Splines are the longitudinal teeth on a driveshaft where it enters the hub or the gearbox. The joint transmits all the torque and is supposed to have no clearance at all. When the teeth are crushed or worn, angular play appears between the shaft and its mating part: at every change of load the shaft first takes up that clearance and then strikes. Hence the characteristic sound, which is often mistaken for a suspension fault.
What it sounds like
The classic picture is a single dry click or dull knock at the moment the load on the driveshaft changes sign. The most telling regimes:
- Pulling away. A click from the wheel side in the first metre, then silence.
- Swapping throttle and brake. Lift off, get back on the throttle and the knock repeats exactly at the transition.
- Reverse after forward. The play is taken up the other way and the click is especially clear.
The key difference from the suspension: the sound is not linked to bumps. On smooth tarmac it is there; over a speed hump without a change of drive it is not. Another marker: as wear grows the click becomes a double one and starts coming with a slight jolt felt through the steering wheel.
What is checked and how
The diagnosis is done on a lift with the wheel raised.
- Checking rotational play. The wheel is held and the driveshaft is turned by hand back and forth: noticeable angular movement with the wheel stationary is a direct sign of a worn joint.
- Inspecting the boots. A torn inner joint boot is often the cause of the wear that follows: the grease left, the dirt arrived.
- Checking the fit in the hub. A loose or under-tightened hub nut accelerates spline damage, and it is the first thing checked.
- Separating it from the CV joint. Circles on a car park at full lock: rattling in the turn is the joint, a click in a straight line as the drive changes is the splines — the joint’s own signs are in signs of a worn outer CV joint.
The general catalogue of sounds tied to taking up drive is on the symptom page knocking when accelerating.
What it gets confused with
| Source | When it appears | Character |
|---|---|---|
| Driveshaft splines | Change of drive, pulling away, reverse | Single click at the wheel |
| Outer CV joint | Tight turn under power | Chattering rattle, grows with angle |
| Engine mount | Pulling away, drive–reverse | Dull thump from the centre of the bay |
| Anti-roll bar link | Bumps | Dry knock in time with the bumps |
| Engine | Follows revs, not drive | Sound from under the bonnet, audible parked |
The last row is an important fork. If the knock follows engine revs rather than the moment of pulling away, it is a different story altogether — engine sounds like a stretched timing chain, or in a bad case worn bearings. Separating the groups is simple: stand still and blip the throttle in neutral — whatever is audible then has nothing to do with the driveshafts. A dull thump from the centre of the engine bay belongs to engine mount failure.
How the repair is decided and how urgent it is
It is worth thinking about causes, not only consequences. Splines rarely wear by themselves: they are usually helped along by a torn boot that let water and sand into the joint, an under-tightened hub nut, wheelspin and hard launches. So when a driveshaft is replaced it pays to check the state of the other boots and the hub nut torque at the same time — otherwise the new part follows the same script.
Two questions worth asking. Whether the hub nut will be tightened to the specified torque with a torque wrench rather than an impact gun — that single item decides whether the new joint lasts. And whether the wear was found on the shaft, in the hub, or both: if the hub’s splines are damaged too, fitting a new shaft into them simply moves the problem.
The urgency depends on how much play there is. A barely audible click when pulling away leaves a few thousand kilometres, but that is no reason to forget it: the wear accelerates itself, because every impact enlarges the clearance. A distinct double knock with a jolt is a reason to go to a workshop this week.
If the sound is occasional and you are not sure it repeats specifically as the drive changes, record a couple of pull-aways in the Pro-Stuk app. It matches the sound with the description of the regime and shows the likely causes with percentages — and helps you explain to the mechanic exactly when it happens.
