MRT Unbreakable Gear Sets

Parts background
MRT Performance has been working on the dog gear change set for some time now and completed final testing in their Impreza STi in October 2000. We can also offer upgraded synchromesh kits in several ratios as well as individual components to replace damaged parts that will fit with standard factory components (OEM)

For drag racing, road or track use, we have several gear sets to choose from, whilst the rally ratios are fun for a while, the rally gear set requires an extra gear change on the 1/4 mile and generally drag and highly modified track cars have more power than rally cars (the restrictor is a huge loss!) so the taller geared sets are better. For group A rally cars or open class rally cars (EG Australian PRC) we recommend 4.1 differentials and the related gear set.

Description
The gear set we offer is the gear set we use in our rally car, it uses straight cut (spur) gears, this can be noisy on trailing or loaded throttle, however it can be tolerated in a road car.
A spur gear has no end thrust ( like a OEM helical gear that "generates" end thrust), has a wide contact patch, is stronger and has less power loss. The spur gear design we use is the latest in tooth technology and is superior to all other brands.

If noise is a major concern we would suggest a synchro gear set with heavy duty gears or a Synchro gear set that has a spur gear on first and or second gear, (please contact us for a list of parts that suits this). Note, its not the dog drive that makes the major noise, its the spur gear design. Helical gears are quieter, but they generate end thrust that increases bearing load and can bend the Subaru gearbox steel main thrust plate (near the transfer case) in extreme circumstances. The gear set comes complete ready to fit, sometimes gear casings may need some small machining to provide clearance however, no heavy or accurate machining is required (like other brands) Gearbox casings vary slightly depending on factory tolerances.

The gears are slide on, onto the output driven shaft, meaning they are not press fit (like OEM and other brands), simply undo the shaft nut and they will slide off! All driven (1st to 5th) gears have caged needle roller bearings to reduce power loss and ensure accurate meshing of counter gear, and are cut to the latest F1 tooth profile. Swapping of gear ratios is simple and requires no special tools nor does the gearbox need to be reset for backlash. The dog rings are available (like all parts), separately. An optional HD shift fork kit will be available shortly. However the gear set works with std Impreza GT or WRX shift forks, (for STi applications, MRT can supply new OEM shift forks).

Will it fit and work in my gearbox housing?
The gear set will fit either Impreza WRX, GT, STi 22b or USA spec RS (non turbo 2.5 litre), and some other similar gearbox's as well as Liberty / Legacy (turbo and non turbo) gearbox's, in some cases small changes may be needed to the bearings or shift forks.

We have not confirmed if the gear set will fit into the dual range gearbox as yet. The gear set will fit all the current turbo gearbox's including the new stronger casing that came out in 1999 with revised rear transfer case, as yet we have not developed one to suit the September 2000 onwards 6 speed gear box.

It will work with either Viscous or Electronic centre LSD's, and it will work with either standard open or mechanical front differentials. (the front differential pinion shaft is not part of the kit, and it (the pinion) matches our gear set.

Is size important?
The gears are slightly larger than OE, however we have not gone for a wider gear as a "marketing exercise", the gears in this set are actually larger than a F1 gear , so we know they will be strong enough. However if in the case of highly stressed applications, we have the future option to make the gears up to %30 wider (than now) and still maintain the same reverse gear width. Special orders may be made if required.

Some other brands supply much wider gears to make you think they are better, however the downside of this is that the reverse gear is less than HALF as wide as the OE part. If you use this, be very careful in reverse gear!! For rally use, chances are you will certainly break reverse gear.

Comparisons to other brands
The MRT Gear set maintains original size reverse gear, some brands may strip reverse gear in competition if the car goes off the road as they use a gear that is less than half as wide as std.
This is due to to the the fact they have such wide (unnecessary) main gears. The MRT set has slide on gears, some brands still use press fit gears.

Some brands still use a one piece input shaft. (this is known to be a weakness in some applications) MRT uses a two part shaft. Some brands have poor gear selection and can jamb in gear or select two gears at once, in many rallies and road testing the get set we offer has never jammed in gear. Many other brands have little or no warranty or no warranty for motorsport use. MRT offer a full 2 year warranty on gear breakage even in drag and motorsport use! Some gear sets simply can not be used in FIA homologated events our gear set meets the 2001 regulations. Some other brands need massive gear casing machining, with specialist equipment to allow the gear set to be fitted. The MRT gear set needs no case machining (although some casings do vary and require slight clearance mods).

Ratios
The gear sets are available in common Group N homologation sets to suit either 4.1 or 4.4 ratio front differentials. MRT indicates these kits meet FIA Group N rules for 2001, however as in normal motorsport use, its in your interests to ensure you understand the rules and check details to meet local requirements.

Separate ratio sets are available for road / drag / race car applications where the short ratios as in Group N are not suitable, these gear sets are similar to the latest ver 5/6 Sti road set, however a little shorter. The final drive ratios are similar and also available for cars with front 4.1, 3.9 or 4.4 differentials

Gear Ratio Data Sheet - PDF

Download the PDF file, then click on the pic -->
for a full size graph.

Ratio sets now available
Note, 4.4 is the common differential ratio for STi and the newer model high performance Subaru's after 1998. If your car has the large rear (R180 type) differential and two spot (rear) fixed type callipers then you probably have the 4.4 front (and rear) differential. If you have a GT or WRX or early STi then you probably have 3.9 or 4.1 front differentials. If you have a early RS Legacy or Liberty turbo then your car will (probably) have a 3.9 front, 3.5 rear (transfer case ratios vary). NOTE: Rear diff ratios also vary compared to the front.

Ratio sets
For specific ratio sets, please contact MRT direct, for rally use we carry FIA homologated ratios, whilst for street, drag and track use we have specific designs that we don't publish here. e-mail us direct Info@MRTrally.com.au

Availability
MRT carry some gear sets in stock but due to demand whole gear sets may take up to 6 weeks to ship to you, please refer to us to allow us to meet your deadlines. In certain circumstances we can assist in urgent situations.

Assembly
MRT Performance offers their extensive experience for preparation of your Subaru Gearbox. We can either repair, rebuilt or update your gearbox with any of above options.
We also carry many near new and second hand road and close ratio gearbox's in stock.

Options
Our factory carries blank gears in stock and can machine special ratios on demand.
An optional progressive locking front differential is available, or we can offer either STi, Kaaz, Cusco or other Mechanical plated front centre and rear differentials. We also carry several Viscous centre differential options in stock (as well as other brands) and also offer free testing of centre Viscous differentials should you need it. Contact us for advice.

Separately we also offer gear assembly gasket kits as well as assembly sealant should you require it. MRT also offer heavy duty clutches, Billet steel flywheels and STi heavy duty gearbox / engine mounts to save you fitting time and labour during your gearbox upgrade.

MRT Unbreakable Gear Sets - 2