Propellor Shaft Maintenance

The standard  propeller shaft on the Z Magnette has a universal joint at each end and the front end also carries the splined slide joint that allows the effective length of the shaft to change as it accommodates the movements of the rear suspension. Each UJ has four joints with a needle roller bearing in each. The central cross-shaped component is known as the “spider” and the twin-holed pieces into which the spider and bearings fit are known as “yokes”.

Each of the universal joints has a grease nipple lubricator and the scheduled maintenance is for this to receive three or four strokes of the grease gun every 1,000 miles (1,600 kms). The grease is carried to the roller bearings through drillings in the spider and can generally be seen emerging from around the rollers when new grease is introduced. Failure to emerge is generally a sign of blockage. Because this task is not particularly easy to carry out it is one that is often neglected. However, the joints are subjected to constant motion when the car is moving, so such neglect is likely to lead to problems. The slide joint is lubricated from the gearbox oil, so requires no other attention.

It is a good idea to check the joints for wear whenever the opportunity presents itself when the car is raised for other reasons.  By gripping one side of the joint and attempting to twist the other, one can detect any circumferential movement. Looseness here indicates that the needle roller bearings need replacement. If the forward end of the shaft feels loose in the gearbox rear end, it suggests that the splines are worn.

Wear in the joints can often be revealed by noise, especially rhythmic knocks that increase in frequency with speed. Another indicator is a distinct click as drive is engaged and the car begins to move forward. This sort of noise can also originate from wear in the rear axle, so before you start dismantling the differential, check the UJs; they’re a lot less expensive to fix! Noises can sometimes occur slowly and progressively and the driver does not notice them over a period of time. It is only after replacing the joints that the wear-induced noise becomes noticeable by its absence.

Replacing the universal joints is a straight-forward task described in the workshop manual. It is easier if you have a bench that can take the length of the prop shaft, because it is unwieldy when working on the joints and is disruptive if not held steady. One key issue is to mark the position of the circular flanges on the shaft before they are dismantled. Use a dab of white paint or correcting fluid across the edge of both flanges while they are still bolted together and make sure you don’t inadvertently erase the marks while you are working. A more durable alternative would be a pair of light centre-punch marks. As the joints are likely to be gunged up with a combination of grease and road dirt, it will usually be necessary to clean them in situ, so that the marks can be applied. For the relatively small cost involved, it is also worth acquiring a new set of flange bolts and nuts before you start the work. You may find that the old ones are worn or damaged or, worse still, if they are very tight or badly rusted you may have no alternative to inflicting some damage to get them off. The nuts are the self-locking type and no washers are required. It is, in any case, best practice to fit new self-locking nuts rather than re-use them.

When you reassemble, match the marks to make sure the shaft is in the same original position relative to the other components or you may induce an imbalance that causes a vibration. The needle roller bearings can also be fiddly and need to be held in place using grease during reassembly. As with most bearings, you need to make sure that they are straight as you drive them in or they will go off-true and bind. It is easiest to install the bearings with the spider on the flange yokes first before fitting that assembly to the yoke on the shaft. If you are looking for a suitable circular drift to push the bearing in, your socket set will often provide the solution. When reassembling, make sure you get the position of the grease nipple right. It must not foul the yokes, whatever the position of the joint.

If you find that the joints are so neglected that the bearing housings in the yokes are damaged or ovalled, the shaft will need to have new ones fitted by a transmission specialist or you may be able to find a good shaft on the second-hand market. This is not as unlikely as it sounds because any owner that has fitted a different gearbox is likely to have a spare shaft.  Few later gearboxes used the same sliding joint arrangement. MGB gearboxes, for instance, have the sliding joint in the shaft itself, with the UJ flange on the back of the gearbox.

If you do encounter shaft vibration that cannot be eliminated by changing the position of the flanges relative to eachother, there is an old trick that is reputed to be effective, though I cannot personally testify to this. You put a jubilee clip round the shaft. The clip is heavier on the side where the worm screw housing sits, so by experimenting with the position of the clip and the housing, it is possible to use the differential weight distribution to rebalance the shaft.

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