Q. When I bought my 1999 Freelander XDi just over a year ago, I noticed some vibration from underneath between 40 and 50mph, and another noise that was present only when I slowed down.
I replaced the rear diff hangers and the viscous coupling unit (VCU) bearings, and this has eliminated the noises. But there’s still slight vibration from 50 to 60mph. The front propshaft looks to be newer than the back. Could this be a balance problem?
A. It sounds like a balance problem in the driveline, but do a few checks before concentrating on that.
Confirm the tyre pressures are correct, that there’s no unusual wear and that the wheels are correctly balanced.
If you’ve replaced any tyres, those with the largest diameter should be on the rear. Check each tyre’s working radius by measuring from the axle centre to the ground on each wheel with the vehicle standing on level, firm ground with correct tyre pressures and with no heavy items on board.
There may be an imbalance in one of the propshafts. You could visually inspect them to see if a welded balance plate has corroded and come off. Otherwise there may be some wear or sticking in one of the propshaft universal joints, at the rear end of the front prop and at each end of the rear one.
If you think the front shaft has been renewed, check the rear first. Disconnect it from the diff and move the joint flange through its full articulation while feeling for looseness and restriction in the movement. You can check the front joint in this rear shaft while it’s disconnected from the diff, though you’ll need to swing the prop through an arc to test the movement.
Assuming the balance weights and joints are okay, you may need to remove the prop assembly – including both shafts with the VCU attached – to have it balanced by a transmission specialist who has the necessary equipment.
There are other potential causes of vibration, such as worn driveshaft bearings, bent driveshafts (if you’ve been off-roading enthusiastically), steering joints or hub bearings.
A worn CV joint may be detected as vibration, though in early stages of wear they usually show as a knocking on tight steering lock at low speed.
Wear in the rear diff or in the intermediate reduction drive (IRD) output bearings and gears can cause vibration, but these rarely cause problems unless aggravated by a partly seized VCU. And if the VCU were seizing, you’d have noticed poor handling and steering response.
After doing these checks, move on to the propshaft assembly.