Choosing a Transaxle for your 944
You might want to swap to an Audi transaxle for reliability, to pair with higher torque output engine, for upgradeability, for different gear ratios or simply as a cheaper alternative to rebuilding a 944 transaxle. Selecting the right option can involve many factors so its good to think about what you want from the conversion before going into the following details.
There are 4 main contenders that are capable and reliable (all 6 speed)
- 01E – The well proven wonder transaxle that most will have at least heard of
- 0A2 – The newer, more modern and lighter version of the 01E
- 01X – A transaxle of the same generation as the 0A2 but with many different gear ratio sets and plenty of features suiting those with a more refined and road focused car
- G87.20/G87.21 – The Porsche rebranded version of the 0A2 from the 6 speed 987
Please note that the more modern transaxles differentiate between all wheel drive (AWD) and front wheel drive (FWD) variants with different gearbox codes but the 01E code is used for both. Also note most importantly that the 01E AWD gearbox is not the same and any power figures or legendary status attached to the FWD variant does not translate across. I do not recommend AWD variants of any gearbox be used for your conversion and all references from here onward will be for FWD variants only. AWD transaxles are simply not as strong. There is also a 5 speed variant of the 01E which will not be covered and is assumed to be inferior to the 6 speed
There are Audi SSP (Self Study Program) documents for lots of different sub assemblies. One of them covers the 0A2 and 01X and compares them to the previous generation 01E. Its an interesting read but I’ll summarise the changes below anyway
The document can be found here: SSP325 A6 Assemblies
Cost
Depending on where in the world you are located, some can be easier or cheaper to get than others but even shipping from other countries you will find the prices to be quite cheap for all options apart from the G87 which comes with a hefty Porsche tax. For those in the UK and Europe, it’s possible to get transaxles for as little as £50 with enough patience but with a budget of £300 you can generally get any of the Audi options straight away. I will be able to source transaxles for those that want me to.
I don’t believe the G87 is a good choice because it is very expensive and not functionally different to the 0A2 apart from ratios. It is available used in most of the world though.
Gear Ratios
Below are what I believe to be the majority of ratios available for each transaxle. There are often multiple gearbox codes for each ratio but some of the headings have a code included in brackets.
The input spline of the G87 is orange because it has not been verified yet and if it is different, which I highly doubt then I will not be supporting it. Reverse engineering the spline profiles and getting the fit right was expensive and time consuming.
LSD Options
Not all transaxles are equal here. The 01E has a motorsport pedigree and there are tons of options compared to the newer transaxles. That also means some of the cheaper LSD manufacturers like Quaife or Gripper make compatible parts for 01E
| 01E | 0A2 | 01X | G87 |
| Lots of options for clutch type and helical/gear/torsen type | Drexler clutch type | Drexler clutch type seems to be hinted in some places but it’s not clear if this is actually available | There is a factory option but it’s not very good so more worthwhile sourcing aftermarket. OS Giken and Drexler offer clutch type and there are loads of sources for helical/gear/torsen type |
Power and Torque Handling
Power figures are often used to give ratings for components in the automotive world but when thinking about transaxles it’s the torque that matters. A diesel engine will produce much higher torque figures and probably lower power than a similar displacement petrol engine for example. I’ll stick to torque figures for the rest of this section
The torque that each transaxle can take is quite hard to quantify and with few anecdotal examples of the 0A2,01X anG87 being used in very high power/torque applications it’s hard to make claims about any of them or indeed rank them all against each other. I will cover the what is known below that will help give an idea though
There are some numbers we can pull from the Audi SSP document to get started with. The official torque rating for the 01E and 0A2 is 450Nm and the 01X is 330Nm
The 01E in a 944 application is known to handle 1200Nm (measured at the wheels) for drifting. See https://www.instagram.com/f2iceland/ for the car. At these power levels, the 01E has proven not to be the weakest link in the system after twisting the torque tube driveshaft and snapping wheel hub flanges
Not all 01E transaxles are created equal and over its long production span there were updates. Transaxles from 1996 and later got a wider 1st gear (26mm vs 22mm) and there were different synchromesh updates throughout production. The 968 variant of the 01E used 22mm 1st gear for reference. It is important to note that there is some speculation that variants of the 01E used behind the V6 TDI engines may have shorter input shafts (said to be 0.5″ shorter). I currently believe the difference is only in the length of the tip of the input shaft and will not matter for the 944 application with my coupler. i will confirm this as soon as i can. Additionally very late years of the 01E were produced by VW instead of Getrag and commonly suffer from a pinion bearing issue causing a whining noise. One of these later transaxle codes is FRK. Although, the replacement bearing is much cheaper than buying all of the upgraded synchros for an older transaxle so it’s still a good option.
The 0A2 is theoretically as strong or stronger than the 01E because it has larger diameter gears. The larger diameter reduces the force on the gear teeth and means they are less likely to shear off. However, the 01e has a steel casing and the 0A2 has an aluminium casing so it’s not possible the call it
The 01X is in theory a lower torque gearbox but Bruce at Dirty MArtini Racing is proving differently by drag racing a 924 (https://www.instagram.com/dirty_martini_porsche_924/). He has uniquely tried many different 01E and 0A2 gearboxes and more recently an 01X behind his big turbo 1.8t engine. The 01X has shown to be more resilient to drag racing and high RPM launching on sticky tyres than the other two. This isn’t necessarily overall gear strength as some of the previous transaxles suffered synchromesh failures. He has snapped off gear teeth and broken gears in the previous gearboxes so it’s a good test with more launches to come in this year’s season
Synchromeshes
The most important thing for 944 owners to consider is the synchromeshes for 1st and mainly 2nd gear because it gets the most use. Due to the long torque tube shaft and the gearbox coupler, the 944 has much higher rotational inertia on the input shaft than most other cars. For example in another rear wheel drive application like a BMW, it is only the weight of the clutch that the synchromeshes have to work with outside of the gearbox.
In short: 01E, 0A2 and G87 had synchro issues that were later sorted out. The updated parts are available and can be retrofitted though. 01X doesn’t seem to have the same issues
My recommendation on the following is to run what you get until it’s an issue but be aware that if you are having problems there is a solution.
In depth: There are different synchromesh designs and different materials. They can be broadly split into single, double and triple cone designs and then categorised by the friction material. It is safe to assume that the higher number of cones and therefore surface area for friction increases shifting power but also speed.
The 01E has the oldest and most basic single cone synchros. These don’t offer tons of power when synchronising the input shaft with the output shaft and it can be hard to shift gears with a big mismatch in revs. Audi did a factory update from the standard friction material to a carbon material and also changed the engagement angle which improves shifting and longevity. There is also an aftermarket option from JHM which may or may not be better than Audi but still needs the updated Audi shift collar to work. The kit is listed for AWD transaxles but it is assumed to work with FWD also. The parts are a drop in replacement if your transmission doesn’t already have them and the part number for the kit is 01E 398 270. According to unverified sources, the changeover date for the synchros is believed to be 01/2002. There is a chance this job may need to be done if purchasing an earlier 01E transaxle but afterwards should be sufficient for reliable operation in a 944. On the older 01E, shifts are likely to be a bit slower than 0A2 or 01X and you may find the synchros wear out quickly when shifting fast at high RPM. You can see a lot of chat about this in Audi forums: Search for 0A3 vs 01E for the biggest sample size on this issue.
The 0A2 (and G87 – most of the G87 internals have 0A2 part numbers so im assuming its the same inside) got triple cone sychros for 1st and 2nd gear with double cone for 3rd-6th and also reverse. There are however issues with the OEM triple cone synchros for 1st and mainly 2nd gear. You can find this documented a lot on 987 forums but also on audi forums. Again, search 0A3 in place of 0A2 to increase your number of hits. Audi did a well reported update on the 2nd gear for the G87 (similar gearbox) and I assume also the 0A2 which solves the problem. There are various part numbers for the 0A2 synchros with the latest having carbon on all friction surfaces (part no: 0A2311283) so i assume this is the updated part. GBox also sell synchros for the G87 which may or may not be just 0A2 parts with a porsche label but they appear not to have the carbon friction material. Its likely that even without updating the synchros in this gearbox you will only have issues if its had tons of miles or you are shifting aggressively
The 01X got triple cone 1st, double cone 2nd and single cone 3rd – 6th and reverse. This could be the key to its reliability in drag racing… less moving parts. The sample pool is much smaller for 01X and it’s generally not used in higher power cars apart from recent interest in the GT40 replica community. This could also explain the lack of failures but The Dirty Martini Racing 924 is having great success with it where the 0A2 Synchros have failed
Installation Considerations
Both early and late cars
Transaxle mounts are the only mechanical part of the kit to be specific to each transaxle so changing later on will only be possible with new mounts or modifying the supplied ones. There will be 3 variants for: 01E, 01x and the 0A2 and G87 will share a mount
Due to the Audi transaxle’s input shaft being a smaller diameter than the 944 torque tube spline, the coupler that joins them cannot slide onto the torque tube for removal of the transaxle. If you haven’t removed a 944 transaxle before, the coupler unbolts, slides forwards and allows the transaxle to drop down with relative ease. The Audi transaxle installation will be more involved but thankfully won’t be happening often given their strength. Installation can be done by dropping the rear subframe and allowing the torque tube to pivot down giving enough room to mate the transaxle and torque tube. Alternatively it may be possible to avoid this by making clearance in the 944 body for the transaxle to slide backwards. This is likely to involve chopping out the majority of the spare wheel well but i haven’t been able to verify this yet due to all of my current testers having cut out the whole boot floor previously.
In addition to the above, the 0A2, 01X and G87 transaxles are longer than the 944 transaxle and will need the spare wheel well modifying anyway. The 01E is the same length as the 944 Transaxle so can be installed without any body modifications.
All the transaxles bolt to the 944 torque tube with 4 bolts. On some transaxles the original full size bolt may not fit on one of the locations and a smaller bolt needs to be used but this hasn’t been an issue for anyone testing. You could of course modify the holes to fit a larger bolt. From memory, you will be fitting an M8 bolt in place of an M12 but I will need to check this.
Holes will need to be drilled into the tunnel area to mount the gear shifter. It is likely to be 4 holes close to the opening so no trim will need to be removed but is not set at this stage. Installation will be from the top and not require you to drop the torque tube but you will need to remove the long shift rod while the transmission is out. There will be a plastic trim to go with the shifter that will be early/late specific and potentially an option for those with no centre console.
Early cars only
There are no special considerations on the early cars. The speedometer is driven front the front wheels so no need for any speedo wiring parts and the kit uses the factory transmission mounting locations.
The axles for the early and late cars will be different lengths due to the different wheel hub offsets of the cars.
Late cars only
The single transmission mount of the late cars is a poor design and allows the transaxle to swing under acceleration. Especially a worn out old one. This causes the CV to bind and breaks the CV but generally takes out the axle too. The kit will be supplied with an additional piece of steelwork for the later cars that will need to be welded to the crossmember. This will provide two mounting locations in the same place as the early cars for a more robust mount. The crossmember is removable and can be taken to a welder if needed or the car can be reverted back to stock by purchasing another crossmember. There will be instructions and alignment features on the part for aligning before welding.
The late car has a different fuel tank to the early car and there can be some interference with some of the Audi transaxles. On the weld in mount, I have provisions for a second mounting position that is offset enough to avoid interference so that any transaxle can be used without issue. This will mean the torque tube is no longer running perfectly down the centre line of the car for some. This shouldn’t be an issue for the engine mounts as the 20mm at the rear only translates to a very small amount at the engine mount and well within it’s tolerance. The 01E can be mounted centrally if an insignificant part of it’s casing is trimmed off. The 0A2, 01X and G87 will need to be mounted 20mm to the side.
The electronic speed sensor on late cars is mounted in the transaxle and only the 01E has provisions for a sensor. A small electrical adapter will be needed to convert the 01E sensor to the 944 harness. For the 0A2, 01X and G87 an external sensor will be needed. A trigger ring for this sensor is incorporated into the CV adapters that are supplied with my kit so all that is needed is a cheap sensor and a mount which I can supply for those that need them.
The axles for the early and late cars will be different lengths due to the different wheel hub offsets of the cars.
Overview of differences
01E
- Lots of race car upgrade options for LSD and others that aren’t available for the others like dog gears, straight cut gears, oil coolers etc
- Not as refined and harder to shift gears especially at high RPM differential
- Least fragile shifting mechanism (search detent issues with 0a2 which are probably present with 01x also but low sample size on forums)
- Can be mounted without modifying spare wheel well if desired
- Can be mounted centrally in late car (not a concern for early car)
01X
- Very refined shifting for reduced input force proven on drag strip
- The most gear ratio sets to choose from
- Vibration transmitted to shifter should be negligible compared to 01E
- More efficient compared to 01E so uses less oil and doesn’t need an oil cooler where the 01e might do
- Better targeted oil system for gears than 01E
- Potentially lighter than 01E
0A2
- Theoretically can handle the most power and feels the most refined with largest gears and most advanced synchromeshes
- Similar to the 01X
- More efficient so doesn’t need an oil cooler where the 01e might do
- Vibration transmitted to shifter should be negligible compared to 01E
- Refined shifter feel
- Potentially lighter than 01e
- Axle output flanges are lower relative to the input shaft so allows more lift for those doing offroad builds
- Potential issue with 2nd gear detents (read up on forums)
- Longest ratio set option of all transaxles