By: Joe Micciche. May, 2001.
Long wheelbase Toyota 4WD trucks are equipped with a two-piece driveshaft, which has a variety of parts and measures just over 65" long. These two-piece driveshafts have u-joints at the transfer case output and at the pinion, but in the middle is a center support bearing (CSB) and a double-cardan joint. A significant benefit of this design is offroad clearance: the forward section of the driveshaft is near-perfectly horizontal to the ground to the CSB, and only the rear section is angled down from the CSB and double-cardan to the pinion. However, it is this collection of additional parts - particularly the CSB - which aggravates many Toyota owners.
|The very long factory two-piece driveshaft.||The center support bearing and double-cardan joint.|
The CSB is a bearing encased in a rubber shroud. Over time, the rubber degrades from road and trail debris, and the bearing begins to wobble in the shroud. This manifests itself in driveline vibrations, and requires a new CSB.
After installing 2" lift springs, I immediately experienced driveline vibrations, plus a slight clunk when letting off the throttle. I first checked the CSB, which had approximately 1/4" of play in all directions: the CSB was getting worse with time, since before the spring install it had 1/8" play. Because there is no definitive statement about how much play is acceptable, I decided to live with this and continue diagnosing.
With the help of Scott Wilson's Driveline Basics article, I began checking the driveline angles. The two-piece shaft ensures the forward u-joint angle remains static regardless of lift, but determining the proper angle at the double-cardan and the rear u-joint proved more elusive. With some help, I determined that the pinion needed to be shimmed up 3 degrees (allowing for some tip while under load - 4.5 degrees appeared to be optimal) so that it would point at the double-cardan and create the proper angle.
|A cap on the rear u-joint cracked.||The CSB allowed the driveshaft to rotate in an ellipse.|
So I installed the 3 degree shims, and unfortunately they did not cure the vibration, but they just changed the frequency. In the meantime I kept driving the truck and checked everything in the suspension, when I noticed the CSB had grown to nearly 1/2" of play. The driveline also developed a hum, so I parked the truck.
I discussed options with numerous people and priced out Toyota CSB's. It quickly became apparent that the CSB would likely wear out again over time, necessitating another replacement: and with one Toyota CSB priced just below a whole new driveshaft, the solution was very obvious...
|South Bay Driveline One-piece Driveshaft|
|The one-piece unit is much simpler than the factory two-piece.|
Steve Johnson at South Bay Driveline was quite helpful when I inquired about a one-piece driveshaft. For my application, Steve suggested what amounted to a Chevy half-ton driveshaft: he only required the measurement between the transfer case output flange and the pinion flange to begin building the new driveshaft. Three days later, the new driveshaft arrived!
The new SBDL driveshaft is a 3.5"-diameter 0.083"-wall tube, with Dana-Spicer 5-625X u-joints at each end. At thirty pounds, the new driveshaft weighs approximately half what the stock two piece driveshaft weighs, and is a much simpler and more reliable design. The tube necks down to a slip yoke with nearly 6" of useable slip built in.
Prior to installation, I rechecked the driveline angles. Because I was moving from a u-joint / double-cardan driveshaft to a u-joint / u-joint driveshaft, the transfer case and pinion flanges needed to be on the same plane. With the 3 degree shims installed, the pinion was tipped up too high, so I removed the shims and remeasured. This netted u-joint angles within 0.5 degrees of one another, which is close enough to the optimal zero-degree difference that no shimming was required.
|The CSB support was torched out, but the frame crossmember retained, to increase driveshaft clearance.|
Installation of the driveshaft was simple and quick - because the transfer case output and pinion flanges on my '94 Extracab had the exact same pattern as the Dana-Spicer yokes. (Ordinarily the flanges must be removed and drilled out for the Dana-Spicer pattern.) We began by removing the CSB dust shield, then removed the four 14mm hex head flange bolts from the transfer case output. We supported that end with a ratchet strap, then removed the two 14mm hex bolts from the CSB carrier; and finally removed the four bolts from the pinion flange. With some mild persuasion, the old driveshaft was freed and discarded. It was during this removal that we also discovered a broken rear u-joint cup, which did not help the vibration problem at all.
While the driveshaft was off the truck, I also checked the pinion nut for proper torque, which is 145 ft. lbs. on my '94 AT. There was no sign of runout either. Ordinarily this should be done early on when diagnosing driveline vibrations.
The new driveshaft was fit into place and new, longer flange bolts were used to accomodate the thicker Dana-Spicer yoke. The u-joints and slip yoke were then greased, and the truck was ready for a trial: as expected, all problems were eliminated! Additional benefits resulting from this swap include more "responsive" power application due to the elimination of the CSB, double-cardan, and weight; and the price and availability of spare parts should they ever be needed.
|The SBDL one-piece driveshaft installed.||The front 5-625X u-joint.|