One aspect of modifying a vehicle, that is sometimes an afterthought, is replacing the driveshaft because the original driveshaft no longer fits. Sometimes it’s because you’ve swapped an engine or trans, and other times it’s because you’ve swapped a rear differential, but when your original driveshaft ends up being too long or too short, it becomes time to break out the ruler and tape measure – because you can’t just roll your car down to the shop to have them measure it.

No doubt, if you ask friends or club members you’ll probably find a couple of different answers on how to properly measure the distance between the rear of your transmission to the yoke in the differential. Dynotech Driveshafts has put together a list for instructions that provide you with everything you need to replace your driveshaft.

If you thought that it was as simple as having just one measurement, guess again. You not only need to provide the distance, but they will also need to know the dimensions of the various components that your new driveshaft is going to bolt up to.

When doing the measurements, be sure that the vehicle’s suspension is fully loaded, meaning it must be at ride height.  You can put your car on ramps if you can’t crawl under it, but the measurements need to be taken without the suspension hanging in mid-air.

The first measurement is from the transmission tailshaft housing to the yoke on the differential. This is the distance from the metal part of the housing (not the seal or output shaft) to the face of the pinion yoke. Second measurement is the distance across the pinion yoke where the universal joint sits. This is so they’ll know what size the bearing caps need to be.

The third measurement is the distance between the u-joint saddles. Some yokes might have locating tabs, others won’t, so if you do have tabs the measurement should be to the inside of the tabs. Without tabs, the measurement is the distance between the inside flange of the u-joint saddles. These measurements will help with the sizing for the universal joint itself, and also so they can match the driveshaft yoke to those dimensions.

The last measurement that needs to be made is the distance that the output shaft extends beyond the tailshaft housing. Again, this is from the metal edge of the housing and not from the edge of the seal or bushing. When making this measurement, Dynotech says to note if the output shaft has a threaded hole on the end. And while you’re there, count the number of splines on the output shaft. It may not be as easy as it sounds, so one trick is to use a permanent marker to mark the first spline.

Once all of your measurements are recorded, choosing the material for your new driveshaft is the next step. For most street applications you’ll want to stick with a steel driveshaft, but for racing you might want to choose Aluminum, carbon fiber or a hybrid driveshaft, which is carbon fiber wrapped around an aluminum driveshaft over the chromoly seamless tube steel driveshaft.

If you’ve ever wondered about balancing a driveshaft to remove those unwanted vibrations in the driveline, Dynotech spins the driveshaft up to 8,000 rpm and balances them to less than 0.20oz-inch. They will make your custom driveshaft to within 1/16-inch, and they guarantee that it will fit providing your measurements are correct. So now that you know how to measure for you custom driveshaft, head on over to Dynotech Driveshafts and download their order form and you’re that much closer to getting your ride back on the road.