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Our philosophy is that transaxles should work so smoothly and quietly that they are easily forgotten.
AT RIGHT: This is a split-case transaxle we rebuilt in 1991. Both Porsche and VW split-case transxles are significantly more challenging than later tunnel type transaxles. Simply, disassembly / reassembly are far more challenging. This transaxle served for over 20K miles of flawless service before we lost track of it following a sale in the late naughts.
Of course, as already articulated on our main web page, we have vendors we can use to rebuild transaxles for the cars we serve, yet we also rebuild these ourselves, have significant expertise, and unique approaches and tools that nobody else uses to provide a superior result. Here we describe what we do.
We are happy to share our techniques because we know that discerning customers go with knowledge-leaders.
AT RIGHT: This image is "Figure 79" from the 356 B / C workshop manual. Here we see the Porsche factory's strategy for removing the differential! ACK! NO! This must be a primary cause of why so many differentials are cracked! Smacking the axle end with a hammer puts a shock load on the differential carrier at the spider gear cross shaft. ...We do it more intelligently!...
Here's what you can find here:
Unfortunately, the differential carrier is iron, not steel, and as such it's more brittle than steel and these parts are famous for cracking. Yet the factory calls for literally hammering on the end of an axle to drive the differential out of one of the side covers which puts all the load of said hammering on the spider gear shaft, which in turn directly bears on two vulnerable spots of the differential. In our view, this technique is a prime reason why differential carriers are often cracked, especially since multiple assemblies may be required to complete a rebuild. Here, on this page, we show you how we do it better.
AT RIGHT: Here are two 6-bolt differential carriers used in Porsche 356 and split-case VW transaxles. The one on the left is "uncut", and the one on the left has been reduced in diameter to clearance the input shaft used on some 356 units. This is discussed more below.
A second reason why differentials are often cracked has to do with the rather poor choice - by modern standards - of retaining the spider gear cross-shaft. The original technique was the use of a solid drift-pin that's peined into place. Less skilled mechanics often crack the differential carrier when performing the peining. Sometimes silly people try to drift out a fat ended pin through the carrier, cracking it. Instead, comptent shops today install a roll-pin of similar size. These roll-pins are basically a circular spring of similar diameter and length to the original drift-pin and whose un-sprung outside diameter is larger than the original drift pin and whose compressed diameter is smaller. So, compressed, it slides in easily and once released, it stays all on its own - no peining necessary.
BELOW, LEFT & RIGHT: Here, an axle assembly is being pushed out of the case using our special tools, described below. Notice the coupling nuts threaded into the case studs that protrude through the side cover. The M8 bolts running through the thick metal plate simply support the nuts that are then turned and thereby push the piece of tubing that just fits inside the side-bearings, but not the differential carrier. And so, the axle assembly comes out the other side. The other holes are there for other operations seen below and the notch visible on the edge provides clearance for the much longer axle-tube mounting studs that also serve for mounting the bowden tube support on the other side.
As noted above, the factory approach to removing the differential from either side bearing was to pound on an axle end with a lead or copper hammer. However, many shops don't have lead or copper hammers and, even if they do, their removal process shocks the differential carrier and cracks it. Instead, we have created our own tools that gently push the pieces apart - tools any competent shop can make based on what we provide here.
These tools comprise mostly of a half-inch thick piece of flat-bar stock with various holes in it and a piece of carefully selected tubing whose inside and outside diameters are carefully chosen. The flat-bar stock is some several inches wide and more than a foot long. The remainder of the related tools are mostly M8 coupling nuts, bolts, a few nuts and so forth and two larger sized bolts that are used to draw in a standard industrial "bearing splitter." ... The how, what, and why of this is explained below.
AT RIGHT: Here, the same tool is being used to pull the S1 side cover off of the bearing stuck on the differential carrier after the whole assembly being pushed out from the opposite side. Here, unlike above, the tube that the plate presses through the side bearings is in full view.
The inside, outside and length of the bit of tubing are easily determined. The outside diameter should be as large as possible and still easily fit through the side bearing. The inside diameter should be as small as possible but has to be large enough to fit over the axle ends. The length is more subject to choice but around two inches, or 50mm is around an ideal length. We helpfully chose tubing with a thick enough wall that we were able to cut a shoulder onto one end so that it goes inside the differential carrier as well as fully seating on the edge of the carrier. With a few mm worth of step like this, the tool stays centered and we are able to operate the tool with only two across-the-center draw bolts instead of the originally designed four since it doesn't tend to cock sideways thanks to the shoulder.
Similarly, the holes that need to be made in the flat bar are also easily determined by the actual parts - rather than trying to specify them here, anyone who wants to follow this path can simply look at the images here, measure the parts and do what's needed. ... In short, a hole that just fits over the an axle end is needed in the dead center, and then pairs of holes directly across from center are needed at the right distances from center for the alxe mounting flange studs and side-cover mounting studs. The coupling nuts thread onto these studs to let pulling happen with bolts from the outside - extra nuts can help with this. And, an extra pair is needed for a bearing-splitter to help get a stuck bearing off of the differential, as pictured.
BELOW: Below we see the same assembly in the image immediately above right where the bearing was stuck on the S1 side of the differential carrier. Here again, our special tool saves the day as can be seen here, using a standard "bearing splitter to pull the bearing off the carrier, much in the same way as if it was a side cover. Note also, the use of the factory differential holder that lets the assembly be held in a standard bench vise and also facilitates torquing the ring gear bolts.
Our standard procedures on transaxles includes:
Our experience with transaxles goes back to the late 1970s when one of us (Richard) built up a 2200cc engine and wanted the gears to match. In the late 1980s, getting someone to - or finding someone who would - rebuild a split case transaxle was nearly impossible. So, that's when we collected up the tools and began rebuilding them. We worked a deal with widely known and highly regarded Glen Wolfram of San Jose, California - the man who rebuilt transaxles for Harry Pellow. In that deal, about 1991, we secured a complete set of factory tools, a large pile of new and used parts, and Glen took Richard on as an apprentice wherein Glen imparted decades of wisdom and knowledge on transaxle rebuilding, especially including how to tell worn out parts from good ones by examination.