Test drive
Drive the vehicle far enough to see the temperature gauge needle rise and settle to normal. When you’re confident of the safety of the vehicle, take it up to around 60mph, noting any vibration as road speed and engine speed increase. Drivetrain vibration feeding through to the cab may be due to out of balance propshafts and/or partly seized universal joints. A sudden rear end noise on overrun can be caused by a seized sliding joint in the rear propshaft.
CHECKING THE RIDE AND FEEL
Steering vibration is usually due to tyre/ wheel imbalance, but also worn or poorly adjusted swivel bearings, especially if the steering feels a tad wobbly over potholes. Underside knocks and bangs suggest worn suspension bushes, though even good bushes can be audible over poor road repairs and potholes. The Panhard rod bushes, if worn, will allow the steering to wander.
Directional changes when braking may be caused by partly seized or inefficient front brakes. Locking up of a rear wheel under heavy braking points to poor rear drum brake adjustment or a single inefficient brake, possibly oil leaking onto the brake shoes. The latter is common if the axle seals are worn and the vehicle is parked on a side slope, allowing axle oil to flow out into the brake drum.
A slight directional change (corrected at the steering wheel) can occur during gear changes when accelerating hard, and also when suddenly backing off the throttle. This is typically caused by movement in the rear radius arm bushes allowing the rear axle to move slightly out of line as engine torque is applied and released.
Excessive lean in corners, especially coupled with front dive when braking, suggests the dampers need renewal. There’s little to go wrong with coil springs, though they can become slightly compressed with age.
Listen for worn front wheel bearings when gently cornering; rears will be heard rumbling when driving straight on a light throttle. Also listen for the tick sound of failing CV joints in the front axle when turning slowly on full lock. Transmission bearings can whine, but the sound isn’t usually transmitted through the chassis/ body so can usually be pinpointed to the gearbox, transfer box or differentials.
TESTING THE DRIVETRAIN
It’s always worth seeing how the truck
copes with a long steep climb (if there is one locally). Check for exhaust smoke under load which can suggest general bore/ piston ring wear, and confirm the coolant temperature stays down. If a diesel begins to run out of puff, it may just need a new fuel filter cartridge.
Grey smoke from a diesel engine, especially coupled with a reluctance to stop when switched off, suggests a failed head gasket is allowing lubricating oil into a cylinder where it is burnt, thus keeping the engine running. Blue smoke suggests serious bore/ring wear and any other smoke is usually due to incorrect injection pump timing, though also pump and injector wear. Beware a rattling injector pump – rebuild needed.
TRANSMISSION
The more common five-speed manual gearbox has synchromesh on every gear, so expect it to change freely and quietly, and to stay in the selected gear, especially on the overrun when decelerating. If the gearbox is noisy when in neutral with the engine idling, notice if the noise disappears when the clutch pedal is pressed, which suggests the layshaft bearings are worn and a rebuild is due.
Always check that low ratio and diff-lock work okay and are easy to select (the vehicle may need to roll a little to fully engage). The diff-lock warning light will show on the instrument panel when engaged, and you’ll feel the steering pull a little when testing a short distance on tarmac. When deselecting diff-lock, the light might stay on initially, and sometimes it’s necessary to reverse a little to remove any axle wind-up.
Note that early V8 models had a four-speed synchromesh transmission known as the LT95 which combined the gearbox and 2-speed transfer box in a single unit (also used on the early two-door Range Rovers). 1983 and very early 1984 vehicles had selectable four-wheel drive (similar to Series III). So, no diff-lock fitted, but check it all works. It’s very rare.
Expect a fair amount of slack in the drivetrain, which is normal; for example, after applying the transmission/hand brake with the gearbox in neutral, the vehicle may roll a little when the footbrake is released.
AFTER THE DRIVE
After the test drive, and with the engine switched off, check the engine bay for oil and coolant leaks, and for oil film deposit over the top of the engine suggesting cylinder wear and/or head gasket failure. Look for leakage from the coolant pump shaft and manually test it for looseness.
When the engine has fully cooled and the coolant system depressurised, check the coolant level. Also remove the oil filler cap – white fluid on the underside suggests a mixture of oil and water which could be due to a head gasket leak or just condensation in the engine, depending on its condition.