MORE TRANSFER BOX TROUBLES
While I was waiting for a new LT77 gearbox to arrive I turned my attention to the next job, which was another vehicle that had come in for a 200Tdi conversion and ended up with the transmission sitting on the floor. It was however a different vehicle with a rather different transmission, being a 1973 Series III with the four speed gearbox with part-time four-wheel drive. The owner had mentioned that the gearbox seemed a little noisy, and asked me to check it out.
In the lower gears, drive is transmitted via the layshaft: in fourth gear the input shaft and mainshaft are locked together, with no load on the layshaft. So if a gearbox is noisy in every gear except fourth, it does not take Sherlock Holmes to deduce the likely source of the noise. Layshafts have always been a problem on Series gearboxes. The pre-1971 units (with no synchromesh on first or second) had separate gears splined onto the shaft that fractured at the sharp corners where the splines were machined into the shaft.
For the Series III the layshaft was made in one piece with integral gears, eliminating the fracturing problem. However, at the same time the nut and split pin securing the front of the layshaft to the bearing were replaced with a bolt. This was not provided with any mechanical means of retaining it in position, relying on Loctite on the threads, which must have been in short supply in 1970s Britain, judging by the number of SIII transmissions I have seen with the layshaft bolt loose. A loose bolt allows the layshaft to float backwards and forwards relative to the mainshaft, which is not so good for the gear alignment (hence the noise) and eventually chews up the rear layshaft bearing and the gearbox casing.
I split the transmission into its two parts and started to strip the gearbox. I was already sure of what I would find, and sure enough, when I removed the front cover the layshaft bolt and washer fell out onto the floor. I could have got away with just fitting a new bolt (using plenty of Loctite) but these gearboxes come apart very easily without special tools, so I carried on until I had a bare casing and a pile of gears and shafts. The casing had not been damaged by the wandering layshaft and all the other components were in good condition, so I put it back together with new bearings and seals.
I then stood the gearbox upright, bellhousing downwards, on my custommade gearbox dismantling stand, lowered the transfer box onto its studs, did up all the connecting bolts and slid the intermediate gear cluster into position. It was at that point that I noticed that the output gear had a broken tooth...
That sort of damage is normally caused by something solid getting jammed between two gears at high speed, and I have to say I have never seen a broken gear tooth on a Series transfer box before. I carefully inspected the intermediate gear and none of the teeth had the slightest mark on them. The gear tooth was broken across three quarters of its width, leaving just enough to be able to transmit drive without a clicking noise to give itself away, which was why I hadn’t picked it up on the road test.
The gear would need to be changed, and fortunately I had a good secondhand gear in my stash of Series gearbox bits. The bad news was that some idiot had managed to break the ears off the circlip holding the broken gear to the output shaft, leaving me with no obvious means of removing the circlip. Luckily the circlip had worn so badly I was able to slide a thin hook tool under one of the broken ends and prise it out from its slot. Even better, I found a circlip of the correct size in a box of sundry parts. So the transmission is now back together, hopefully free of leaks for now and fit for further use.