4 Speed Transmission Repair Tip
Subimtted by Skip: (pococj)
Here's my fix for the HD ratchet top or hand shift top 4 speed tranny. I don’t know if it applies to the cow pie top of the later years, so check your manual to see if these parts are interchangeable. As long as I kept the sprocket nut tightened there were no leaks.
First, your main drive gear and bearings must be in good shape. Get a new cork gasket, a new keyed main drive gear spacer (some of 'em came without a key slot and key, as mine did originally), a double lip main drive gear oil seal, a new sprocket, and a new sprocket nut with a seal on the inner surface and an O-ring type of seal on the backside. Check the surface where your new double lip seal will mate with the tranny case. If it has any burrs, scratches, etc., you'll never get a seal for any length of time. Clean the burrs, etc. with a piece of sandpaper on a small diameter wooden dowel. Do not work in one area so long you make the cavity out of round., but work it just enough to remove the burr or deep scratch.
Start the assembly process by installing the cork seal, and then almost filling the remainder of the cavity with a non-hardening gasket compound (I've also used hi temp grease), leaving just enough room for the spacer and double lip seal to fit in the cavity properly.
Next coat the outside of the double lip seal with the non-hardening gasket compound and install the seal to the depth specified in your manual. Make sure it goes in straight and evenly. The gasket goop on the outside edge should seal any small scratches and gouges on the mating surface.
Put a little tranny lube on the lips of the seal and install the keyed spacer over the shaft and into the tranny cavity. (If your bike came with the unkeyed spacer, see the note below.) Don’t damage the seal lips. Now install the new sprocket, and the new “supernut” with the o-ring seal to the sprocket. Put some blue Loc-Tite on the threads and tighten the nut to the spec listed in your manual. Install a new chain, and reassemble the inner primary, starter motor, clutch assembly, and outer primary.
As long as I put everything together this way my 78 FLH never leaked. Keeping the sprocket tight is mandatory. Can't count the number of times I tore into a BT tranny and found the sprocket nut loose; it was an almost always thing.
NOTE: Some bikes came with a main drive gear spacer that wasn’t keyed to the shaft. Sometimes the spacer would turn on the shaft and cause wear on the two mating surfaces. If enough wear occurred, no sealing is possible, because the oil will run between the shaft OD and space ID. If you have a non-keyed spacer, replace it with a new keyed version, and closely inspect the OD of the shaft. If any wear is present, and the shaft is in good condition otherwise, try smearing some of the non-hardening gasket compound on the ID of the spacer before installation. Or you could machine an o-ring groove in the ID of the spacer, install a thin o-ring, and then installing the spacer. There’s not much “meat” in the spacer, so this last method might not be satisfactory.