A key component of the WEVO 5-speed transmission kit for Porche 356 is the swing-axle differential. This bespoke WEVO part is necessary to marry together the dimensions of the larger crownwheel gear from the 901-series transmission and the swing-axle rear suspension design in your 356 chassis.
WEVO was able to incorporate several technical features that enhance durability and ease of assembly in the clean-sheet design for this part.
356 Taper Roller Bearing Configuration
WEVO’s 356 5-speed differential runs on a pair of opposed taper roller bearings. All original 356 transmissions used a pair of ball bearings. Subsequently, when Porsche introduced the 901 series, they evolved the design to use taper roller bearings that allow for simple pre-load adjustment and excellent load capacity. We adapt the taper roller bearing configuration to our swing-axle differential design, as these bearings offer the greatest set-up freedom. Modern Porsche technicians are most experienced with this set-up process.
Each WEVO 356 5-speed differential is built from new parts. The four spider gears and two bevel gears are new parts sourced directly from Volkswagen. As the applicable Porsche parts are no longer available, these dimensionally-identical VW items are the only option for brand new, OE-quality components. The new parts are subjected to REM isotropic superfinishing for reduced friction.
Upgraded Spider Gears
The second key feature of WEVO’s 356 5-speed swing-axle differential, is its four spider gears. A typical open differential design uses elements known as ‘spider gears’: small bevel spur gears that are essential to transmit the torque of the engine to the wheels. The spider gears are a common area of failure on high-powered cars, cars with wider tyres and off-road racers. The original Porsche 356 differential has just two spider gears and, while not considered the weakest link in Porsche 356 transmissions, with the increased power capacity of the 901-series gearsets in the 356 5-speed, WEVO considered four spider gears to be essential in this transmission design.
Externally Accessible Snap Rings
The third technical feature in the one piece differential housing design with large snap-rings retaining the bevel gears. The original 356 differential housing is a 2 piece design and requires removal from the transmission and complete disassembly of the differential unit to be able to inspect, service, remove or install the axles, fulcrum plates and bevel gears. You will typically see a 356 transmission stored or transported with the axle tubes mounted and the axles installed. It makes a large and vulnerable package. We avoid this inconvenience with the externally accessible snap rings.
For several years after Porsche ended its development of the 356 model, VW continued to use the Porsche swing-axle suspension design on their VW Bus and Beetle models. The last iteration of those parts for the sturdy VW Bus used a larger carrier bearing and ‘snap ring’ design, to retain the bevel gears inside the differential. WEVO has mimicked that successful design in the packaging of the 356 5-speed differential unit, as this allows for axles, fulcrum plates and bevel gears all to be removed and inspected, serviced or replaced with the transmission installed in the car and the differential installed in the transmission. The process is so simple that even the oil does not need to be drained (although a small amount may run out once the axle tubes are removed).
The added bonus from the snap ring design is the convenience of allowing the transmission to be shipped or stored in the most compact manner, with the axles removed from the fully-assembled transmission. No post-delivery disassembly and no special skills are required to install the axles, just the pair of sturdy snap-ring pliers that come with the kit. Once a WEVO 356 5-speed transmission build has been finished on the bench and all checks completed, the fully-built transmission is shipped to customers in a modest shipping case. Owners may then install the axles and axle tubes with the existing brakes and so on that are parts of your 356.
Differential Housing Manufacture
The differential housing is made from a heat-treated steel alloy and is light and sturdy. The crownwheel gear is fastened by twelve original equipment Porsche bolts. The bolts have provision for lock tabs and there is clearance inside the final drive housing to install the lock tabs.
The carrier bearings require shims to correctly set the preload of the carrier bearings and then to manipulate the backlash of the crownwheel and pinion setup. The actual shim values are unknown until the technician capable of performing these critical adjustments is completing the work. A full range of shims are on our shelves, as these are unique to the 356 5-speed and manufactured specifically for this project.
Shim Voucher System
As a mix of shims is required to set bearing preload and CWP backlash, WEVO is experimenting with a shim voucher system, where your kit is supplied with an excess of shims and when the unused parts are returned, we apply a credit to your account for future purchases.
By working directly with a WEVO-accredited 356 5-speed builder, you will find they are equipped with the shim inventory and special set-up tools that are part of the accreditation process.
Note that your Porsche 356 5-speed transmission kit is shipped with the differential unit fully assembled, with the spider gears installed and the thrust shims selected and installed for the correct backlash on the bevel gears. These bevel gears and corresponding shim should not be mixed left-to-right.
Re-using your 356 Axles
You will be re-using the existing axles from your Porsche 356, so the drive spades must be checked for scoring and galling once the axles are removed. This is common on all 356 axles, but there is a limit to what is sensible to re-use. Working with a hand stone and other fine abrasives, many axles can be improved for continued use. As new axles are still available from Porsche, Sway-A-Way and European sources, those options are left for you to consider.
The last key parts of the differential are the fulcrum plates. These small crescent shaped parts are an important part of the rudimentary universal joint created inside the socket of the bevel gears. The drive blade on the axle slides between the fulcrum plates, which, in turn, can articulate in the bevel gear socket: an imaginative design by Porsche. Every Porsche 356 and VW Beetle built before 1968 (i.e. millions of cars) employ this novel feature and so it continues in the 356 5-speed.
You will need to make a decision to either re-use your existing fulcrum plates or buy new parts. With new Porsche fulcrum plates currently running close to $1,000 for the 4 pieces, we leave that decision to the customer. New fulcrum plates are not included in the kit, but we can supply them if you chose. The Porsche part # is 690 321 232 00. The parts being supplied by Porsche in 2015 are quite different to those found in original 356 differentials. The new parts are a bronze alloy of some type, gold/bronze in colour, with oil transfer grooves cut into the flat face contacting the drive blade on the axles.
Old fulcrum plates are often scored and galled. Always consider that you are potentially putting the new parts in your kit at risk by electing to continue using marginalised parts from your old transmission/axle pairing.