THE TRANSWORKS 091+ TRANSAXLE IS NOW AVAILABLE!

The VW 091 bus transaxle has always been the best platform from which to build a VW-based high performance transaxle. Taking advantage of the availability of off the shelf parts, such as a super-diff, billet chromoly diff cover, Weddle gears, and Weddle 4.57 ring & pinion, an experienced builder is able to build a unit that is able to withstand up to around 300hp, depending on how the car is driven and how much it weighs. This means that once a builder has reached the highest level of competence possible, his transaxles are as good as anyone else’s with that level of competence, but no better. In other words, it doesn’t much matter where you have your transaxle built, because as long as your builder is capable of assembling the same collection of off the shelf parts that are available to everyone, the product will be the same. Some builders will try to convince you that they have “secret tricks” that make their product better. We prefer “engineering” and “solutions to problems”. There are no tricks or secrets here, only innovations. We looked at the 091 transaxles that we and everyone else were building and decided that there were some improvements that could be made. Our new 091+ transaxle has several modifications and improvements that can’t be found anywhere else. In time these are sure to be adopted by others, just as we avail ourselves of the innovations made by others in the past. We didn’t invent the super-diff, but we surely wouldn’t build a performance transaxle without one. At this point in time this is the absolutely toughest VW-based transaxle there is, and it can’t be bought anywhere else. Read on for a complete description and photos of all of these new improvements.

HEAVY-DUTY ALUMINUM INTERMEDIATE HOUSING

The intermediate housing is a critical part of the 091 case. The entire transmission section of the transaxle is built into this housing, and then installed into the main case as an assembly. The VW bus was a low-end economy car, so light weight and low cost were the most important factors when making the original castings. Strength and accuracy were secondary. After 30+ years of use and thousands upon thousands of heatings and coolings they experience metal fatigue, corrosion, and other issues. The pinion and mainshaft bearing bores are seldom round or in the right location anymore on a used housing, and the shift rail bores are always  worn out and need to have bushings installed. The original castings need to be machined to accommodate a lower 4^th gear, leaving a thin, weak area. Our new aluminum casting addresses all of these issues and then some. The aluminum is a stronger, more rigid material. We use a larger mainshaft bearing bore diameter, allowing the use of a larger mainshaft bearing, the same one used on the MD4-2D Mendeola. This bearing is rated for much higher radial and thrust loads than the standard VW bearing. We also added hard points for mounting, eliminating the need for a nose cone mount or external steel plate mount.
The new housing will accept the lowest 4^th gears made for the 091 with no clearance issues.

BILLET STEEL BEARING RETAINER

The larger mainshaft bearing we use on the 091+ projects above the surface of the intermediate housing. In the stock VW design, the bearing is flush with the surface, and the nose cone prevents the bearing from being pushed out of it’s bore by thrust loads. That wasn’t such a good idea even in a stock application because the bearing tended to wear it’s way into the surface of the soft magnesium nose cone. Using a new aluminum nose cone and an aftermarket thin steel plate is an adequate fix for this problem with the VW bearing, but our bearing extends past the housing surface, so we needed to design something new. Our new retainer encapsulates and retains the bearing very effectively, and it also replaces the stock shuttle linkage bracket. The stock bracket (shown next to our retainer) is another weak link, even in a stock application. It supports a pin, which carries a shuttle linkage to the shift rails. The stock part has a tendency to flex, bend, and break. The standard fix for this is to box in the stock bracket, and that works fine strength-wise, but doesn’t address the worn out pin bores that the 30+ year original part always has. With the geometry of the VW shifting system being what it is, a little bit of slop in those bores adds up to a lot of slop at the shifter. In our retainer those bores are precision reamed into substantially thicker steel than the stock stamped steel bracket.
 

BRASS LOAD BOLT

Load bolts to prevent ring gear deflection under load have been around since forever on giant truck rear ends with 13” ring gears. What the load bolt does is kind of backstop the ring gear to prevent it from flexing under heavy loads. You wouldn’t think that a heavy steel ring gear would be able to flex much, but it does flex a surprising amount during heavy loads. While it is loaded and flexed, the ring gear is not maintaining the proper mesh relationship with the pinion gear, and this causes ring & pinion wear and breakage. Mendeola transaxles have always used a ¾” brass load bolt, and they are very effective. When servicing Mendeola transaxles we always notice the brass deposits on the back of the ring gear, proving that the load bolt is absorbing quite a load and preventing ring gear flex. With all of the aftermarket gears and parts now available for the 091 it is pretty easy to build a gearbox having the ring & pinion as the weakest link. The outstanding quality of Weddle’s 4.57 ring & pinions have greatly strengthened this weak link, but it remains the weakest link. It is not physically possible to install a larger diameter ring gear into an 091 case, so that leaves the load bolt as the only possible improvement to strengthen the weakest link, making it imperative.

          Setting up the 091 case for the load bolt was fairly simple. The spot where it needs to be happens to be right between 2 deep ribs in the case, so all we have to do is weld up the area between the ribs, machine it to shape, and drill and tap it. This gives us a hard point with an 1-3/4” deep thread for a ¾” load bolt. The 091 ring gear does not extend beyond the edge of the differential housing, as it does on a Mendeola, and with the ring gear bolts in the way there is no flat contact area for the load bolt. We solved this problem with a steel friction ring that attaches to the diff cover, covering the bolt heads and providing a flat friction surface.

FLANGE SUPPORT BEARINGS

A stock VW bus has 3-4 inches of suspension travel and a nearly horizontal axle angle. This doesn’t put a lot of side load on the output shafts, but stock VW busses still had a tendency to eventually wear out cv flanges and differential housings and covers. Modern sand cars with 22+ inches of suspension travel put a much higher side load on the output shafts, and increasing the cv joint diameter from the stock 100mm to 930 cv joints (110mm) doesn’t increase the side load leverage by 10%, it increases exponentially to a much higher level. People tend to think they are not seeing the effects of this side load if they are not seeing worn out cv flanges , differential housings, or differential covers. The fact is that is that broken ring & pinion gears are often attributable to this force, and the reason that we don’t often see worn out cv flanges, differential covers, and differential housings is that the high performance aftermarket versions of these parts that we all use can take a lot more abuse than the stock parts. Even though the differential housing runs in fairly large loaded, opposed, tapered roller bearings, it is constantly deflected from it’s center line by suspension loads. These forces are seen as short, momentary shock loads which are constantly changing the mesh relationship between the ring and pinion gears, causing a hammering effect on the gear teeth. The 091+ has modified side covers and a bearing/seal housing that allows the installation of ball bearings that support the cv flanges. These bearings cause suspension side loads to be transferred to and absorbed by the case instead of the differential housing, which helps prevent ring and pinion gear breakage.

INPUT SHAFT BEARING

One of the failing points of the stock 091 transaxle is the center mainshaft bearing. It is a fairly small shell needle bearing, and along with the tiny pilot needle bearing on the other end of the input shaft it is expected to absorb the radial and axial loads generated by the rotating mass of the clutch disc. This bearing often wears out prematurely, and when it fails it often destroys the main case. We thought it would not be a good idea to install a larger bearing, because there is not much metal between the mainshaft and pinion bores as it is, and with a larger bearing bore the case may tend to crack at that point. On the 091+ we perform a minor od grinding operation on the input shaft and bore the bell housing, allowing us to install a small ball bearing in the bell housing. This eases the load on both the center mainshaft bearing and pilot bearing, and extends center mainshaft bearing life.