In general, driveshafts are a bespoke component, individually designed to suit the particular make and marque of vehicle.
To get a perfect and safe fit, every time, a driveshaft must be measured in its fully compressed state but there are a number of reasons you can’t simply visually gauge the correct length by comparing it to the old one.
The ends of the component are packed with grease, the component could be sprung; a worn unit will have a lesser spring effect giving it a shorter appearance.
Take into consideration that once the old part has been removed, the properties of the rubber of the boot mean it will try and revert to its original size, making the new unit appear longer than the old one.
The easiest way to get a correct measurement is to stand the driveshaft on its end, push down hard and then measure.
Other measurement considerations
Check the spline count on the joints; the number of splines will help decide if this is the right application.
Ascertain whether the part has a centre bearing or not and check if it is a one piece with a single shaft, or a two shaft piece with a joint in the middle.
Determine if the part is to be fitted on a vehicle with Anti-Lock Braking (ABS) and if so, how many ABS teeth it has or does it have magnetic pick up.
Keep in mind
Generally, a driveshaft is bespoke and has been designed to suit a particular application to ensure it is capable of handling the power and torque that the particular vehicle can produce.
There are instances where a part number will have multiple applications, but this is mainly due to motor manufacturers sharing common parts like Volkswagen, Audi, Seat and Skoda V.A.G.
Although the length of driveshafts can vary significantly, the diameter of the bar isn’t so much of an issue in the majority of cases as the strength comes from the quality and grade of the steel used.
In very rare instances a driveshaft bar can snap, which results in damage to the parts in the peripheral area as it continues to rotate, especially if being driven at speed, such as suspension parts, the sump or even the gearbox.
These parts would then have to be replaced which could be costly and labour intensive.
Evidence of fatigue can sometimes be seen by the bar starting to twist–generally this is due to the component being subjected to having more power transmitted through the drive-train than was originally intended; for example, if the engine power has been increased.
Worn inner or outer joint–you will experience an intense vibration, or knocking or clonking noises, or scraping or rattling form under the car that will get progressively louder.
Changing the driveshaft can often be a cheaper, quicker and easier way of curing the problem rather than changing one joint only to find that the other joint is worn; especially when you factor in the labour time.
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