I have been asked by some newbies lately about the rear axle seal kit, the components, and why some leak. So here is my take on the topic.
A seal kit will have a large O ring, a small O ring, a seal, two paper gaskets and a thin washer. Only one paper gasket is used, the other was intended to be used on an early bus reduction box.
When VW was still air cooled, the thin shim was a hardened item. Today it is a soft piece of metal- unless you get the Sabo seal kit. Their shim is still hardened- not to the extent of the original VW but it comes close.
And that is where the question arises. Do you use the shim? ( I do)
The purpose of the shim was to go against the axle bearing so that the small O ring would not get chewed up by the spacer for the brake drum. The soft metal shim found in most kits - even the German one will actually distort when installed and thereby allow the small O ring to be pinched between the spacer and the bearing. For that reason, some actually will leave out the thin ( soft) shim.
So why the shim to begin with. The original VW drums were made of a very different material than what is currently available. You can tell by the "ring" if you hit one with a hammer. The shim acted as a spacer on the axle and with a tapered axle with splines, the drum could only go on so far. With the current "softer" drums, one can actually over tighten the drum ( without the shim) and expand the splines inside the drum. Loose drum after one weekend sound familiar? And while on that subject, a cotter pin in the hole does not mean the drum is tight. If the splines are worn, the pin will still be in the hole but the wheel will be loose. Good to check often.
So what causes a leak? Small O ring chewed up, loose drum, bent axle, incorrect assembly of the gasket and the large O ring, and in the rare case, a warped bearing retainer (not often). Lastly, the spacer with the bevel can get rough inside the bevel and eat up the small O ring. Always good to check that also.
Hope this helps.
Dietmar
www.quixoteracing.com