily identified by the shaft running through the middle of the centre |
Differential Centres - Viscous
There was a
Viscous LSD on offer from the factory for the 6" size differential.
They are a sealed item,
there are no clutch discs in them and you can't really service them.
There are viscous couplings within the differential attached to each driveshaft.
One series of plates is connected to each of the axle shafts. Speed difference between the axles causes the plates to rotate at a rate relative to each other.
This shear rate of a thin film of silicone enhanced fluid increases the fluid’s viscosity. The increased shear rate increases the viscosity of the fluid thus creating more friction.
This allows the fluid to transmit torque. Note that typical diff gear oil is not applicable here so a special
silicone based oil is permanently sealed into the factory LSD unit while normal diff gear oil still lubricates the ring and pinion gears.
However the MX-5 Miata VLSD typically doesn't get hot enough during everyday driving to work effectively.
 | A viscous LSD was only available for the 1.6 engine equipped cars with the 6" diffs |
Differential Centres - Torsen
The 1.8 differentials came from the Mazda factory with the optional and more desirable
TORque SENsing LSD centre or Torsen for short.
The
Torsen Type I was on offer in the earlier NA 1.8’s and the
Torsen Type II was made available from around 1995 through to the end of the NB’s life.
It is commonly believed that the Type I is more conducive to locking under power, while the Type II is weighted toward locking on deceleration. The type II is generally considered to be stronger.
The Type I Torsen is the traditional worm gear unit with a torque bias of about 2.5. The Type II unit has a different design with three sets of drive gears that are mounted with their axes parallel to the ring gear axis.
The Type II is
simpler and less expensive than the Type I to manufacture.
Take note that the differential in the turbocharged Mazdaspeed Miata (delivered in the US) and the turbocharged SE MX-5 (in Australia) received a different Torsen centre - these cars were also delivered with larger diameter axles (see also - Honda S2000 below).
 | The axle hole of a Torsen Type I diff has a hole all the way through. The Type II is similar but with a small hole right in the center. |
Differential Centres - Clutch Pack
Aftermarket manufactures like
OS Giken, Kaaz and Cusco offer Clutch Pack LSD’s to suit the Mazda differential.
While the Torsen LSD's are capable and cost effective offerings, the clutch pack differential centres are certainly become more useful when you are starting to look at
higher power levels over about 200rwhp.
Clutch packs wear with usage. An additive is required in the differential oil to allow the clutch pack to function correctly.
These differentials will also tend toward inducing understeer in a car with the application of power.
Advanced drivers only!
 | A clutch pack diff centre is a great choice for track and drift cars and/or those with high power levels. |
Differential Centres - TOCHIGI FUJI SUPER LSD
The
TOCHIGI FUJI SUPER LSD came from the Mazda Factory fitted to some later 2003+ naturally aspirated NB's. (It is believed that the 2003+ turbocharged Mazdaspeed Miata delivered in the US and the turbocharged SE MX-5 in Australia continued to receive a Torsen centre - these cars were also delivered with larger axles.)
While it used the same housing as the normal 7" diff found in the other 1.8 engined vehicles, the
differential unit itself is different.
The TFS diff is a form of
clutch LSD but is generally considered to be only a small upgrade over the factory offered Torsen diffs.
The TFS uses cone clutches made of hardened metal which can transmit higher torque levels for a given diameter than traditional flat plate clutches.
 | There were a few early cases of the TFS differentials shedding clutch plates and subsequently requiring replacement. |
Extra Information - RX-7 Differential Swaps
A Clutch Type LSD was fitted in the 1986 to 1991 naturally aspirated RX-7 which will fit directly into the 1.8 differential of the MX-5 Miata - these are considered to be a good value upgrade for those who want more bite at the track.(84-85 models also fit, bit are not the right part as they are for a solid axle and as such do not have provision for the driveshaft circlips)
The 1986 to 1991 naturally aspirated RX-7's use an aluminium housing that is directly swappable with the MX-5 Miata provided the large 'donut' differential bushings of the MX-5 Miata are used.
There were also some naturally aspirated RX-7's from around 1989-1991 that were fitted with a Viscous LSD and while they will fit the 1.8 MX-5 Miata diff, these units aren't worth the trouble.
The turbocharged RX-7 models of the late 80's and early 90's all used differentials that may be somewhat similar but in some way or another require considerable fabrication to fit into a MX-5 Miata. This may include custom driveshafts or half shafts, or PPF mounts
Extra Information - Honda S2000 Differential Swaps
Honda used the same 7" rear for their S2000 as the one that was fitted to the 1.8 Mazda MX-5 Miata. While the rear housing is different and the axles are larger, the ring and pinion gears are the same and can be directly swapped.
The exception being the turbocharged Mazdaspeed Miata (delivered in the US) and the turbocharged SE MX-5 (in Australia) which received the same diameter axles and differential centre.
Note that the Honda R-type Torsen also has a clutch disk which is used to pre-load the worm gear. With some clever engineering one could adapt the larger S2000 halfshafts and stub shafts to mate to the MX-5 Miata hubs for a stronger rear end.
 | The ever popular Honda S2000 also runs the same 7" differential from the 1.8 MX-5 Miata. |
Extra Information - Speed Sender
If you’re considering changing the final drive ratio of your differential, it will effect your speedometer. The speedo sender located in the gearbox can be changed to compensate for the change in gearing to ensure your speedometer maintains the correct reading.
The NA's run a mechanical speedo with a cable drive from the gearbox sender to the dash cluster. These can become noisy or fluctuate when old and may require lubrication or replacement.
The NB cars came fitted with electronic senders are a variable-reluctance sensor. The VSS signal goes directly to the dash cluster which then modifies the 'dirty' VSS signal and outputs a square wave that the ECU, Cruise control module, etc can read.
 | Changing your speedometer sensor is a simple job and will ensure you maintain the correct reading when changing your final drive ratio. |
Extra Information - Part Numbers
| Part | Part Number |
|---|
| Diff Axel Seal |
MA02-27-238A |
| Pinion Seal |
MA02-27-165A |
| Inner Pinion Bearing |
M025-27-210 |
| Outer Pinion Bearing |
0755-27-210 |
| Axel Side Bearing |
0221-27-350 |
 | An exploded view of all the components of the MX-5 Miata differential. |
Extra Information - External Links
