Gearbox Teardown

The gearbox is now in several pieces on the garage floor. The rear brake calipers are all cleaned up (only three cans of brake cleaner and half a roll of paper towels) and waiting to be installed on the new transmission. The sideplates came off the gearbox without too much trouble, exposing the differential and the ring & pinion gears. The gears and the diff carrier – originally different shades of silver and grey – are now all an even brownish blue tint, indicating severe overheating and a patina of burned gear lube. All of the teeth show signs of galling. Strike that assembly from the list of potentially salvageable parts.

To take the gearbox apart further will require removal of large castle nuts from the pinion shaft and the layshaft. This is normally very simple: Put the transmission in two gears at the same time, and the two shafts will not turn when you put a wrench on the nut. Unfortunately, the transmission cannot select any gears at the moment. The layshaft nut came off by hand, which was a pleasant surprise, but not pleasant enough to outweigh the discovery that the layshaft was broken from flailing around when the rear support bearing fell apart. Scratch the layshaft from the list.

Since the pinion shaft can’t be locked to the layshaft, there is no convenient way to hold it from turning while the castle nut is loosened. A big pipe wrench on the pinion gear could work. Damage to the pinion gear is not a concern, since the pinion gear was already off the list. The trouble is that the wrench may dig into the main case and take it off the list as well. On the other hand, removing the pinion shaft is the only way to keep the case on the list. Will the cure kill the patient?

Removing the input shaft will require a bit of ingenuity. The input shaft is stuck in the case, retained by the splined coupler which holds it to the layshaft. The coupler is stuck to the input shaft until the broken end of the layshaft drawbolt comes out of the input shaft. That can’t happen until I can get at that end of the input shaft with a drill, which won’t fit into the case – which the input shaft is stuck in. I may have to cut apart the coupler, which would scratch it from the list. Otherwise, scratch the (new) input shaft, too. I have an idea, though. I’ll let you know tomorrow if it works.

The ever-shrinking list of potentially salvageable parts now includes

• the main case
• the side covers
• the stub axles
• the bearing carrier
• the rear cover
• the gearshift selector finger
• and the input shaft.

That looks like a lot until you consider that the gearbox is made up of some 150 parts, not counting all of the shims and spacers that make everything line up properly.