Those of us who own these cars also get involved with repairs. Since most of our cars are not pristine “trailer queens,” we look for used parts as either replacements or upgrades. Transaxles can be very expensive to rebuild – $2,000 or more. So finding transaxles on the used market is normally what we do.
There have been a variety of transaxles used in the 924/944/924S/968 series. Understanding them helps to understand what to do when you need to replace yours – getting the right one that will work with your car. Replacing the transaxle is not an easy task, and you don’t want to have to do it twice. Note – I will not talk about the automatics here, only the manuals.)
The early car – the 924 – had three different series of transaxles. The earliest transaxles were four-speed gearboxes that utilized a 20mm input shaft. When Porsche went to a five-speed gearbox, they installed what become known as the “snailshell” transaxle – the G31. While the other transaxles were sourced from Audi, the snailshell G31 was a Porsche unit. The snailshell was used in the 1979 924, then in some of the 924 Turbos, but generally replaced with the five-speed 016 Audi transaxle in 1980 to 1982.
The primary difference between the 924 NA and 931 gearboxes was the input shaft. The earlier NA cars have a 20mm input shaft while the 931 had a 25mm input shaft. That 25mm input shaft carried over to the 944. This means that the driveshaft tube (torque tube) in the early cars has a 20mm driveshaft while the 931 and 944 have a 25mm shaft. Of course, that carries over to the flywheel, clutch, and other driveline parts, including the starter.
As a transitional model, the 931 utilizes a lot more 944 parts in the driveline than you may realize. The 931 was raced by the factory, so they built stronger components to handle the higher power of the race-prepped turbo engine; of course, this spilled into the development of the 944.
The 1979 924 “Snailshell” G31 gearbox was an interesting design. It put the actual transmission in front of the differential, although both were housed together. The Audi transaxles put the gearbox behind the differential – the power goes past the differential into the gearbox, then back forward into the diff. By placing the gearbox in front of the differential, the weight of all those spinning gears was in front of the diff, thus inside the wheelbase instead of behind the rear axle. Smart thinking. However, the G31 was mounted to two arms attached to the rear suspension instead of the Audi mounting to the underside of the body. And the G31 uses a two-rod shifter system instead of the Audi one-rod shift mechanism. The torque tube is also quite different. So if you want to change over to the G31, you need to change all that stuff. (I did it once about thirty years ago, and would not do it again!)
With the introduction of the 944 in 1983, the Audi 016 gearbox was adopted going forward. Over the years, improvements were made, but the basic gearbox remained the same. Limited slip differentials were optional, and the turbo gearboxes were reinforced in many areas to help handle the power. One version of the turbo transaxle got an external cooler.
Little known fact – the 016 Audi transaxles have a 3.89 rear gear – the rear end ratio. However, the 016 Audi transaxles in the earlier 931 almost all have 4:11 rear ratios. These 4:11 gears will install into any transaxles with the 3.89 ratios, giving the racers an option. But beware – some racing series, including 944 Cup, do not allow non-stock ratios. The transmission can be identified with “016/9” stamped on the top of the bell housing.
Another note for the 924S – their transaxles are identical to the same-year 944 with one exception – the 924S gearbox has a .730 fifth gear while the 944 has a .829 fifth. For racers, this makes the 924S ratios much more desirable. The “urban legend” is that during development, the lighter and more aerodynamic 924S narrow body was actually faster in top speed than the 944 – and that was not acceptable. The fifth gear ratio was changed to slow it down. True? Who knows, but it’s a great story.
When the 944 Series II cars debuted in 1985-and-a-half, they all had plastic gas tanks with a higher capacity. This necessitated a change in how the transaxle was mounted in the car. The early cars, including the 924 and the 924S (but excluding the ’79 G31 trans) were mounted in the car with two “ears” mounting it to the underside of the body. With the Series II cars, the plastic tank made it necessary to bolt in a “bow” and hang the transmission from it on a “center mount.” Series II gearboxes cannot be easily adapted to early cars; the older “ears” mounts will not bolt to the transmission, and putting a plastic tank with the proper transmission mounting can be a challenge. If this is something that you are planning, do your research first. It is not a bolt-in.
There is another urban legend out there saying that all Porsche transaxles are designed to handle at least twice the power and torque of the power plant originally installed. Truth or fiction? Who knows. We do know that as long as transaxles are treated to proper maintenance, they can last a long time. In all the 924, 944 and 924S cars that I have owned, I have come across only two bad gearboxes. They both presented themselves with noises like marbles in a tin can. Those of us who tear apart parts cars also know that used transaxles are out there because they are rarely torn up or unusable. With the price of a complete rebuild, stuffing a used box in your car is almost always the right decision.
Here is a comparison chart that I have found to be very useful in understanding these things…PorscheTrans comparison revised 2-18
This link to Clarks Garage has a lot of great transaxle identification info. https://www.clarks-garage.com/shop-manual/trans-04.htm
Please chime in with more info on this topic!!
Kevin Duffy is an Associate Professor of Criminal Justice at Daytona State College in Florida and a dedicated car guy. He divides his time between teaching criminal justice topics in the online environment and working on/driving cars, particularly Porsches. Kevin is one of the principals in InspiringLifeOver50.com.