Street-rodding a long-wheelbase vehicle presents a builder with several new challenges. Among these are shaft length, space constraints, and frame obstacles. The simple solution to such challenges is the two-piece driveshaft. With this revelation in mind, we turned to driveline expert Greg Frick of Inland Empire Driveline Service to give us the straight scoop so we might share this knowledge with our readers. Frick had a perfect example in mind and stepped up to the plate to share his wisdom without hesitation.
The example in question is a '40 Lincoln Zephyr convertible coupe. When it was new, the Zephyr had a Flathead V-12 engine, a three-speed column-shift transmission, torque-tube driveshaft, and Ford's ubiquitous wishbone and transverse leaf-buggy suspension. Work on the car had been started in the 1980s and abandoned in 1986; in 2002, it arrived in the driveway minus its V-12 and transmission.
The car was pulled apart as far as it would come apart. Zephyrs were unibody cars, giving ours a large presence on the rotisserie. In one of the accompanying photos, the very small tunnel for the torque tube can clearly be seen. If a fat one-piece 'shaft was even feasible, major surgery to the floor and tunnel would be necessary. A two-piece 'shaft allowed Frick to plan for the 'shaft-tube diameter similar to the torque tube, and enabled him to leave the floor in its original configuration.
Stance is important to all street rodders. When building a car, it is mandatory that the frame be set on jackstands as it is to run down the road. Doing this ensures that all other parts can be installed as they are to run. Since all angles are relative to the ground and not the frame, a mistake here can ruin your car's drivability. In the Zephyr's case, the Mustang-style frontend was built into the car and a dummy rear axle was mounted on a pair of Eaton Detroit Spring parallel leaves.
At this point, Chassis Engineering motor mounts could be welded in place. The engine was set at 3 degrees down at the rear, as is OEM practice. The company was also able to get the blueprinted 454 from Myron Cottrell at Tuned Port Induction Specialties low enough in the frame for Ken Mogi's TH400 to clear the floorpan.
Next, a really beefed-up 10-bolt rear axle replaced the dummy. Chassis Engineering set the pinion angle at 3 degrees up to produce parallel lines through the pinion and crankshaft. The fun really began at this point-there was a crossmember where the driveshaft needed to be.
This crossmember turned out to be a blessing. It was located in an ideal place for the driveshaft center-support bearing, but it had an oval opening for the torque tube. A little work with the torch produced a flat bottom that the crew plated over and reinforced. To determine how much to cut out, they installed a dummy driveshaft set at 3 degrees down, just like the engine. They also allowed a little extra space for adjustment farther down if necessary, and arrived at 3 degrees using shims.
Using this geometry resulted in equal, opposite working angles of 3 degrees on the rear shaft. Having zero angle at the transmission end can reduce U-joint life there, but it will also move all working angles and their energy well away from the transmission. This is especially important if you are using an overdrive automatic transmission in your project.
The two-piece driveshaft has many advantages in a long car. Much less work goes into modifying one crossmember than into modifying the floorpan, tunnel, and seat bottoms. The two-piece will run smoother than a long, fat, single piece and is much safer than an under-engineered, small-diameter single 'shaft.
The decision to shift from one- to two-piece driveshafts requires careful judgment. The decision will involve the weight of the car, the planned power, tire adhesion, distance between the transmission and pinion yoke, available clearance for 3.5- to 4-inch (or larger) diameter tube, and potential driveshaft rpm. While there are published guidelines for shaft length at various rpm, no hard and fast rule applies to all projects. As soon as you know the distance between the transmission and pinion yoke, a serious talk with a really competent driveshaft shop is in order. Sometimes the choice of design is obvious, as it was in the 125-inch-wheelbase Zephyr. Other times, the decision may be borderline, so let safety be your guide in these cases.
It just so happened that Greg...
It just so happened that Greg Frick was in the process of outfitting a '40 Lincoln convertible with a two-piece driveshaft, so we took a peek at how he went about it.
The Lincoln came equipped...
The Lincoln came equipped with a very small tunnel for the original torque tube setup. Major surgery to the floor and tunnel would be necessary if a fat one-piece 'shaft was even feasible. A two-piece shaft allowed Frick to plan for driveshaft tube diameter similar to the torque tube and enabled him to leave the floor in its original configuration.
When building a car, it's...
When building a car, it's important that the frame be set on jackstands at its desired ride height (as shown here while an MII IFS system is being installed). Doing this ensures that all other parts can be installed as they are to run. Since all angles are relative to the ground and not the frame, a mistake here can ruin your car's drivability as well as its stance.
Correct pinion angle is critical....
Correct pinion angle is critical. Here, the guys installed the engine with the required 3-degree downward slope from front to rear of the engine.
Again, just as correct pinion...
Again, just as correct pinion angle is a must, the rearend requires a matching 3-degree upward slant-opposite that of the engine/trans.
The Lincoln had a huge crossmember...
The Lincoln had a huge crossmember that was cut out for the original torque tube. Frick plated it and fabbed a flat support for mounting the center bearing for the new two-piece driveshaft setup.
Here you can see the center...
Here you can see the center bearing in place in the newly reworked crossmember, as well as one half of the new two-piece driveshaft being test-fit.
A two-piece driveshaft in...
A two-piece driveshaft in a long-wheelbase vehicle will run smoother than a long, fat single piece and is much safer than an under-engineered, small-diameter, single one-piece shaft.
A serious talk with a competent...
A serious talk with a competent driveshaft shop is in order as soon as you know the distance between the transmission and pinion yoke. Sometimes, the choice of design is obvious, as it was in the 125-inch wheelbase Zephyr. Other times, the decision may be borderline, so let safety be your guide in these instances.