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Working with our friends at JE Reel Driveline, we put together a completely custom driveshaft for our 1950 Chevy Fleetline, Project Tiger’s Eye. Having taken care of the shorty exhaust system the last time around, let us tell you about the custom driveshaft and educate you about how they are made, and optimal build points.

With Tiger’s Eye well on its way, we’re building from the ground up to ensure we don’t miss a step. Continuing our search for a new shell, we are diligently working on the Fleetline’s internals to build out a solid driveline that boasts power and reliability.

Driveshaft Anatomy

Jim Reel at JE Reel Driveline explained there are three different types of driveshafts based on end attachments, including reverse slip, standard slip, and constant velocity. Each shaft fits different applications, so measurements are necessary to determine the proper one.

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A driveshaft helps to relay torque and rotation within a drivetrain setup. Relative movement on both ends is needed to make the driveshaft operational. The science behind it all is that the driveshaft serves as a torque carrier, where it is exposed to stress and torsion from the drivetrain.

The determining factor for the proper driveshaft is to have an angle up front and to not starve the rearend.
– Jim Reel, JE Reel Driveline

Driveshafts function to bear the stress from the engine while being light in weight to avoid increasing inertia. In order to allow for differences in alignment and distance between the functioning components, the driveshaft integrates one or more joints to help make the driveline function properly. The sole purpose of a driveshaft in a car or truck is to deliver power from the engine and transmission to the opposite end of the vehicle before its translated to the wheels.

“In a reverse slip application, the slip yoke simply slides into an automatic transmission or newer style transfer cases,” Reel said. “When measuring, the only point of reference you need is for the rear U-joint only. When dealing with reverse slip, you simply have to measure the spline diameter, seal inside diameter, and carefully count the spline.”

Determining the spline count and the attachments on each end between your transmission and the rearend are essential.

Standard slip driveshafts operate in a slightly different way. “The standard slip is where the spline is welded into the end of the tube, and the slip is part of the driveshaft,” Reel said. “It slips in and out as the rearend moves up and down. It’s a solid bolt-up at each end between the transmission case and transaxle.”

The constant velocity (CV) slip is a unique configuration that is only called up during special circumstances. “The CV slip is similar to the standard slip driveline, it’s different in that it utilizes a double cardan or CV joint at the ends,” he said. “It bolts up with ease and there are some that use an uncommon style where it slides in and out of a slip yoke on an automatic transmission. It’s usually some kind of modification.” A custom driveline depends on power and length to set the parameters of what is acceptable in a specific application.

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A look underneath prior to the driveshaft installation.

Measuring Perfection

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Diagram courtesy of JE Reel Driveline.

Choosing to focus on hot rods and drag cars, Reel went into great detail about how to measure from the transmission output shaft to a third member. “The best way to measure is to slide in the automatic transmission yoke and bottom it out,” he said. “You measure from the center of the U-joint eye back to the edge of the yoke. With that bottomed out, subtract one inch off of that measurement, giving you enough room to push the driveline forward to get the joint out and remove it for service without it binding on anything.”

The next way to measure would be from the tip of the spline to the edge of the yoke or flat face of the flange. “We tend to measure from the seal to the edge of the spline, where there are a lot of variables,” he said. “In a Turbo 400 transmission, some of the yokes stick out an inch where it won’t fit properly if it is too long.”

Reel explained that information regarding how long the free bore inside where the yoke is becomes vital when making specifications for the proper application. “Other points of advice when designing and developing a custom driveline involve knowing the amount of horsepower and length of the driveshaft,” he said. “The length of the tube will determine the diameter of the tube to prevent it from whipping and blowing itself apart.”

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A closer look at the spline on a 700R4 automatic transmission.

In the case of hot rods, Reel said they tend to build shorter drivelines if they are designed to be show cars. “However, in the case a rodder wants to get on the gas, a bigger diameter tube is needed to handle the RPM range,” he said. “High-end RPM is not as important in a hot rod build, but if the driver is sitting at a given RPM for long periods of time, the car is going to have trouble.” Once the proper measurements are made and end attachments are determined, the next step is to find the target pinion angle.

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Once the measurements are determined, it is time to size up for length and pinion angle to ensure the driveshaft is not dead level with the U-joint.

Target Pinion Angle

Typically, an engine is sloped down four to five degrees in the back. “The pinion should match within two degrees of being parallel,” he said. “When it is parallel and is dead level, it wears out the U-joints within a couple hundred miles. You simply have to have some downhill drop in the driveline.”

Reel suggested a driveline have at least a 0.5-degree drop to ensure that through each revolution, the rearend attachment cancels out the first vibration from the front. “The maximum operating angle for a U-joint is three degrees in order for it to run the smoothest as well as have the longest life,” he said. “Since older cars were long and low, like Lincolns and Cadillacs, the engine was down. With the pinion being down as well, it created dissecting angles instead of parallel angles, leading to CV joints put in place on each end of the driveshaft.”

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The slight pinion angle up front is key to getting the most out of the rearend while also increasing the longevity of the driveline over time.

When searching for the target pinion angle in a CV joint configuration, Reel recommends pointing the rearend as close to the center line of the CV as possible. “The determining factor is to have an angle up front and to not starve the rearend,” he said.

Lining It Up

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Installing the custom driveline was fairly simple and didn’t cause any problems. With our measurements made, we received a driveshaft designed specifically for Tiger’s Eye’s drivetrain, and everything fit nicely. The 1310 series driveshaft that was custom-built specifically for Tiger’s Eye is capable of handling 400 to 500 horsepower applications.

The maximum operating angle for a U-joint is three degrees in order for it to run the smoothest as well as have the longest life.
– Jim Reel, JE Reel Driveline

The key was to attach the front of the driveshaft first, followed by lining it up with the rearend. Using our Bendpak two-post lift, we easily fit the driveshaft in with basic hand tools. Linking the rearend to the 383 cubic inch small-block Chevy mill and B&M 700R4 transmission with a driveshaft that is capable was our primary focus, which JE Reel graciously built just for this project.

Given we are working with a Fleetline sedan, the driveshaft is a bit longer compared to the coupe. The install was fairly simple, and with more driveline work to accomplish, it brings together another piece to the puzzle.

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After tightening the driveshaft to the rearend, the all was said and done.

Finding What’s Right

All in all, the driveshaft made for great fitment and is sure to help us generate a solid driveline when Tiger’s Eye is fully operational. Sitting down with Jim Reel, we gained insight on what it takes to build the proper driveshaft for a given application. With no standard version that fits the norm, the guys over at JE Reel are meticulous in designing and building what is right for you.

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There’s still plenty left to do up top, but we were pleased with the fitment of the driveshaft beneath.

“Power thresholds and length should always be taken into account to go along with the measurements on both the front and rearend,” Reel said. “From hot rods and dragsters heavy-duty off-road applications, our driveshafts are designed to perform for each application accordingly.”

With our drivetrain setup now linked, we can pursue our other aspirations for Tiger’s Eye. There is still plenty to accomplish with the build, but we were glad we didn’t experience any problems installing the driveshaft beneath. Unobtrusive and with plenty of room, the driveshaft from JE Reel fit seamlessly.

Stay tuned as we continue to bring Tiger’s Eye back to its former glory. To view the latest updates on this build, be sure to visit the designated build thread.

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