CTP TECH
InTheGarageMedia.com
Man in a Classic Truck Performance shirt holding a custom aluminum driveshaft with U-joints in an auto shop environment.
The Tube That Handles The Torque
Measuring for and Installing a Custom Driveshaft
By Ryan Manson Images by Rob Fortier
W

hether you’re building a classic truck from the ground up or performing an engine/transmission swap, chances are you’re going to get to the point where you need to measure for a driveshaft. This can be a stressful time for the uninitiated as any mistake can mean the difference between getting it right the first time or buying another driveshaft after getting it wrong. The crew at Inland Empire Driveline Service (IEDLS) knows the trouble folks can have when it comes to properly measuring for a driveshaft and have put together a simple form that makes ordering a custom driveshaft a simple affair—provided one can read a tape measure.

One of the most important aspects of measuring for a driveshaft is to take the measurements as described by the driveshaft shop. Different shops may use different approaches, so always be sure to check with your local driveshaft shop if you decide to go that route. For us, our go-to has been IEDLS as we’ve found their instructions to be simple and the directions easy to follow. Their measurement sheet gives specific points to be measured and after a couple minutes under the car, that sheet can be emailed to IEDLS and a week or so later a custom-made driveshaft shows up at the shop. It doesn’t get any easier than that. And if there’s any question regarding yoke size or material recommendations, the knowledgeable staff at IEDLS are eager to please.

While we’re slowly working toward making Editor Fortier’s C10 road worthy, the big-block is in place, backed by a 4L70E, and the Strange Engineering 9-inch Ford rearend is hung and ready to rock as well. Looking to tackle another item off the to-do list, we decided to measure for a driveshaft and have the guys over at IEDLS spin us up one of their aluminum masterpieces. It turned out to be one of the easiest things we’ve knocked off the check list as of late, hopefully setting a precedent for things to come!

Technician using a Husky digital level to measure the angle and pinion of a custom four-link truck suspension or rear differential.
1. Before any measurements are made, the angle of both the output shaft of the transmission and the yoke of the rearend are checked and compared, with the truck sitting on the ground at ride height. We’re looking for a couple degrees down at the trans and an opposite reading at the yoke.
Hands holding a measuring tape to size the output shaft and seal of a transmission, essential for custom driveshaft measurement and high-performance driveline work.
Close-up of a tape measure on an exposed transmission output shaft.
2-3. With any necessary alignment changes made, we can now measure for driveshaft length. First, we’re going to measure the diameter of the transmission output shaft, tooth count, and length of stick out from the end of the tailshaft housing.
Mechanic tightening a yoke nut on the transmission output shaft using a large chrome wrench, essential for installing a custom driveshaft.
4. Measuring the diameter of a round shaft with a tape measure can be awkward at times. A quick test to determine if your measurement is accurate is to grab an open-ended wrench of the corresponding size to use as a poor man’s caliper. It won’t split a few thou, but it will tell you whether that shaft is 1-3/4 or 1-13/16 inches.
Technician measuring the yoke flange of a high-performance rear differential using a tape measure, crucial for custom driveshaft ordering.
Technician accurately measuring the flange width of a high-performance rear axle yoke with a Stanley tape measure, critical for selecting the correct U-joint size.
5-6. Next, our attention is moved to the yoke of the rearend. Here, we need to determine the cap diameter and width between the two tabs of the yoke to determine what U-joint needs to be used when IEDLS fabricates our driveshaft. Our trusty tape tells us that we have a cap size of 1-3/16 and a width of 3-5/8 inches, which corresponds to the larger 1350 U-joint. This is to be expected as our C10 has been upgraded with a Strange 9-inch Ford rearend.
Technician using a tape measure to determine the required driveshaft length, measuring from the transmission output seal to a midpoint on the chassis.
Close-up of a tape measure being used to determine the diameter of the transmission output shaft seal for custom driveshaft fitment.
7-8. With the little but important details out of the way, it’s time to measure for length of our driveshaft. This step is very important to be done precisely as the driveshaft shop requests. The distance needs to be measured from two specific points and if this is taken incorrectly, a bad day will be had and the driveshaft shop will be upset to scrap the driveshaft, but happy to charge you for another one. IEDLS requires the length to be measured from the end of the transmission output shaft to the centerline of the U-joint on the rearend yoke.
Mechanic installing a custom aluminum driveshaft underneath a classic truck on a lift, part of a high-performance drivetrain upgrade.
9. IEDLS can fabricate a custom driveshaft from several different materials, from steel to aluminum and even carbon fiber. Manufactured from custom-drawn 6061-T6 DOM tubing with similarly forged weld yokes, our aluminum driveshaft is light in weight but heavy in strength, reliability, and performance. IEDLS’s products have passed Spicer’s grueling dynamic reverse torsion fatigue testing, qualifying them as one of a very few Spicer-authorized aluminum driveshaft builders in the world.
Close-up of a new driveshaft yoke being slid into the tail shaft of a transmission, showing the oil seal and splines during installation.
10. In addition to providing the diameter and spline count of the transmission output shaft, we also noted the make and model of said trans for further confirmation of spec. Installation onto the output shaft is firm and reassuring; a perfect fit.
Technician aligning and installing the driveshaft U-joint yoke onto the rear differential flange of a performance truck with coil-over shocks.
11. Out back, the 1350 U-joint is slid into the rear yoke.
Mechanic using an orange rubber mallet to carefully tap the U-joint yoke of a custom driveshaft into place on the rear differential flange.
12. The U-joint needs to be fully seated into the rear yoke before the U-bolts can be tightened. Here, a mallet is used to lightly tap each cap until it’s securely in place.
Close-up of a newly installed propeller shaft connecting to the rear end of a truck, showing the U-joint caps and differential cover.
13. The U-bolts need to be tight but not overbearing! A torque rating of 20-24 ft-lb turns out to be spot-on.
Close-up view of a new or custom driveshaft with a U-joint connecting to the rear of a transmission, positioned above a stainless steel exhaust system on a vehicle undercarriage
14. When installed, the slip yoke needs enough clearance to not bottom out on the transmission as the suspension travels. This stickout is usually between 1/2 to 3/4 inch and allows the slip yoke to move fore and aft on the output shaft without crashing.
Full view of a custom aluminum driveshaft installed on a classic car or truck, connecting the transmission to the rear differential, seen from underneath the vehicle on a lift
Undercarriage view of a classic or custom vehicle on a lift, showcasing a bright aluminum driveshaft, dual stainless steel exhaust system, and rear suspension components
15-16. With the driveshaft installed, the truck is raised in the air to allow the rear suspension to achieve full droop and to check for any interference.
Document providing instructions on how to measure a one-piece driveshaft, including diagrams for U-joint measurements (D and E) and an example showing X and Y measurements for a 4L70E transmission and Ford 9-inch Strange Eng differential
17. IEDLS makes it easy to succeed in measuring for a custom driveshaft thanks to their concise instruction sheet. With only a handful of specs, IEDLS can fabricate a custom driveshaft, box it up, and ship it your way, without fuss or aggravation.

Inland Empire Driveline Service
(800) 800-0109
iedls.com
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