Transmission FAQ

The primary purpose of an upgraded gearset or transmission is to provide increased strength over the OEM unit or to utilize different gear ratios better suited to the particular racing style of the end user.

What is some good background transmission information?’s transmission walkthrough’s clutch walkthrough’s gear walkthrough
Gear lingo’s gear ratio walkthrough’s differential walkthrough
Subaru specific differential information
AWD information
Subaru’s AWD walkthrough
Subaru’s AWD walkthrough

What type of gears are available? There are two types of gears commonly used in transmissions based on their teeth engagement pattern.

Helical Gears: Helical gears are used in standard factory transmissions. The teeth on Helical Gears lie along a helix, the angle of the helix being the angle between the helix and the pitch cylinder element parallel with the gear shaft. Helical gears can connect either parallel or nonparallel non intersecting shafts.

Helical Gear example:

Spur gears (also known as straight cut gears): Spur gears have straight teeth and are used to contact parallel shafts.

Spur Gear example:

What are the differences between gear types? Primarily noise. Spur gears have a high pitched whining noise associated with them similar to the noise reverse gear generates. Helical gears are generally as quiet as the OEM gears. With both gear types though, the tone and volume of any additional noise can vary between manufacturers.

Which gear type is stronger?
This is one question without a clear answer. The theory behind helical gears being stronger is because the contact between mating teeth increases more gradually and more teeth are in contact at a given time compared to a spur gear. So, looking at this further, helical cut gears would be stronger than straight cut gears of the same width as more than just one tooth will be transferring the torque. Helical gears have one disadvantage when compared to spur gears. When they are loaded a side thrust is created that must be absorbed in the bearings. There is also a strong case represented by spur gears as they generally have fewer, but larger and theoretically stronger teeth. It is probably best to choose the best gear type based on manufacturer ratings or noise preferences rather than gear type.

What does a Subaru transmission look like inside?

1. Mainshaft
2. Mainshaft support bearing
3. 1st drive gear
4. Reverse drive gear
5. 2nd drive gear
6. 3rd drive gear
7. 3/4 selector hub
8. 4th drive gear
9. Mainshaft thrust bearing
10. Output shaft thrust bearing
11. 4th driven gear
12. Speedo drive
13. 3rd driven gear
14. 2nd driven gear
15. 1/2 selector hub
16. 1st driven gear
17. Pinion shaft support bearing
18. Pinion
19. Ring gear
20. Stub axle
21. Front LSD

Figure notes: 5th gear is not shown in this example. It would be located to the left of items 9 and 10 in similar fashion to the other gears. Though hard to see, items 7 and 15 each contain a shift fork that actually select the gears. Between items 4 and 5 is the reverse idler gear which slides forward during engagement causing item 15 to spin the pinion shaft the opposite of mainshaft rotation. Items 18 and 19 are known overseas as the Crown Wheel and Pinion (CWP). This is noted to avoid any possible confusion if you should happen to hear/see this term at a later date.

What types of engagement are available? This is a common source of confusion when searching for information on transmissions. There are two types of engagement: Synchro and Dog.

Synchro engagement (also known as synchromesh) is what most passenger cars use.

a. Smooth operation on the road
b. No special driving style required

a. Synchros and shifting forks can break when abused and shifted aggressively
b. Slower to shift vs. dog engagement

Dog engagement is what most race prepared vehicles use.

a. Engage at any rpm
b. Allows for wider gear design
c. Will flat shift (Flat shifting is a practice where the clutch or gas do not need to be totally lifted in order to shift. Users will slightly lift one or the other to unload the dogs to allow a very fast shift)

a. Difficult to drive on the road
b. Recommended only for race use
c. Special care required under normal street use

What is a dog box? A dog box is the term for a transmission utilizing a dog engagement. A dog box can have either helical or spur gears or both.

What is a half dog box? A half dog box utilizes a combination of synchro and dog engagement. It depends on the manufacturer and customer preferences. Generally speaking, the first and second gears are dog engagement and the rest of the gears are synchro engagement. A half dog box can have either helical or spur gears or both.

What is synchronizer (synchro) engagement?

Synchros are synchronizers inside the transmission. These are the actual parts that move when you move your gear shift from side to side and back and forth. Their job is to connect the gears of the transmission to the shafts that they ride on and lock them together. This must be done at a gradual rate or the gears will grind. The synchronizer drives a cone shaped metal piece against the gear and starts the gear spinning. It accelerates it to the speed of the output shaft. When the gear reaches the speed of the output shaft, the synchro meshes completely with both of them and directs drive through its splines from the gear to the output shaft or vice versa.

What is dog engagement? Dogs are basically no more than cogs on a slider. The shifter pushes them into a receiver ring which engages the gear it is attached to. There is a separate dog and receiver for each gear in the transmission. On a racing transmission, there is a lot of “slop” (the gaps in the receiver are a lot larger than the teeth on the dog), which makes it easier to move into and out of the gears at higher RPMs without fully engaging the clutch.

Can a dog box be driven on the street? Though generally reserved for race applications, many users drive dog boxes on their daily driven vehicles. To do so, you need to learn proper shifting techniques and rev matching skills to decrease wear on the dog gears. The Shifting FAQ, this article, local personnel, or your transmission professional should be able to provide assistance with proper shifting techniques. This is one decision that should not be made lightly. If there is the slightest doubt in your mind as to your technique or attitude towards a daily driven dog box, you should opt for a synchro engagement transmission. Another thing to keep in mind is that a dog box is definitely not an option for a vehicle that sees occasional use by others such as your spouse, friends, visitors, valet, etc.

Can I get a sequential gearbox? Yes, but start saving your pennies. The Prodrive unit is $75,000, is lease only, and requires rebuilds every 1000 miles. KAPS has a unit for the bargain price of 22,000 Euros. Modena did make a special paddle shift sequential unit, but it is unavailable for purchase. Ikeya makes a sequential conversion kit for ~$1400 that converts the normal H pattern into a sequential pattern. SQS makes a 6MT sequential for ~$2500. MUCH thought should be given to these options though as they are unproven in the United States, probably require pricey professional installation, and they encourages faster shifting which is more damaging to gears due to the increased shock load they introduce.

What is the biggest transmission misconception? That when you shift gears, you are physically engaging the teeth of the transmission. As seen in the picture above, the teeth of your transmission are always engaged, meshed, and moving. When you shift gears, what you are doing for both dog and synchro engagement is engaging the sliding mechanism inside the gears to apply power to the selected gear. When this occurs, a load is generated in that gear and forward motion occurs.

What is the second biggest transmission misconception? Case flex occurs within Subaru transmissions. Here is how the Subaru 5MT transmission case appears removed from the vehicle:

Top view

Side view

The front transmission section houses the gears and is opened by removing the left and right half shells to expose the gears. These shells are bolted to each other as well as held in place by being bolted to the engine block and the rear transmission section which is another solid piece. Looking at the construction, it is impossible for the housing to flex.

Even if flex occurred, the gears sit on top of each other, so if flexing to any degree occurred, the gears would actually come together firmer due to gravity than apart as some contend. The premise of case flex when looked at from a construction aspect is a moot point and aside from the evidence listed here, there are any number of other reasons in the internal construction that any transmission professional can go over in further detail.

Who makes gear sets?
Andrewtech Automotive (PPG custom)
APS (link goes to a retailer as this product is not on the APS website)
Albins Off Road Gears (makers of Possum Bourne gears)
BPM (No longer sells gears)
Chalak gears were named after their designer, Haysam “Sam” Chalak and are now sold under the company he works for, PAR.
Gimmie Gears (Gears have been discontinued until further notice)
Hewland (makers of Prodrive gears)
Holinger Engineering
MRT Performance
Modena Engineering
PAR (Precision Automation Robotics)(makers of TRP gears)
PPG (Pfitzner Performance Gearbox)(makers of TurboXS gears)
Possum Bourne Motorsport
S&J Automotive
STi (link goes to a retailer as STi does not have gears on their website)
TRP (Tony Rigoli Performance)
Zero Sports

What gear ratio choices are available?

3.636 (1st) 2.375 (2nd) 1.761 (3rd) 1.346 (4th) 0.971 (5th) 0.756 (6th) 2004-2006 STi (USDM)
3.636 (1st) 2.235 (2nd) 1.521 (3rd) 1.137 (4th) 0.971 (5th) 0.756 (6th) 2007+ STi (USDM)
3.454 (1st) 1.947 (2nd) 1.366 (3rd) 0.972 (4th) 0.738 (5th) 2001-2007 Stock WRX
3.166 (1st) 1.882 (2nd) 1.296 (3rd) 0.972 (4th) 0.738 (5th) 2008 Stock WRX
3.454 (1st) 2.062 (2nd) 1.448 (3rd) 1.088 (4th) 0.780 (5th) Stock RS
3.166 (1st) 1.882 (2nd) 1.296 (3rd) 0.972 (4th) 0.738 (5th) Stock Legacy GT
3.166 (1st) 1.882 (2nd) 1.296 (3rd) 0.972 (4th) 0.738 (5th) STi (Non-RA) (5 speed)
3.083 (1st) 2.062 (2nd) 1.545 (3rd) 1.151 (4th) 0.825 (5th) STi RA (5 speed)
3.167 (1st) 2.267 (2nd) 1.667 (3rd) 1.250 (4th) 0.964 (5th) Kaaz
3.180 (1st) 1.940 (2nd) 1.350 (3rd) 0.966 (4th) 0.740 (5th) Chalak (now PAR)
3.270 (1st) 2.286 (2nd) 1.667 (3rd) 1.238 (4th) 0.958 (5th) MFactory
3.180 (1st) 1.910 (2nd) 1.350 (3rd) 0.

967 (4th) 0.825 or 0.738 (5th) PAR Street Perf.-Drag
2.916 (1st) 1.910 (2nd) 1.500 (3rd) 1.160 (4th) 0.920 or 0.880 (5th) PAR Rally-Track
3.000 (1st) 2.000 (2nd) 1.480 (3rd) 1.170 (4th) 0.963 (5th) Sport Gimmie Gears
3.450 (1st) 1.940 (2nd) 1.360 (3rd) 0.960 (4th) 0.760 (5th) Street Gimmie Gears
3.000 (1st) 2.000 (2nd) 1.480 (3rd) 1.170 (4th) 0.760 (5th) Sport/Street Gimmie Gears
3.454 (1st) 1.947 (2nd) 1.366 (3rd) 0.963 (4th) 0.738 (5th) APS
2.917 (1st) 2.090 (2nd) 1.556 (3rd) 1.176 (4th) 0.900 (5th) Group N Quaife
2.917 (1st) 2.090 (2nd) 1.556 (3rd) 1.250 (4th) 0.962 (5th) Clubman Quaife
3.454 (1st) 2.333 (2nd) 1.750 (3rd) 1.354 (4th) 0.972 (5th) Synchro Quaife
3.080 (1st) 2.150 (2nd) 1.350 (3rd) 1.050 (4th) 0.738 (5th) Andrewtech Automotive (PPG custom)
3.180 (1st) 1.870 (2nd) 1.320 (3rd) 0.950 (4th) 0.738 (5th) PPG SC dog
3.080 (1st) 2.150 (2nd) 1.500 (3rd) 1.050 (4th) 0.738 (5th) PPG HC dog
3.080 (1st) 1.870 (2nd) 1.320 (3rd) 0.950 (4th) 0.738 (5th) PPG SC synchro
3.180 (1st) 1.870 (2nd) 1.320 (3rd) 0.950 (4th) 0.738 (5th) PPG HC synchro
MRT’s gear ratios (.pdf document)

These are all the listed gear ratios for different manufacturers. Some manufacturers do not list gear ratios on their website, do not list them all, or offer custom options. Please consult with the manufacturer for their latest information.

What will my top speed, RPM @ 80 MPH be, etc. with a new gear set? You can figure this out with a high degree of precision using these two formats:
a. Web based format
b. Excel spreadsheet

What steps can I take to avoid transmission failure? There are many users of stock Subaru transmissions that have heavily modified vehicles. It goes without saying that when used with the proper shifting techniques, your transmission will enjoy a long and healthy life if you learn the quirks of your transmission and modify your shifting technique to promote a long and healthy life. The Shifting FAQ and the assistance of experienced local personnel should be able to provide assistance with proper shifting techniques.

Aside from proper shifting, use of the factory clutch or an organic clutch of similar design should ease driveline shock. The clutch was conceived to be a weak, mechanically adaptable link between the engine and the transmission to protect these more vital assemblies. Upgraded clutches on a stock transmission can accelerate failure. For more clutch/flywheel info view the Clutch & Flywheel FAQ.

To a certain degree, lowering your final drive will produce more mechanical advantage at the ring and pinion gears and less at the transmission (less stress on the gearset). This can be accomplished by a final drive ratio conversion or through using smaller than OEM 24.9″ circumference tires. This link contains calculators to determine tire heights and effective gear ratios for new tires. For example, a popular tire upgrade for the WRX is 50 series 16″ tire with a 24.1″ circumference. This equates to an effective final drive ratio of 4.03 over the OEM 3.90.

Another option is RWD conversion through DIY means or in the form of a purchased kit via, MRT, Rocket Rally, or Kingpin. Obviously this is not an option for true AWD lovers and it can create its own set of unique problems associated with additional stress to the rear driveline components. It can ease transmission stress as additional driveline forces get transmitted into tire smoke.

How much power can a gear set take? Shock load is the PRIME indication of when a gear set will fail. Though some manufacturers/vendors advertise HP ratings, those should be taken with a big grain of salt.

What causes a gear set to fail? Shock load. Shock load is the term used to describe any amount of drive line shock, though usually associated with extreme acceleration or traditional drag strip launches. It is an incalculable forum based on power times application of power time severity of application times about 900 other variables. While many manufacturers say that their gear set can withstand XXX HP or TQ, this is merely a general indication of its strength. Any gear set is subject to failure and the key component of that failure is the number of times a shock load occurs within that gear set.

While the exact number of shock loads before failure depends on the power and type of shock load, this is what most professional racings teams do to avoid transmission failure: Carefully document and run a new transmission to failure. This can be XXX uses, hours, or other means of accountability. Once failure occurs, subtract 10% from the accountability figure and use this figure as the replacement cycle. Obviously, this figure may then be modified or scheduled maintenance and inspections may occur periodically prior to the replacement cycle. Once a schedule is set, replacement occurs prior to failure. Many professional race teams report wonderful results using this methodology.

What is the cheapest transmission upgrade? An STi gear set (RA or non RA 5 speed set), Legacy GT gearset, or another OEM gear set would constitute the cheapest upgrades. Pricing for the STi RA and Non-RA gear sets is around $1300 depending on the retailer plus possible additional costs normally found during installation and applicable installation charges. A Legacy GT or an OEM complete gear set will be around $850. It is important to note that as of March of 2002 (build date) the Subaru 5MT swapped over to RA width gears. If your transmission code is TY754VN2AA you have the narrow gears. If you have transmission code TY754VN2BA you have the wider gears. So many 2002 and some 2003 (model year) users switching to newer gears would not only get new gears, but stronger gears. All gears available through Subaru are now the newer RA width.

What about 06+ WRX owners? Your final drive is 3.70 vs the previous year models’ 3.90. This in effect adds 6% more load to your gears vs. previous years. While it’s impossible to calculate this into the shock load formula mentioned above, it is noted that there are an increasing amount of 06+ owners with broken gears being seen here. So shift/drive kindly, investigate increasing your apparent final drive through smaller diameter tires, and temper your power modifications based on how soon you can afford to upgrade gears.

What is cryo treatment? Simply put, it is a process of freezing parts to -300° F to improve their properties. It is a “dry” process, during which the parts are never put in contact with the liquid nitrogen. The parts are cooled very slowly and then held at a temperature of about -300° F for anywhere from 24 to 36 hours, and then brought very slowly back to room temperature. Deep cryogenic tempering creates significant increases in abrasive wear resistance and durability. These improvements may be accompanied by increases in tensile strength, toughness, and stability coupled with the release of internal residual stresses. While cryogenic treatment is primarily used to improve the properties of the material, it can also provide stress relief, reductions in stress-relief cracking, improved surface finish, and improved machinability.

What is shot peening? Shot peening is a cold working process in which the surface of a part is bombarded with small spherical media called shot. Each piece of shot striking the material acts as a tiny peening hammer, imparting to the surface a small indentation or dimple. In order for the dimple to be created, the surface of the material must be yielded in tension. Below the surface, the material tries to restore its original shape, thereby producing below the dimple, a hemisphere of cold-worked material highly stressed in compression.

Nearly all fatigue and stress corrosion failures originate at the surface of a part. Further, it has been well established that cracks will not initiate or propagate in a compressively stressed zone. Since the overlapping dimples from shot peening create a uniform layer of compressive stress at metal surfaces, the process provides considerable increases in part life. Compressive stresses are beneficial in increasing resistance to fatigue failures, corrosion fatigue, stress corrosion cracking, hydrogen assisted cracking, fretting, galling and erosion caused by cavitation. The maximum compressive residual stress produced just below the surface of a part by shot peening is at least as great as one half the yield strength of the material being peened.

Shot peening increases the lifespan of treated metal components by ~20%.

How much are brand new, fully assembled 2005 OEM transmissions?
Ratios verified via SOA on 11/19/04 and all prices are retail with no discounts:
WRX transmission 32000AG970 $3111.92
3.454 (1st) 1.947 (2nd) 1.366 (3rd) 0.972 (4th) 0.738 (5th) WRX FD 3.90
(Front 3.9 center 1.1 rear 3.54)
RS transmission 32000AH000 $3111.92
3.454 (1st) 2.062 (2nd) 1.448 (3rd) 1.088 (4th) 0.780 (5th) RS FD 3.90
(Front 4.11 center 1.0 rear 4.11)
FXT transmission 32000AG820 $3111.92
3.454 (1st) 2.062 (2nd) 1.448 (3rd) 1.088 (4th) 0.780 (5th) FXT FD 4.444
(Front 4.44 center 1.0 rear 4.44)
Legacy GT transmission 32000AG780 $3111.92
3.166 (1st) 1.882 (2nd) 1.296 (3rd) 0.972 (4th) 0.738 (5th) Legacy GT FD 4.11
(Front 4.11 center 1.0 rear 4.11)
Outback XT
3.454 (1st) 1.947 (2nd) 1.366 (3rd) 0.972 (4th) 0.738 (5th) XT FD 4.444
(Front 4.44 center 1.0 rear 4.44)
STi transmission 32000AH150 $4994.83
3.636 (1st) 2.375 (2nd) 1.761 (3rd) 1.346 (4th) 0.971 (5th) 0.756 (6th) STi (USDM) FD 3.90
(Front 3.90 center 1.0 rear 3.90)
Total cost for 5 gears and the main shaft for a WRX transmission is $864.76. Broken down they are as follows: 1st $173.85, 2nd $147.22, 3rd & 4th $240.98, 5th $113.43, and shaft $189.28.

What’s involved with swapping from a 5MT to a 6MT? You will need to obtain and install the following components:
1. A complete 6MT transmission.
2. 6MT transmission mount.
3. 6MT clutch fork.
4. 6MT shift knob, 6MT shifter linkage, and 6MT shift boot.
5. The drive shaft from a 6MT or the drive shaft from any model automatic transmission equipped Subaru. The stock WRX 5MT drive shaft may also be modified (will need to be shortened) to fit as well.
6. New rear end options:
a. New ring and pinion gears to upgrade the stock WRX R160 rear differential to 3.90.
b. Convert the 6MT center differential from 1.0:1 to 1.1:1 and use the stock WRX R160 rear differential.
c. Swap out the stock WRX R160 rear differential to a stock STi R180 rear differential.
The real decision to a 6MT swap is the rear differential, as going with the R180, though the “better” choice, raises the costs significantly as you need to use the entire rear end consisting of the STi driveshaft, STi rear half shafts, Sti rear hubs, and STi rear discs to include the Brembo brakes. This will also require the use of 17″ wheels as well to accomidate the bigger brakes, which for some, may be an additional expense. As well, sells the parts that let you use R180 inner CV joints and the R160 outer CV joints if you want to use the R180 rear end and not swap over to the R180 hubs/brakes.

This thread provides additional 6MT swap help.

If I get an upgraded gear set, what other transmission related upgrades might I consider? Upgraded clutch, new flywheel, different final drive ratio, upgraded limited slip differentials, stainless steel clutch line, short shifter, shifter bushings (front, rear, pivot, linkage), rear diff bushings, subframe lockout bolts, outrigger bushings, and a new rear differential are all driveline components worthy of upgrade while your vehicle is down and the gear box is open.

How hard is it to install a gear set?
Professional installation, depending on your area, should run $600-$700 on a removed transmission. Removal/replacement from your vehicle should run an additional $450. Arguably the most important step in the process of upgrading your transmission is the final assembly. This is one vehicle modification that should only be accomplished by a transmission professional with a clear understanding of Subaru transmissions and special techniques and instructions that come with most gear sets. Additionally, for correct installation, the technician needs the Subaru Factory Service Manuals and specialized Subaru use only transmission tools for perfect alignment. If the shop does not have these items, find a place that does.

Are there any hidden costs with a transmission installation?
Yes. While the gear box is open, the technician may require/recommend additional parts to be installed. Some of these additional expenses can be figured prior to installation, some may crop up once the transmission is opened. Some gear sets may need additional parts as well. For example, some dog box transmissions should/must have new shifting forks or a shifter interlock. These parts can total as much as $1000. Total cost depends on your gear set and manufacturer/installer recommendations.

What questions should I ask of a gear set manufacturer or retailer?
1. What gear ratios do you offer?
2. Do you offer custom ratios or custom gear sets?
3. Are there any modifications to the case in order for your gear set to fit?
4. What is the warranty on your gear sets?
5. What other recommendations do you have?
6. How much “oops money” should I factor into my purchase in case other parts are needed?

What are common causes of transmission failures on vehicles with upgraded gear sets/transmissions? While there is no perfect answer to this, searching for failure issues can lead you to the following conclusions:
a. Installation errors.
b. Lack of recommended upgrades (broken stock shifting forks).
c. Driver inexperience.

Any other good articles on gear sets or related information? These articles may provide additional helpful information:

Subaru Barking Box
PAR’s transmission FAQ
Upgraded rear differential
Upgraded final drive ratio
Mike Shield’s transmission notes
.pdf about shot peening

Editors Note

This post was created because I wasn’t able to find a good transmission FAQ. I came up with the text based on LOTS of searching here. Upon reading this you should have an idea of whether a transmission upgrade best suits your needs or not. The manufacturer is up to you.

My thanks to Brett Middleton from MRT, Geoff from CTI-Distributing, Paul Guard (gearguy) from Guard Transmissions, the Metal Improvement Company, and most importantly, Andrew Yates from for providing valuable assistance in the formulation of this FAQ and for shedding some light on the world of transmissions.

If you find an error in this FAQ, please PM me with factual details and I will update this post. Responses such as, “I have XXX’s gears and they’re great!” or “XXX’s gears broke after 1 month” are not appreciated here, that is what the Car Parts Review Forum is for.

One Response to “Transmission FAQ”

  1. I’m looking at a subie front wheel drive tranny. Is it possible to flip the ring and pinion around in order to run the trannsmission in a rear engine car? I know it can be done a VW transmissions. I disagree on your tranny flex theory. You run enough HP through that case it will flex to the point where the gears will skip. I’ve been running VW Bus cases in offoad racing for years and have seen my share of transmission breaking because of flex. The tranny is only built to take so much HP and torque. After a certain point the housing will flex under the pressure. On that note, do you know how much abuse the Subie tranny will take.

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