Since the late 80’s, the G25/G5M transmission has been fitted to a number of vehicles including the 323/Familia, 626/MX6 and others. The G25/G5M series are a 5MT with variants including a number of gear ratio selections and varying final drive ratios. Throughout the model’s lifespan, single cone synchronizers were used early on with the gradual fitment of double cone synchronizers fitted to the later vehicles. This is the transmission of choice when the BPT engines or turbochargers are fitted to the BP engines in the Mazda 323/Familia/Protege or Ford Escort/Laser vehicles.
Although much stronger than the smaller F-Series transmissions, the G-Series torque capacity is still not sufficient to handle the extra load and shock provided by the fitment of more powerful engines and aggressive clutches with the most common failures being 3rd/4th gears, transmission case and broken differentials. The most notable weaknesses in the G-Series transmisssions is the general strength of the 2nd~3rd gear, differential planetary gears and pin. With more powerful vehicles, the case structure becomes a problem with the thrust load provided by the helical gears sometimes causing case failure including cracks in the housing and sometimes destructive failure of both housing and gearset.
For powerful street driven vehicle, we have the 1st~4th synchromesh engagement straight cut gearset available as a normally stocked item. Features and options include a number of ratios and options such as double synchronizer, needle roller bearings and shift stops on most gears to prevent overselecting for the inclusion of the very latest transmission technology and innovations in your upgrade.
– Tooth profiles that reduce noise, wear and load forces on the standard OEM transmission housing
– Multiple piece input shaft for flexible ratio choice and changes
– Shift retaining rings incorporated into design to eliminate over selection and synchronizer baulking
– Optional needle roller bearings with matching gears for minimal friction, noise and maximum load capacity and reliability
– Optional double synchro gears which enable the use of the latest dual cone baulk rings for the smoothest and quickest shifting
– Retension of OEM 5th gear assembly provides OEM NVH levels during cruise and freeway driving
– Straight cut gears for maximum power transmission and minimal thrust loads exerted on the OEM transmission case
– 3rd and 4th gear sets available individually as completely separate upgrades if desired ($940 AUD (ex GST) per speed)
– Billet crown wheel and pinion shaft $1,840 AUD, $1,480 When purchased with a Full Gear Set
– Billet reinforcement cups Optional – $650 AUD
– No extra cost custom ratios
– 1st: 2.55, 2.80, 3.11
– 2nd: 1.57, 1.83, 1.85, 1.90, 2.0
– 3rd: 1.24, 1.31, 1.60
– 4th: 0.90, 0.96, 1.29
– 5th: 0.78, 0.95, 1.05, 1.16 Optional custom ratios available
– Final Drive: Optional 3.93, 4.00, 4.08, 4.13, 4.43
– All Mazda vehicles that use the G25M and G25MR transmissions including Protege, 323, Mazda 3, MX-3, 626, Mazda 6, MX-6 and others
– Factory Service Data Specifications, especially preload specifications, must be used when installing gearsets
– OEM hubs may need clearancing with suitable machine tools in order to retrofit double cone synchroniser assemblies
– Genuine Mazda 2nd, 3rd and 4th gear dual cone synchronizer baulk ring assembly (GC01-17-26ZB)
– When fitting needle roller gears to the OEM input and pinion shaft, journals must be ground to the following specifications.
1st gear pinion shaft – 37mm
2nd gear pinion shaft – 33mm (Shoulder adjacent to journal must be kept to retain the factory circlip/retainer)
3rd gear input shaft – 33mm
4th gear input shaft – 30mm
(Any helical oil grooves remaining may be left if still visible after grinding)