You turn the key and get a loud... NOTHING.
I have owned rear-engine Porsches and VWs since 1974. I can't remember a single one that I've owned that did not have an occasional no-crank issue at some point in its life, either when cold or hot. Replacing the starter with a rebuilt Bosch unit would remedy the problem for a while, but sure enough—within a year or two—the same exact problem would return. For years I mulled this over, scheming possible solutions. This is the type of thing that drives engineers crazy.
One common theory was that the ignition switch was located too far from the starter, and the resulting voltage drop (because of the long wire), coupled with the high current demand of the starter solenoid, was so great that there simply was not enough power at the starter to make it go. On that premise, many people (myself included) tried to remedy the problem by adding a load-reduction relay or Ford-type starter solenoid back near the starter. In fact, the Bosch corporation actually made such a kit (their "WR-1") specifically for rear-engine VWs and Porsches. With this set-up, the ignition switch and (long!) length of wire would have to supply only enough power (very little) to trip the relay. Great idea! The only problem was... it didn't work consistently. I continued to puzzle over it for another ten years or so, until I finally got so frustrated that I really started studying the problem. I discovered that the issue was in the design of the starter itself.
The original Bosch starter design is actually two cylindrical parts bolted together: a solenoid and an electric motor. The assembly of the two is the "starter." The smaller of the two cylinders is the solenoid, and the larger is the electric motor. The solenoid is an electromagnetic device. Inside this small cylinder is a smaller (and also cylindrical) solid iron core with a couple of miles (literally!) of copper wire.
The wire is wound around in such a way that it surrounds the iron core, but does not touch it. When current flows through the wire, a magnetic field is created which causes the iron core to get sucked up inside the windings, thereby creating a pulling force. One end of the iron core is mechanically linked to a seesaw device that operates a "Bendix" drive, which has a small gear on it. That small gear mates with the big gear on the flywheel, which is bolted to the crankshaft of the engine. By pulling on one end of the seesaw, the iron core within the solenoid engages the two gears together. At the other end of the iron core is a big, fat switch. It is through this switch that the electric motor gets power via the big fat wire that is bolted to the starter and goes straight to the battery. So now, with the two gears mated, and power supplied to the electric motor, the engine cranks over. Seems pretty simple and bullet proof, right?
I started studying the starter circuit and noticed that the solenoid actually has two separate sets of electrical windings. One set is called the "pull" set, and the other is the "hold" set. The pull set is much stronger than the hold set, which is made possible by more loops of wire. What is interesting is that the pull set gets its ground path through the windings of the electric motor. The hold windings get a separate ground path directly to the chassis ground. So, when you turn the key in the ignition switch, electricity has to flow through the mile of wire between the ignition switch to the solenoid, then through another few miles of wire that are the pull windings of the solenoid, and then through another million miles of wire that are the electric motor windings. When everything works right, the solenoid pull windings yank on the iron core, which engages the Bendix drive. The other end of the iron core energizes the motor windings. That gets the motor spinning, but in doing so kills the ground path of the pull windings, so the hold windings keep everything going until the ignition key is released. The problem with this design is all the light-years' worth of wiring.
My theory is that the resistance of all that wire increases with age. Thus, when these vehicles were new, the system would work fine for years and years. The reason replacing the starter with a rebuilt one does not solve the problem is because these rebuilt starters have old wiring in them. When Bosch rebuilds the starter, the motor section just gets new brushes, bushings, and maybe an occasional armature and solenoid. And since these vehicles have been out of productions for so long, brand new Bosch starters of this design are no longer available.
The solution is to replace the starter with a brand new one of a completely different gear reduction design, often referred to as “high torque." The gear reduction concept itself is not new—Chrysler products have been using the design since the '50s. If you're a true gearhead, you probably always wondered why a 1966 Dodge Dart has such a wheezy sound when it was cranked over to start. Well, it's the gear reduction starter. By using a gear reduction principle, a smaller but faster spinning (4.44:1 in this case) electric motor can produce more torque with less current (the GoWesty starter produces between 40-75% more torque than the original Bosch starter). Why all starters were not made like this from the beginning is anybody’s guess—it was probably cost-related, but who knows? Another advantage to these new gear reduction starters as it applies specifically to this application is that they are a "self-supported" design. The original Bosch starter fitted to manual transmissions relied on a bushing in the bell housing of the transmission to support the loads between the drive gear of the starter and the ring gear on the flywheel. Bosch conveniently proivded a new bushing with the starter, but replacing it was anything but convenient—so it would be routinely skipped by the installer, which led to a whole new set of issues.
So GoWesty started offering brand new gear reduction starters for Bus and Vanagon around 2002. And while they immediately solved the common no-crank problem of the rebuilt Bosch units, the quality control of these first gear reduction starters wasn't great. It was basically like jumping out of the pot and into the fire! After a couple of frustrating years, we reluctantly went back to Bosch starters. But that was like jumping out of the fire and back into a larger fire. Not only were Bosch rebuilt starters getting even older, but now Bosch was mixing up their (dwindling) core supplies. In addition to getting marginal quality starters, they were showing up outright wrong—but it was the only game in town, and we had to offer some type of starter for folks caught in the lurch. This whole experience really put a black eye on our starter program, and much has been (erroneously) written about the ordeal. However, we weren't about to give up, and we kept rattling the cage of the gear reduction starter camp.
Meanwhile, behind the scenes, we kept rattling the cage of the gear reduction starter camp. With continued pressure, we were able to secure some key design changes to their starters that eliminated the issues we were having. This new generation of gear reduction starters features higher torque and superb quality. One key improvement we made—which is an exclusive feature of the GoWesty starter—is a bolt-on trigger wire, which means no more fiddling around trying to keep that wire in place. Our starters come with a short harness that bolts onto the starter at one end and plugs into your factory harness at the other, inside the engine compartment where you can actually get to it, and keep it high and dry—out of the elements. This feature is particularly well-suited for the Syncro application, where getting to the starter connections is… well, let’s just say it is challenging!
Our new exclusive GoWesty gear reduction starters costs only slightly more than a rebuilt Bosch starter—but they are WAY more reliable.
You know what they say: If at first you don’t succeed… you keep trying until you can turn the darn key and fire up your van!