New bulletproof transfer case option for Mitsubishi Evo

The OEM gears in the Evo transfer cases are fine for stock applications, but are prone to pitting, galling and shearing in high torque applications and particularly in sustained motorsport use. This shows up as the characteristic “death whine”.

IMG_8559Finally, we have a real solution to this problem.

Together with Brena Corse, we can now offer transfer case crown wheel and pinion options that are of unbelievable quality and durability. These are made in Italy on the best machines possible, by a maker who has supplied to Group A factory rally teams, and OEM supplier to Ferrari and Bugatti.


Due to the setup procedures required for the unique Brena gear profile, we are unable to offer the transfer case crown wheel and pinion sets as a stand alone item for sale. They must be installed by us at Neat Gearboxes (Adelaide, South Australia) to ensure correct fitment – you can contact us here.

What you get:

  • transfer case stripped and inspected
  • chemical clean components
  • bead blast housings
  • new Brena Corse crown wheel and pinion (choices below)
  • new pinion bearings
  • new pinion lock nut
  • new carrier bearings
  • new seals and O rings
  • Dimple magnetic drain plug
  • ACD clutches inspected and pistons pressure tested
  • assembled to custom specifications to ensure reliable running in extreme applications
  • 700ml NEO RHD 75w90 gear oil (recommended fill for F1, extreme motorsport use)

Suitable for:

Evo 4-6; Evo 7-9; and Evo X

Price (in Australian dollars, includes GST – international customers will save 10%):

ISF option $3,590

Isotropic Super-Finishing (ISF) improves surface finish and reduces oil temperatures. An excellent option for a tough street car, or sprint/time-attack where the runs are not especially long (where oil temperatures are not likely to spike). 800Nm capacity.

Carbon Lafer option $3,990

Carbon Lafer leaves a diamond-like carbon deposit on the surface of the gears, leading to incredibly durable gears even in low oil situations and in extreme temperature situations. Cutting edge technology. Recommended for sustained circuit and rally competition use, or where temperatures are very high. 800Nm capacity.

Drag race option $4,090

The drag race spec gears are made of a special steel used extensively in F1. The key advantage is that the teeth will not break with loads up to, and beyond 1000Nm.

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Finally a real solution for the S2000 diff in Australia

These diffs fail for a couple of reasons:

  • small pinion gear
  • cast iron bearing caps snap under heavy torque loads
  • pinion crush tube collapses, leading to no bearing preload
  • driver abuse


We address the issue of the small pinion gear by strengthening it with shot peening and ISF/REM treatment (Complete rebuild only).

The CT Engineering billet bearing caps stop bearing cap flex and misalignment, and prevent the cast caps from braking.

The solid collar replacement by J’s Racing prevents pinion bearing failure (Complete rebuild only).

Nothing can prevent driver abuse except the driver. While these diffs will be extremely reliable, they will still break if you clutch dump at high RPM with sticky tyres and/or a turbo. Just like any other diff on the planet.


Rebuild Options we offer:

Basic: $1,750


Includes all of the following:

basic rebuild kit (genuine Honda):

  • pinion bearings
  • crush tube
  • pinion seal
  • axle seals
  • pinion nut
  • pinion shim

CT Engineering billet caps (custom machined to housing)

Shot peen original cast iron bearing caps

ARP fasteners

Chemical clean components

Thermal dispersant coating on housing to help the diff shed heat

Meticulous assembly in dedicated clean room

  • set backlash
  • set mesh pattern
  • set bearing preloads
  • all fasteners to factory torque values

Complete: $2,500

This is as close to bulletproof as an S2000 diff will get.


Includes all of the following:

complete rebuild kit (genuine Honda/J’s Racing):

  • pinion bearings
  • carrier bearings
  • J’s Racing solid pinion collar
  • pinion seal
  • axle seals
  • pinion nut
  • pinion shim
  • crownwheel bolts
  • Dimple magnetic drain plug

CT Engineering billet caps (custom machined to housing)

Shot peen original cast iron bearing caps

ARP fasteners

Chemical clean components

Hot tank gear set^

Crack test gear set^

Demagnetise gear set^

Shot peen gear set

ISF/REM treat gear set

Thermal dispersant coating on housing to help the diff shed heat

Meticulous assembly in dedicated clean room

  • set backlash
  • set mesh pattern
  • set bearing preloads including J’s collar setup and shimming
  • dial in LSD and crown wheel to reduce any runout
  • all fasteners to factory torque values


Add new gear set:

Can be applied to either the basic or compete packages. 2 Ratios available (more on request):

4.77:1 $550

4.44:1 $880

These are “genuine” gears, made by Mazda – the same supplier as Spoon and J’s Racing.

We can build your diff with your choice of LSD from reputable companies such as Kaaz and Spoon, too, if you want a more aggressive clutch type engagement.

If your housing or bearing caps are already cracked or broken this will cover the outright cost of a new housing.

You still need to send your diff, even if it’s cracked, so we can use the other components such as the front flange, side screws, rear cover, LSD centre etc. in your rebuild.

The price of the rebuild does not include replacement gears: if you supply a good set of gears we will use those. If yours are broken you need to either purchase a new set, or we may have second hand sets in stock which you can purchase.

^We only prepare used gears in this fashion – it is not required for new gear sets.

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Nissan Silvia S15 6-Speed gearbox “Circlip Mod”

We’ve been working with a few customers over the past few months to come up with a solution to prevent major gearbox failure in the S15 6-speed gearboxes.

Essentially the issue is the same every time: more-than-stock torque loads put excessive lateral force into the 4th gear “circlip” (actually a pair of spacer C clips retained by an outer snap ring) which causes it to chip the retention groove. This leaves 4th gear to freely float across the countershaft and inevitably come out of alignment with it’s drive gear and causes major failure.


Even mildly modified vehicles are susceptible to the problem. In reality it is a design problem rather than a metallurgical one.

We’ve come up with a modification to ensure a stronger countershaft, and is an essential modification whenever one of these gearboxes is pulled apart.

Firstly a brand new genuine Nissan countershaft is machined to make the retaining groove deeper. As can be seen in the photos, the groove goes to the depth of the root of the teeth that it is cut through, and no deeper, to ensure that maximum shaft strength is maintained.



The new shaft is then shot peened to ensure that any stress risers from the grinding process are eliminated and to put a compressive stress layer throughout the shaft to prevent crack formation from occurring.


A new set of C clips is custom machined to match the new groove (lower set), giving about double the thrust surface of the original thrust shims.



You can use this with the original retaining snap ring, and everything is “factory fit”. This system is far superior to welding the shaft and takes into account relieving stress in the countershaft after machining.

This mod is developed and sold exclusively by Neat Gearboxes for $849 including a new shaft, shipped to your door anywhere in Australia. Alternatively we can modify your existing shaft as long as it is undamaged. The price for this is $495 including crack testing and chemical hot tank cleaning. Other associated parts are available, such as rebuild kits, 4th gear replacement and so on – please contact us for any further info or if you’d like to place your order:

We of course offer this mod in the context of a full rebuild, too.

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S2000 diffs: Why they break, and how to stop it from happening (again) – Part 2

We received a customer’s broken S2000 diff last week.

This is the worst one we’d seen so far; clean snapped the centre section of the bearing cap on the crown wheel side off. The usual chewed pinion was the result.

By our reasoning here at Neat Gearboxes, this is the sequence of events that causes this failure:

  1. Hard acceleration is applied by the driver
  2. Heavy load is applied to the crown wheel and pinion (CWP) as the Torsen limited slip differential (LSD) does its job and sends torque to both axles with sticky tyres on the ends.
  3. As load increases, the hypoid gears (CWP) force each other in opposite directions (pinion perpendicular from crown wheel)
  4. This increased side thrust forces the crown wheel and its carrier hard up against the side thrust adjuster screw closest to the crown wheel (see picture)

    the side adjuster screw was forced into the side of the aluminium rear housing

    the side adjuster screw was forced into the side of the aluminium rear housing

  5. The bearing cap is forced outwards and the carrier bearing comes out of alignment
  6. The high grade 12.9 bolts stay put and the cast iron caps eventually give way (see pic)

    the cap closest to the crown wheel snapped clean in two places

    the cap closest to the crown wheel snapped clean in two places

  7. The crown wheel eats the pinion (see pic)

    The result: a destroyed final drive gear set.

    The result: a destroyed final drive gear set.

It seems that locating dowels on the bearing caps won’t be enough to stop this from happening as the load seems to be between the bolts. We have attempted to machine dowels into the housing but alignment is an issue when trying to centralise over a threaded hole, so we’ve had to have a rethink.

We found this interesting: the little bolt that holds the tag that stops the side adjuster screw from undoing itself was completely sheared off and the side adjuster screw was a full turn out (see pics).

The bolt that holds the tag that prevents the side adjustment screw was sheared off

The bolt that holds the tag that prevents the side adjustment screw was sheared off

The side adjustment screw had unwound itself a full turn

The side adjustment screw had unwound itself a full turn

We have had a rethink and are presently making a prototype “assembly” that prevents the bearing caps from flexing apart – can;t give too much away, but stay tuned, more to come.

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Subaru BRZ / Toyota 86 Final Drive Swaps: 4.556:1 and 3.73:1

We’re proud to offer one of the first comprehensive final drive (diff) ratio swap packages for the BRZ/86. We reckon this is one of the best and most noticeable modifications you can do.

We presently offer two ratios: 4.56:1 or 3.73:1

The 4.56:1 Final drive ratio swap is the best option for those who wish to keep their modifications naturally aspirated. This gearing represents a net 11% increase of torque to the wheels over the (Australian) standard 4.1:1 ratio, regardless of other engine modifications, across the entire RPM range. No other modification comes close to the return you get for this kind of money.

The 3.73:1 ratio is for forced induction applications. Lengthening the final drive ratio makes use of the added torque spread that your supercharger or turbo brings, and matches the characteristics of a force induced engine to your BRZ or 86. We strongly recommend opting for the “complete Neat” package to take advantage of our unique strengthening processes which will ensure reliable running with forced induction applications.

Essentially we offer two options.

Standard Rebuild

The “Standard” kit is anything but basic; it is an exacting factory-spec swap. We rebuild your diff to exact factory tolerances – no shortcuts. We check and adjust mesh pattern and assemble in our dedicated clean room just like all of our gearboxes and diffs. Here’s what’s included:

(All parts genuine Toyota/Subaru):

  • Brand new crown wheel and pinion in a ratio of your choice (4.56:1 or 3.73:1)
  • Front and rear pinion bearings
  • Crush tube
  • Pinion nut
  • Pinion shim
  • Crown wheel fasteners and lock tabs
  • Chemical clean components
  • Set pinion depth and mesh pattern
  • Reassemble to factory specs

Price: $1,499 (3.73:1) / $1,749 (4.56:1)

Complete Neat

The “Complete Neat” package is a bundle of all of our tricks and improvement processes in one complete package. Our unique processes yield stronger and more reliable drivetrain components. All processes are completed in-house so we control the quality. Here’s what we include:

  • Everything in the “Standard” kit, plus:
  • Side carrier bearings and seals
  • 2 x Dimple magnetic plugs (1 x fill and 1 x drain) to keep your oil free of contaminants
  • Custom solid pinion spacer machined to suit each unique housing. This eliminates the factory crush tube which can distort under extreme loads causing catastrophic diff failure.
  • Shot peen gear set using SAE-J2441 guidelines – 30% increase in fatigue resistance
  • Isotropic Super-Finish (REM/ISF) gear set – 5 degrees Celcius temperature reduction, friction reduction and further improved fatigue resistance.
  • Bead blast housing
  • Baked Thermal dispersant coating on cast iron housing to further assist temperature control

Price: $2,349 (3.73:1) / $2,599 (4.56:1)

Check out to find out more about our unique set of services. Interstate and overseas shipping can be arranged at very competitive rates. Prices include 10% GST – international customers are exempt from this charge.

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Honda S2000 gears

These Honda S2000 gears have been shot peened and Isotropic Super Finished in-house at Neat Gearboxes. This leaves the gears around 30% stronger, with the smoothest possible surface finish available. This lowers friction, reduces operating temperatures of diffs and gearboxes, and leads to more power on the ground. Not bad for $349 shipped anywhere in Australia, including chemical hot tank cleaning and crack testing under UV light as well.
Check out for more info on our peen and polish packages.

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S2000 diffs: Why they break, and how to stop it from happening (again)

These last few weeks we’ve been working on finding ways to improve the S2000 diff. I’ve always loved these cars, even though they are convertible and I’ve never been a huge rag top fan. But there’s something about a 9,000 RPM redline that appeals, and combined with what I think is a fantastic looking, light, rear-wheel drive platform, it’s a car that I wouldn’t mind owning.

A customer recently approached me saying that he was having trouble holding his diff together on his track-driven S2000. I did a little searching around and found similar murmurings on online forums around the world. The pinion gear is usually the thing that breaks first, which can cause pretty serious collateral damage, often leaving owners with repair bills in the thousands. People often make the assumption that the gears are weak, but after a fair bit of investigation, I think that is misinformed – although there’s always room for improvement, particularly through Isotropic Super-finishing (ISF), a service that Neat Gearboxes are proud to offer.

Presently there’s only a few (fairly unattractive) options for S2K owners in Australia and the rest of the world who want to put more power or traction through their diff:

  1. Swap the Honda diff out for known strong options such as a Nissan 300zx or Ford 9” rear end. The mounting issues and cost is heavy, and so is the extra weight. It’s also not Honda, which irks purist owners, understandably. It is a flagship vehicle, after all.
  2. Send a core to the States for the Comptech bearing cap upgrade, or have one sent here for the cost of the work plus a core charge. Freight/customs is a headache on a used item. Those boys clearly do top work, and only a few of their diffs have failed in high power applications. But to be frank, looking at their design, we here at Neat Gearboxes started to wonder what, exactly, a bearing saddle does (more on this below).
  3. See the diff failing every now and then as cost of ownership. Just put a wrecker one in whenever things go bad. Not only is this expensive, it’s also potentially very disruptive. You may miss out on a track day race, or your daily drive could be off the road for a considerable amount of time while you change the diff over.

We decided to do some investigations ourselves, to see where things go wrong. After examining the case, we see a glaring weakness in the S2K diff: The bearing cap fastener bores measure just over 10.5mm, while the fastener shank measures just under 10mm. This leads to the cap being able to laterally “walk” over 0.6mm – see the picture.


What this means is that the bearing cap depends wholly on the under-head tension of the bolts to “stay put”. Heat, which causes material expansion, and the lateral forces from a helical gear set driving themselves apart, both make this a tough ask for those two M10 bolts that have to stop the diff centre from exiting the rear of the vehicle. As soon as the caps come out of alignment, so does the carrier bearing. Once that happens, the gears are out of alignment, and, BOOM! It doesn’t matter how strong your gears are – if they come away from each other enough, they’ll eat each other in a hurry, and the smaller guy (the pinion) always loses.

Taking an example from engines, the main bearing caps for the crankshaft are not only held down by bolts or studs, but located by dowels so that the bearing caps can’t go walking. So, we’ve decided to come up with a way to accurately and cost effectively introduce bearing cap dowels and stop those pesky bearing caps from walking away.

Stay posted, more to come.

And remember, to get you up and running we have repair kits and final drives in stock. Bearing kits start from AU$249, and the 4.77 gear set is just AU$429.

See for details.

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Shot Peening Gears

A little clip explaining the benefit of shot peening gears, whether for motorcycles, tow cars, 4WDs, track cars or just your street ride.

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Amazing new build video from Red Bull Racing F1 team

Very cool new video put out by Red Bull Racing.

Amazing stuff, and a rare look inside a gearbox at 2:10 onwards, so super exciting for us.

The greenish glow on the gears is actually where the engineers are checking for cracks with a UV light, called magnetic particle inspection. We use the same method  here at Neat Gearboxes -check out more info at

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We’re excited to be launching our website soon. Here’s a first glance at our logo and some of the things we can do.

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