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Helical Cut Synchro Gear Kit 5MT

PPG's synchro gear kits have proven themselves to be the optimum solution for strengthening Subaru's weak 5-speed transmission when streetability is a primary requirement. Superior quality, design, and manufacturing ensure that PPG's gearsets outperform the competition. Available in separate 1st/2nd and 3rd/4th kits in order to allow freedom to mix and match with OEM or other PPG gear tooth/engagement options. Suggested for applications up to 450whp.

Usually ships in 1 to 2 weeks.

Manufacturer: PPG

Applications:

  • Subaru 5-Speed Manual Transmission (AWD) MY1999-2014

Are these gears are a direct fit in my Subaru 5-speed? The answer depends on the model and year. These gears are designed around the early (1999-2002) WRX transmission so when fitting to other models may require backdating some parts. Additionally, the gear width of 1st,2nd, and 3rd is narrower than the later gears. If changing only 1st and 2nd gears on MY2003+ either MY2002 WRX 3rd and 4th gears must be used or some custom work is necessary for correct fitment. We suggest only experienced PPG installers attempt this work. Please contact us for additional information.

How does a synchronizer function? A synchronizer gear set uses a baulk ring (also known as a blocking ring) to prevent the selection of the gear until a friction surface on the baulk ring has synchronized the speed of the gear to the speed of the output shaft. The synchronizer's operation relies primarily on the viscous drag of the fluid but as the fluid between the baulk ring and the mating surface on the gear is squeezed out friction between the baulk ring and the cone becomes the only synchronizing mechanism. An attempt to shift too quickly or with too great of a speed differential (mis-shift) will cause wear and damage to the baulk ring and potentially the selector engagement teeth making subsequent shifting into that gear more difficult. A synchronizer is very sensitive to the viscosity and the friction characteristics of the fluid and the selection of the wrong fluid can cause shifting issues.

How does a dog type gearbox function? A dogbox has no synchronizing function. A set of dogs (basically raised metal blocks machined on the face of the gear) engage instantaneously with a set of matching cutouts in the selector sleeve. The cutouts on the sleeve are much wider than the dogs so the dogs will drop in to the cutouts easily. A slight back cut on the dog and sleeve prevents the dogs from disengaging when under load. The speed of the shift is limited only by how quickly the driver can move the shifter and in some cases the shift can be made without disengaging the clutch. Shifting must be quick and deliberate or the dogs will clash which damages their corners. With enough damage the dogs will not stay engaged under load and will need to be replaced or re-cut. The life expectancy of the dogs is entirely dependent on how well it is shifted. However, a dogbox is preferred for competition use because it allows faster shifts and can allow shifts to occur even under the most adverse conditions that would destroy a synchronizer.

What is a sequential gearbox? A sequential gearbox is a dogbox with a special shifter mechanism. The shifter moves only forward and backward (it is not an "H" pattern with separate gates like a traditional gearbox). The gear selection must be done in sequence (hence "sequential"). Pulling backward on the shifter will shift up while pushing forward will shift down. To put the transmission in nuetral shift down to 1st and then down again. Reverse is selected from nuetral after releasing a lockout lever. The advantage of a sequential gearbox is to provide the quickest and most mistake-free shifting. It is impossible to accidentally downshift into an incorrect gear and drastically overrev the engine.

What is the difference between a straight cut and helical cut gear? This is a representation of the tooth profile. A straight cut gear is machined perpendicular to the faces of the gear...or basically straight across. A helical gear is machined along a helix and will have some angle and curvature to the tooth. Straight cut gear teeth engage one at a time all at once. When each tooth engages, due to the backlash in the gears, a clicking noise is generated and as this happens one after another repeatedly at high speeds the result is the characteristic gear whine noise. Helically cut gears engage gradually with some sliding motion.

What are the advantages and disadvantages to the different tooth profiles? A straight cut gear is typically used for a racing application because when load is applied to the gear teeth there is no, or very little, axial thrust component to the resulting forces generated. A straight cut gear is therefore more efficient as the power wasted in the bearings is reduced. Additionally, a straight cut tooth profile is more forgiving to shaft deflections that allow the gear teeth to separate from each other under load or heavy shock. A helical gear is quiet with little or no whine (depending on the helix angle as well as the accuracy of the tooth profile). This makes it more preferrable for a road car. Additionally, a helical gear will typically have a greater load capacity (assuming identical gear tooth pitch and other dimensions) although as mentioned will have much less tolerance to gear mesh issues due to gear tooth separation conditions.

What is a close ratio gear set? Close ratio means the ratio difference between adjacent gears is smaller so the rpm change with each shift is reduced. This allows the engine to operate within a narrower rpm range which may be beneficial for acceleration particularly if the engine has a "peaky" power curve. In general a close ratio set will be more fun to drive on tight twisty roads. However, the taller 1st gear demands that the clutch be slipped a little more in order to get the car moving and the shorter 5th gear will raise the highway rpms and potentially reduce the fuel economy.

How strong are the PPG gears? Compared to OEM and some lesser quality aftermarket gears PPG uses a special tooth profile, larger tooth dimensions, higher quality materials, and more tightly controlled heat treatment and stress relieving processes. Helical gear profiles use a shallow helix angle to reduce axial loads and improve the operating reliability at larger shaft deflections. Overall they are some of the strongest gear set options available. However, no gear set is indestructible. One of the main limitations of the Subaru 5-speed transmission is the lack of rigidity in the shaft support bearings. As a result, with proper preparation a Subaru 6-speed can be made stronger than a 5-speed.

Is it possible to buy individual replacement parts if necessary? Yes, please contact us to obtain pricing.