Sorting the propshaft

Tracing noises on modern motors is tricky, but a suspect propshaft is easily removed for testing and refit or replacement. Ed Evans explains how

Tracing noises on modern motors can be tricky but easily resolved

APART from tyre noise, it’s reasonable to expect a Discovery 3/4 or Range Rover Sport to run relatively silently. So when my Sport developed a high-speed whirr, a low-speed tick, and a faint rumble, I added the three together and guessed at a worn-out propshaft, which seems reasonable after 130,000 miles.

The propshaft on these motors has a centre support bearing and a constant velocity (CV) joint in the centre, with a Hooke-type universal joint (U/J) at the rear attaching it to the rear diff. The shaft is actually in two sections: the front section bolted to the transfer box flange and its rear end supported by that centre bearing. The rear section with its CV joint is splined into the front section, and it’s not intended for the two to be split.

A worn support bearing will transmit the usual rumble noise. Problems in the CV joint are likely to cause a tick or click similar to a worn front axle CV on full lock. And the rear U/J may give the usual knock when taking up and releasing drive. The centre bearing is held in a circular rubber mounting, bonded to the bearing and to the outer support bracket which is bolted onto the underbody. This insulates, and absorbs the radial load on the bearing so, when it splits away from the outer support bracket, it can allow the propshaft to whirl out of alignment. This can produce a buffeting sound, similar to the air pressure effect of driving with a rear window down at certain speeds. If the shaft is out of balance, due to loss of a balance weight or a joint problem, it can cause a general vibration through the body, changing with road speed. Of course, similar symptoms can be caused by other components in the driveline.

All parts are lubricated and ‘sealed for life’ – the life of the part, not the car, which, in reality, means there are no service requirements, nor is it practical to service them. So, when one part fails, the official (and I think best) option is to renew the complete shaft, though it is possible to renew just the centre bearing assembly (see separate panel). If removing the shaft for inspection and refitting, mark the flanges so they are refitted in the same orientation.