[Big D]

Hi all,

The gearbox assembly was an interesting exercise. You will recall I had to replace all the synchro rings and third gear so I had to completely dissemble the mainshaft. The mainshaft is reassembled on the spline in this order: Second gear, thrust washer, 2nd gear synchro ring, synchro hub assembly, 1st gear synchro ring, 1st gear, reverse gear.

I had a retired mechanical engineer give me some assistance which was great as he had rebuilt countless gearboxes in his career and at times during this rebuild I found two heads were better than one with a couple of little hurdles that I struck.

The main problem I had was that the new 1st and 2nd gear synchro hub assembly was a very tight fit on the mainshaft spline. The manual refers to ‘sliding the synchro hub assembly’ onto the splined shaft during reassembly. These hubs were never going to slide on. The old hub had to be pressed off and the new one had to be pressed on and we tried various methods in doing that, with the first gear down on the press and then first gear upwards on the press.

The difficulty with pressing the assembly on was that you had little control over the thrust washer and 2nd gear synchro ring positions once the process of pressing the assembly on started. The slightest movement of the first gear or the shaft would change the position of the thrust washer and then the teeth on the synchro hub assembly would not align properly with the thrust washer meaning the hub had to be pressed off again. The other problem was that if you pressed the hub assembly on with first gear down (shaft into hub), you couldn’t control the position of the synchro ring and this had a tendency to cant on the shoulder of second gear, at the last stage, meaning the hub would not go on any further. One also needs to be careful to keep the synchro hub together as an assembly during that pressing to ensure the locking rings inside the hub didn’t come away from their position in the process.

We repeated this process about 5 times trying different things to get the synchro hub aligned into the correct place. Finally, we decided to put a smidgeon of Loctite on the top surface of the thrustwasher to hold it at its precise location on the shaft splines long enough to get the teeth in the top of the hub assembly to align with it. As soon as torque was applied the Loctite broke away but it was enough to do the trick. We pressed the hub on with second gear down (hub onto shaft) and also used a little tool to hold the synchro ring up tight against the hub assembly as the hub was pressed down.

I’m not sure if all the synchro hubs are this tight, or whether it was this particular shaft and hub(s), but if the hub was a sliding fit as per the manual, then I wouldn’t have had these issues.

The rest of the gearbox assembly was relatively straightforward. I replaced all the bearings in the housing, most obtained off EBay at very reasonable prices. One of those bearings appeared to be just slightly different in thickness to the original meaning the end circlip was too tight a fit in the groove on the shaft. In the end, I cleaned up the circlip on a very fine bit of wet and dry paper and it worked fine. There would have only been maybe 0.001” in it, but it was enough.

I fitted the bell housing and set up all the clutch release bearing assembly. I need to find a spring now for the clutch release bearing sleeve. The gearbox is now painted and just about ready to fit.

The brushes for the starter motor arrived. These weren’t originals but they do fit and they should work fine.

That is all for this week.