For the past couple of years I’ve been trying to track down a decent 3.9-1 ratio gearbox (currently have a 4.1-1 box with doggy first gear). I had a spare which came with the car but that has corroded internals. Then a couple years ago one popped up on eBay. Had been in storage for years so condition unknown. It was cheap but of course a risky purchase. On opening up I found again there was some corrosion. Then this summer another one appeared on eBay, again I seemed to be the only one interested and again condition unknown. After explaining my previous experiences the vendor kindly agreed to remove the bell house to check. No sign of corrosion so a deal was done. Once home I stripped down to check bearings and condition of gears especially first gear as believe they have a tendency to wear out their syncros. Those were fine but what wasn’t was the lay shaft keyway in way of the end gear. See photo (top one). No problem I thought, have some spares. Interestingly the first one I looked at had the same issue albeit not as far gone, a hair line crack (middle one). Luckily the second was fine. I concluded that the shaped end of the key (which was the same on all three shafts) wasn’t helping and replaced that with a full key. Reassembled and in the car working well so far. Recommend checking this keyway when doing a gearbox rebuild. Finally, if anyone needs an odd bit for a gearbox rebuild I may be able to help. Hope this article is of some help/interest.
