Of course, this could have been because, like so much else, it had seized solid during its long rest, so I thought it best to take it apart anyway.
It all comes apart logically, if a bit fiddly.
Do the front joint first, as it is easiest to handle. The rear joint is identical.
The Manual says you should mark the flanges to assist in refitting them in their original positions. I found that in fact the bolt-holes on the flanges would only allow re-assembly in one position, but it turns out you have to reassemble not only the flanges, but also the spiders and yokes in their original positions, with the grease nipple on the spider facing away from the flange, so you should mark everything. Try marking the flange yoke and the sliding sleeve yoke each on the side closest to the grease nipple on the spider: this gives a clear unambiguous guide to assembly. You also have to reassemble the sliding joint into its original position, so that when complete the front and rear joints are in alignment. The Manual says there are arrows marked on the splined sleeve and the splined shaft for this purpose. I couldn't find these arrows, so I also centre-punched the sliding joint so that I could reassemble it onto the same splines.
Unscrew the grease cover from the back of the sliding shaft, and slide the joint off the splined shaft. The bearings and races have to come out outwards, which isn't easy because you can't drive them out (the book says you can use a thin rod to drive the bearing out from behind, but I found this very difficult in practice). Take off the circlips, then ease out the bearing races by first tapping the yoke with a light hammer on the opposite side, and then prising it out with fingers - like getting cigarettes out of American cigarette packages. When the bearing comes out, do try not to lose the needle rollers: there are 22 of them in each bearing, they are very small and they take a long time to find, even on new clean garage floors. All four bearings come out the same way. The gasket retainer with grease gasket will remain on the spider: take this off too. The gasket is made of cork pressed into an aluminium retainer. I found that although the retainer had withstood the ravages, the cork itself had crumbled in every single case. With the help of an O-ring wholesaler, we found an O-ring of exactly the right size to fit the retainer: he wasn't impressed when after rifling through his entire stock, I finally bought just eight rings. Because he scorned to invoice me, I can't tell you what size they were: but they worked beautifully.
Reassembly is equally straightforward. You have to assemble the spider with the grease nipple facing away from the flange. In practice this isn't a major problem because if you do it wrongly, as I did first time, you'll find the universal joint has very limited universality, and you'll have to take it apart and do it right. You should be getting good at this by now. It helps the reassembly to smear the inside of the bearing with grease to hold the little .....rollers in place. If you drive the bearing too far in, the inside of the bearing race will bear on the thrust face of the spider, and the joint won't move freely. Just tap the whole assembly lightly, and it should free up. Don't forget the circlips.
Finally, the book says you must make sure the front and rear trunnions are in line; in practice this means reassembling the sliding joint onto the same splines; which is why you have to make sure they're marked before you take it apart. If you've got it all right, the grease nipples in the front joint and the rear joint should also be parallel, because that's how they were assembled originally.
There are several reasons for this:
- firstly, there are fewer Nuffield cars still on the road;
- secondly, everyone else can machine their axles to much better tolerance;
- and thirdly, it is racially prejudicial and therefore illegal to complain about whining Poms.
Unfortunately none of these reasons helps MG owners.
The whine comes from badly-meshed crownwheel and pinion hypoid gears. They come as a matched pair and must be replaced as a pair. For them to mesh correctly, the pinion must be exactly aligned longitudinally, and the crownwheel must be exactly aligned laterally. There is a complex series of spacers to get the alignment right (even the thickness of the gasket is counted - it has to be 5thou assembled, so make sure you use the right material). All the parts are marked - axle casings, crownwheel, pinion, and the spacers themselves - so that if you do have to replace anything you can get it all in correct alignment. But unless you know exactly what you're doing (and if you're reading this for guidance you don't!) my advice would be to take serious counsel before you do anything except dismantle and reassemble, and even then to take extreme care to get everything in exactly the same position. I once heard a story attributed to Colin Chapman, long before Lotuses were famous, when he was building and racing specials at University. He is said to have wanted to mix a crownwheel from one car with a pinion from another, and he's supposed to have made it work by filling the axle with Bluebell, and driving around until the noise went away. There is no evidence to support this implausible story: on the other hand, there is plenty of evidence to show that if you don't assemble this axle properly, you'll have to live with the noise for ever - or at least until it drives you mad enough to do it again.
Fortunately the axle is extremely rugged, and I've never had any trouble with the crownwheel and pinion.
I did once go through a phase of breaking halfshafts. I must have bought the entire stock of secondhand shafts in NSW, and when the word got out people started bodgying up the most dreadful offerings. I bought one shaft which had been repaired by drilling and dowelling the shaft then welding, grinding and smearing the joint with grease. It lasted almost 100 yards. The halfshafts always break adjacent to the spined joint where it fits into the differential gear; if you're lucky you can get the broken bit out by taking both half shafts out and poking the broken bit out, from the good side, with a straight bit of wire. If you're unlucky, you're up for a complete strip of the axle - and you really ought to do that as soon as possible anyway because when the halfshaft breaks the two ends grind together and shed nasty abrasive steel particles. Anyway, this phase came to an end, without my finding out why it happened, although I always carried a spare halfshaft after that (luckily both halfshafts have right-hand-threads, so I only had to carry one).
Another time I stripped a tooth on one of the differential pinions. To my complete surprise, I was able to drive the car normally afterwards, as though nothing had happened. I suppose that as long as the broken tooth wasn't engaged, the differential would work normally and moreover if both wheels revolved at the same speed there would never have been a problem thereafter (or indeed any need for differentials in the first place); but - perhaps because we drive on the left and therefore there are more left-hand corners than right (think about that!) - the differential rotated until from time to time the broken tooth came into alignment. What happened then was that the differential spun round until the next tooth engaged with a sickening clunk which shook the whole car, and all was well again until the next time. Eventually the next tooth failed, and the sickening clunk was a bit louder and the shake a bit more alarming. But the car still went apparently normally, until the differential was again aligned for the broken teeth. This happened a bit sooner, because the gap was bigger, but still quite manageable. The next tooth didn't last as long, and subsequent teeth less still. Eventually the missing teeth and the clunk came up about every hundred metres, and I decided enough was enough. Even then I drove about 6.5km home. When I stripped the axle, it was down to the last tooth - if that had broken, I would have been immobilised. But I'd been able to put the job off for quite a long time since the first tooth.
This axle is a pain to dismantle, compared with TCs, where you can take the differential out forwards.
On TDs, you have to remove the whole axle and separate the right half from the left to get to the diff.
First disconnect the propshaft. If you're going to have to take out the pinion, you should undo the flange/pinion nut (#26 in the diagram above) now. In fact you should do it anyway. The nut is tightened to 140 ft.lb: that is a lot of torque, in fact it is at the very upper limit on my torque spanner. You will need to find some way of preventing the flange from turning while you apply this much torque to it. I used a couple of feet of 2" angle iron, drilled to fit two of the flange bolts, and braced it against the ground while I undid the flange nut. Extract the flange and inspect its sealing surface. Mine was badly worn by the rubber oil seal (#24) which had hardened during the long layoff, and after rifling through my supplier's entire stock of used parts, I couldn't find one which was not worn, which leads me to think it is likely to be a universal problem. (Because I thought I could get away with this, I didn't do it straight away, which meant I had to do it later. The worn flange meant the oil seal was defective, and that meant the expensive axle oil was sprayed in a vertical circle all over the back end of the car. But the really serious problem was that the wheel bearings are lubricated from the axle oil, and when it had finished lubricating the road, there was none left for the wheel bearings. We were lucky that only one failed, and that it failed before the axle and differential. So I cleaned out the debris from the failed bearing, sleeved the flange with a Speedisleeve, renewed the oil seal, and there has been no more problem. But what should have been a simple job if I'd done it at the right time turned out to be a royal pain.)
At about this time you should take off the rebound rubbers and check strap. If the body is off, you may have to compress the springs to be able to remove them - about 50 housebricks does it (see the picture below). Then prop up the chassis, and gradually unload the springs.
Now take off the brakedrum and hubs, then the brakeplate assembly. This lets you take out the halfshaft, complete with bearing, housing and oil seal. Now you have to remove the two U-bolts on each side holding the axle through the locating pads; this also releases the brackets holding the shock absorbers. Then undo any other bits I've forgotten about, and you can now remove the whole axle sideways (while its out, take the opportunity to inspect and recondition the springs and suspension).
Now you can undo the ten nuts holding the axle cover to the axle case (ie bolting the left half of the axle to the right half). The studs should remain in the case. Separate the cover carefully, and now you can lift the crownwheel and differential out of the axle case (the right hand half). The bearings are a press fit on the diff case, so they should stay on the diff assembly, and the spacers normally stay in place in the recesses machined for them in the case and cover respectively. Leave them there, or if you must take them out, mark them carefully so they go back in exactly the same position. It's unlikely that you'll need to do more than inspect and verify the bearings; but if they do need replacing, do make sure you get bearings of the same width: they're part of the alignment, and if you can't get identical bearings, you'll need to get different spacers, so that the combined width of bearing plus spacer is constant. I have no idea where you'ld get new spacers. The pinion remains in the axle case, and it takes special tools to realign it after removal; leave it there unless there is good reason, eg evidence of damage to the pinion or worn bearings or leaking oil seal .
If you need to, you can now dismantle the differential gears by bending up the lockwasher on the bolt holding the pinion pin (the shaft which the differential pinions run on) and removing the pin. You can take out the pinions together with their thrust washers, and then the differential gears with their thrust washers. I always like to keep the parts together - each pinion with its thrust washer - but that's probably paranoia. Leave the differential case bolted onto the crownwheel, again unless there's good reason to dismantle it.
Reassembly is quite straightforward, unless you've had to replace anything at all except differential gears or pinions, in which case you're up for some serious arithmetic which quite frankly is beyond my ability to understand far less explain. The real trouble is, you can't tell it's wrong until you drive the car, when the whine will drive you - to distraction.
First reassemble the differential - and this is the only fiddly bit. Place the differential gears in position with their thrust washers. Then engage the pinions with their thrust washers through the holes in the cage, and rotate the gear/pinion assembly inside differential cage until the pinions are aligned with the holes for the pinion shaft. Drive in the pinion shaft until the locking bolt can engage, then do up the locking bolt and turn over the tab washer. Easy.
If you had to take the crown-wheel off the differential case, put it back on: no tricks here, just tighten the eight bolts and turn over the tab washer. If you took off the bearings, press them on now. Make sure they're pressed fully on, right up to the shoulder on the diff cage. Make sure the spacers are in position in their recesses in the case and cover: if you removed them, make sure you put the right one back, or if you replaced the bearings, make sure your arithmetic is correct, otherwise the crown-wheel won't align properly with the pinion (as discussed above). The diff assembly goes back exactly as it came out, meshing straightforwardly with the pinion, and the cover bolts straightforwardly onto the case. There are no washers for the nuts. The alignment system assumes a 5 thou gasket (compressed), so you must get a genuine MG part, or make sure you use suitable material for the gasket; if you want to leave the gasket out and use silastic instead, you have to allow for the difference in choosing the spacer on the cover side of the axle. Easier to use the proper gasket.
Replace the axle, and tighten the U-Bolts through the locating plates and damper bracket, always using new rubber pads because they're so cheap. Don't forget the locknuts. You'll probably need to compress the springs in order to be able to bolt up the rebound rubers - about 50 housebricks does it for me every time.
Lord Nuffield managed to find one more opportunity to confuse poor amateurs like us. Not content with the variety of threads already existing elsewhere on the car (BA, BSF, Whitworth, metric, brass threads - 26tpi - on the windscreen), the British Standard Fine (BSF) threads on early axles were replaced with American National Fine (ANF) threads, and later still with Unified threads. You can tell Unified threads by the markings on the nuts and bolts - although the method of marking itself varies. If you have ANF threads, only the wheelnuts are marked, and to add to the confusion they use the same marking as Unified wheelnuts. And of course if you have BSF nothing is marked. Good one, eh? Luckily ANF and Unified threads are pretty close to each other, and nuts and bolts fit each other; but neither will fit BSF. If you're seriously into concourse restoration, you'll want to make sure that your car has the correct thread for the period. And I'm sure you'll want to bring this to the judges' notice, and they'll give due credit for your pedantry.
Don't forget you'll have to bleed the entire brake system.