Jim Smart
August 1, 2001

Driveshafts do a big job in our Fords, Mercs, and Lincolns. They take a powertrain's rotary motion and carry it to the differential and drive axles. This is not an easy task. Not only must a driveshaft transmit rotary power without failure, it must articulate with the up-and-down movement of the rear axle as we cruise over highs and lows in the road. Highs and lows range from smooth transitions to really rough ones.

We visited Inland Empire Driveline (IED) for a closer look at driveshafts, universals joints, and yokes. What we learned from IED applies to every one of our readers out there, so listen up. Even if you're building a restomod with stock driveline components, you need IED to get you on the right track with Spicer universal joints and yokes. This ensures the kind of driveline integrity you need and want for drivers and show cars alike. And when it comes to the driveline, there are no unimportant parts.

If your Ford has a two-piece steel-over-rubber driveshaft, which was popular during the '60s, with automatic applications to absorb vibration, we suggest having a new shaft made. These vibration-absorbing shafts have deteriorated over time to where they're prone to the very thing they were designed to prevent: vibration. IED can make for you a new precision-balanced, one-piece shaft for vibration-free operation.

We're having an aluminum driveshaft made for a '67 Mustang with C4 Cruise-O-Matic and a Gear Vendors (GV) Overdrive unit. This calls for specialized driveshaft fabrication by the experts at IED. Because the Gear Vendors Overdrive unit is 14 inches long, this makes our C4 14 inches longer than it was in stock form. We've measured our application and have concluded our shaft needs to be 37 inches from center to center (universal joints). Pinion angle at the differential will have to change to accommodate the shorter driveshaft. We're going to show you how to do this later in the article.

How A Driveshaft Is Made
IED has our driveshaft specifications nailed down. We need a shaft that's 37 inches center to center. Tom Aragon of IED is going to custom-make an aluminum driveshaft for us designed for a '67 Mustang with GV Overdrive. We'll then show you how to install and set up the shaft.

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How To Measure For A Custom Driveshaft
When we measure for a custom driveshaft, our measurements must be executed with close attention to detail. It's here that we suggest redundancy, because mistakes can be costly. Few things are more frustrating than having to have an expensive driveshaft made all over again. A shaft that's too long won't clear the differential yoke for installation. What's more, it can bottom out in the transmission, causing internal damage. A shaft that's too short can be hazardous and even pop out. Ideally, the front yoke will slide back and forth one half to three quarters of an inch when properly dimensioned. Remember the old carpenter's axiom: "Measure twice, cut once."

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Joint Effort
Universal joints are what enable a driveshaft to articulate smoothly with the transmission and rear axle in all kinds of conditions. To function properly, we have to have the right-size universal joint. Here are the most common types. Not shown are U-joints with two different-size widths and caps for special applications. IED can help you there too.

A: This is a Spicer 1350 with 1 3/16-inch caps.
B: The 1330 Spicer U-joint has 1 1/16- or 1 1/8-inch caps.
C: This is the 1330 Spicer with coated 1 1/16-inch caps for aluminum shafts.
D: The 1310 Spicer U-joint has 1 1/16-inch caps and is common to early Fords.


Spicer transmission yokes from IED come in three basic sizes: 1350, 1330, and 1310. If you're in doubt about the yoke you need, talk with the professionals at IED for fast answers and even faster service.

We measure universal joint size at the points shown in the accompanying illustration. Use these measurements when ordering parts from IED.

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Angle of the Dangle
Whenever we lengthen or shorten a driveshaft, we have to consider driveshaft angle. Driveshaft angle must be the same as the crankshaft and transmission output shaft for proper function. IED sells a special instrument for this purpose called a magnetic protractor. The magnetic protractor mounts on the differential pinion magnetically, which tells us the pinion angle. It also attaches to the transmission tailshaft housing to determine the angle there too. If pinion angle isn't the same as the transmission tailshaft angle, the rear axle must be shimmed fore or aft to correct pinion angle. We change pinion angle by rotating the rear axle fore or aft around the housing's lateral axis (axle flange to axle flange).

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Driveshaft Troubleshooting Facts
IED knows Jack when it comes to driveline woes. They're here to help you based on solid tried-and-proven experience in more than 20 years of business. Here are some valid pointers.

  • Never overtighten the differential-yoke U-bolts. When you overtighten, the cap may compress the needle bearings, causing friction and premature wear. Proper torque for most U-bolts is 14-17 lb-ft (1 1/16- to 1 1/8-inch caps) and 20 lb-ft for 1 3/16-inch caps. With the naked eye, this is tightening the nut until the lock washer is flat, then giving it one eighth of a turn tighter.
  • Make sure you have the right-length shaft. With the vehicle on the ground, the transmission yoke should show three quarters to one inch of polished surface. If you have to jack up the car to install the shaft, the shaft is too long.
  • Vibration is caused by several things. With the vehicle on a hoist, check the universal joints for side play. No motion, of course, is good. Side play (joint sliding back and forth in the caps) between .0005 and .0015 inch is normal for greaseable universal joints. Excessive side play can, and does, cause vibration.
  • A dent in your driveshaft can cause vibration.
  • Driveshaft runout between .000 and .012 inch is acceptable. Anything beyond .012 inch is cause for replacement.
  • Whenever vibration sources cannot be determined, remove the driveshaft, run the engine, and put the transmission in gear. If the vibration persists, the cause is not the driveshaft.
  • If vibration occurs under hard acceleration only, the pinion angle needs to be adjusted. Move the pinion angle downward one half to one degree, then road-test.
  • If vibration occurs during deceleration, move the pinion angle up one half to one degree and road-test the vehicle.
  • If you're experiencing driveshaft ringing whenever you're shifting gears or putting an automatic in gear, the shaft can be filled with foam or cardboard by IED which will silence the shaft. Do not attempt to do this yourself.
  • If runout is found at either end of the shaft, try rotating the shaft 180 degrees (one-half turn) and road-test the vehicle. It will either get better or grow worse. If it's worse, see IED for help.

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