As automotive enthusiasts, most of us are familiar with the parts needed to make an engine more powerful, a transmission shift harder, or even the rear axle gear ratio required for maximum acceleration. But what about the link between the transmission and the rear end, the driveshaft? Because the driveshaft can't really enhance the performance of our vehicle we often forget about it, just assuming it will do its job until something bad happens. And when bad things happen to a driveshaft, yoke, or universal joints, your drive can get disastrous in a hurry. At the very least, a driveshaft problem will leave your vehicle stranded, and at worst can lead to transmission and rear end damage, or loss of control of the vehicle. For these reasons, the driveshaft is one part of a Mopar where preventive maintenance pays off.
As you'll see in our Hidden Treasures column this month, we recently purchased a groovy '78 Dodge Tradesman 200 California show van. As a running and driving vehicle, we made the trip from Ft. Myers, Florida, back to Lakeland, Florida, without much incident in our new purchase, but noticed a moderate vibration coming from the van's drivetrain. While driveline vibrations can have a variety of sources, experience told us that this vibration was coming from either the driveshaft, transmission or pinion yoke, or one of the universal joints.
It's really no surprise that problems occur with the prop shaft, or driveshaft of a vehicle, especially one that's used in a high-performance application or hauls heavy loads. Every time you drop your car into gear or let the clutch out, the driveshaft is absorbing the torque of the engine and transferring it to the vehicle's differential. Each time you accelerate or decelerate, the driveshaft and its related components are loaded and unloaded, and it happens countless times during a normal drive. The bearings inside the universal joints take a beating as well, since the driveshaft spins at thousands of rpm each time the vehicle is driven. Add a smoky burnout or two or run over some debris, and the shaft itself can become bent and out of balance, which will eventually lead to universal joint failure or premature wear of the pinion bearing of the rear end, or the output shaft bearing or yoke bushing of the transmission.
In our case, we weren't sure what was causing the vibration in our van as the universal joints seemed to be tight and in serviceable condition. While under the van, however, we did notice several dents in our driveshaft indicating it could have been damaged by road debris. Since the driveshaft spins at a relatively high rate, a bend in the driveshaft can cause a pretty severe vibration which can only be repaired by straightening and rebalancing the shaft, or re-tubing the driveshaft altogether. With this in mind, we pulled the driveshaft from the vehicle and took it to our local driveshaft shop, Central Florida Driveshaft, to have it repaired.
Once at Central Florida Driveshaft, the staff placed our shaft in one of their driveshaft lathes to check it for straightness and balance. Spinning the shaft on the lathe, it was quickly apparent that our driveshaft was severely bent and would require major repair. In some instances the shaft can be straightened, but in our case the driveshaft would have to be cut apart and rebuilt with a new tube. Fortunately, Central Florida Driveshaft has new driveshaft tubes, ends, universal joints, and even yokes to make repairs easy. For our driveshaft they recommended replacing the tube, and to save us a few bucks they offered to use a second-hand tube that was in good shape. In addition to rebuilding driveshafts, most driveshaft shops can shorten, rebalance, and repair driveshafts in addition to installing new universal joints. On other project vehicles we've even had them make a driveshaft from scratch based on our measurements.
1 We picked up this ’78 Dodge...
1 We picked up this ’78 Dodge Tradesman van as a cool driver and inexpensive alternative to typical A-, B-, and E-Body Mopars. The van’s 360 runs good, and the vehicle is in overall great shape, but we noticed a driveline vibration that needs to be addressed before it causes damage. Narrowing the problem down to the driveshaft, we decided to pull the shaft and take it to our local shop, Central Florida Driveshaft, to be rebuilt.
2 Always set the parking...
2 Always set the parking brake to keep the vehicle from moving—or in our case, a wooden block. Remember that “park” gear will only hold the vehicle if the driveshaft is in place. Also, place a drain pan under the transmission tailshaft to catch any transmission fluid once you pull the slip-yoke out.
3 Having an extra 727 slip-yoke...
3 Having an extra 727 slip-yoke around is helpful as it can be installed to prevent leaks and to keep dirt from getting in the transmission while the driveshaft is being repaired. This is one we shattered in one of our race cars, but it still works for our purpose here.