Converting a Driveshaft

Ball and Trunnion to Slip Yoke

Background

An issue for both stock and performance A, LA, B, and RB Mopars running a 1962 – 1965 TorqueFlite 727 transmission is the antiquated ball-and-trunnion driveshaft design. All 1962 – 1964 TorqueFlite transmissions, like their cast-iron TorqueFlite and PowerFlite ancestors, used a splined output shaft with a yoke flange bolted onto the end. The flange yoke on the driveshaft bolted to this transmission flange yoke followed by a ball-and-trunnion joint (Figure 1). Some 1965 TorqueFlites maintained this design, but in 1965 Mopar moved to a design where a slip yoke slides on the output shaft splines (Figure 2), familiar to many people more so than the ball and trunnion design. For stock cars, the ball and trunnion rebuild and replacement parts are becoming difficult to source along with driveline shops willing to take on the project; for performance cars, the ball-and-trunnion coupled with its smaller driveshaft tube is an inherently weak design compared to slip yokes with 1350 or 1410 series universal joints. A ball and trunnion that breaks can have devastating effects to both a vehicle and driver when the front of the driveshaft digs into the road if not equipped with a driveshaft loop, so an upgrade is wise, which I detail below.

Mopar Ball and Trunnion Driveshaft Diagram
Figure 1: Mopar Ball and Trunnion Driveshaft Diagram (Typical for 1955 – some 1965 models)
Mopar Slip Yoke Driveshaft Diagram
Figure 2: Mopar Slip Yoke Driveshaft Diagram (Typical for 1965 onward)
Converting from Ball and Trunnion to Slip Yoke

There are two options for 1962 – 1965 TorqueFlite transmissions to go from ball and trunnion to slip yoke:

Option 1: Swap in a 1965 A/LA/B/RB slip-yoke output shaft and tail housing.
While a relatively straightforward-sounding option, the swap requires taking the transmission completely apart, replacing the output shaft, and installing all the transmission parts within tolerance adjusting thrust washers as necessary, which may be out of the realm of mechanical ability and/or affordability for some people. Aside from the cost of new gaskets and having someone perform the work if one cannot himself/herself, donor slip-yoke 1965 727s are becoming difficult to locate and expensive since they have been sought after by racers since their invention due to the slip-yoke. A reader might ask, “Why not just swap in any slip-yoke 727 output shaft and tail housing from 1965 – 1989? Why only 1965?” 1963 – 1965 727s include a separate cable-operated parking pawl that works a sprag fastened to the output shaft (Figures 3 and 4). (1962 727s while cable operated did not have a parking provision on the output shaft). 1962 – 1965 727s also had a rear pump located in the front of the tail housing with provisions for the inner gear and governor on the output shaft (Figure 5). 1966 – 1989 slip-yoke 727 output shafts and tail housings do not have the necessary provisions for the rear pump and cable-operated parking and, therefore, do not interchange. After the conversion, one would have to have a driveline shop build a new driveshaft to replace the ball-and-trunnion unit.

Option 2: Maintain the stationary flange yoke on the transmission output shaft and build a slip-yoke driveshaft using quality parts such as Spicer.
Having a driveline shop add a slip-yoke into a new driveshaft is likely the most affordable and easiest way to delete the ball and trunnion and is just as strong as converting the transmission to a slip-yoke output shaft. The output shaft conversion detailed in option 1 requires a new driveshaft anyway, so the slip-yoke addition means having to pay for two additional parts: the front flange yoke and the midship shaft I detail in the next section, although the cost of the midship shaft is partially offset since it replaces the front tube yoke.

TorqueFlite 727 Pushbutton Cable Operated Parking Pawl Lever
Figure 3: Cable-operated TorqueFlite 727 Parking Pawl in the Tail Housing
TorqueFlite 727 Pushbutton Cable Operated Parking Sprag and Rear Pump Governor
Figure 4: Cable-operated TorqueFlite 727 Parking Sprag and Rear Pump Governor on Output Shaft
TorqueFlite 727 Pushbutton Cable Operated Rear Pump
Figure 5: Cable-operated TorqueFlite 727 Rear Pump
Building a Slip-yoke Driveshaft

I have done a great deal of research on the parts necessary for a slip-yoke driveshaft and confirmed the design with my local custom driveline shop that ended up building my driveshaft, but some variables come into play with the type of flange yoke on the transmission output shaft and rear end pinion flange that one should confirm independently from the parts I list below since Mopar used different diameter flanges over the years. For example, the 1964 A/LA 727 I’m using in my 1956 Dodge coupe has a flange with 3.75″ bolt center and 3-15/16″ diameter outer lip/curb which limits my options to the weaker 1310 u-joint series flange, so I had to machine off the lip and enlarge the bolt holes in the flange to use a 1350 flange. Another consideration is the u-joint series based off the engine torque and intended use. The factory rear u-joint on most early to mid-60’s Mopars was a Spicer 1310. According to Spicer, the 1310 is rated for 400 continuous ft.lbs. of torque and 800 ft.lbs. of short-term load, such as when starting a burnout or launching off the line. The 1330 is an upgrade, but the flange dimensions and price make the argument to go straight to a 1350 rated for 1,240 continuous ft.lbs. torque and 1,680 ft.lbs. short-term load, which is plenty strong for the vast majority of cars/trucks putting out up to 600 TQ. For the most serious racers, the 1410 is an option. The last consideration is driveshaft tube diameter and gauge. Many ball-and-trunnion Mopars used a 2.5″ tube, which is fine for stock configurations but weak for performance builds compared to a 3″ x .083″ wall tube. If one desires a 2.5″ or 3.5″ tube, flanges are available.

In the build sheet below, I include the rear flange yoke to go from a 1350 u-joint to a Ford 8.8″ rear end I am using in the 1956 Dodge, but rear ends such as the Mopar 8.75″ and Ford 9″ do not require an additional flange yoke since the u-joint secures to the pinion flange.

Parts List from Transmission to Rear End:

  • Front Flange Yoke (to bolt onto the transmission output flange): Spicer 3-2-119 (1350 series, 3.75″ bolt center, 4 bolt holes at .438″ diameter, 2.75″ male pilot hole, Figure 6)
  • Front Universal Joint: Spicer 5-178X (1350 series, Figure 7)
  • Slip Yoke: Spicer 3-3-488KX (1350 series, 1.5″ diameter x 16 female spline, 7.312″ from center joint to end, Figure 8)
  • Midship Shaft: Spicer 3-53-1531 (1.5″ diameter x 16 male spline, 6.58″ long splines, for 3″ x .083 tube, Figure 9)
  • Tube: 3″ x .083″ (long enough with the vehicle level on the ground to allow the midship shaft to slide into the slip yoke 1″ before bottoming out for rear suspension movement)
  • Rear Tube Yoke: Spicer 3-28-57 (1350 series, for 3″ x .083″ tube, Figure 10)
    • Note: The rear end pinion yoke may require a different u-joint series and needs to be considered when choosing the rear tube yoke.
  • Rear Universal Joint: Spicer 5-178X (1350 series, Figure 7)
  • Rear Flange Yoke: Spicer 3-2-1619 (1350 series, 4.25″ bolt center, 4 bolts holes at .472″ diameter, 2″ diameter pilot, Figure 8)
    • Note: This flange is only necessary when connecting the driveshaft to a Ford 8.8″ or similar rear end with a flat pinion flange.

Flange Yoke Spicer 3-2-119 (casting C3-2-531)
Figure 6: Front Flange Yoke (to bolt onto the transmission output flange) – Spicer 3-2-119 (casting C3-2-531)
1350 Series Universal Joint Spicer 5-178X
Figure 7: 1350 Series Universal Joint – Spicer 5-178X
Slip Yoke 1350 U-joint Spicer 3-3-488KX
Figure 8: Slip Yoke for 1350 U-joint, 1.5″ x 16 Spline – Spicer 3-3-488KX
Midship Shaft Slip Yoke Spicer 3-53-1531
Figure 9: Midship Shaft, 1.5″ x 16 Spline – Spicer 3-53-1531
Tube Yoke for 1350 U-joint Spicer 3-28-57
Figure 10: Rear Tube Yoke for 1350 U-joint – Spicer 3-28-57
Flange Yoke for 1350 U-joint to Ford 8.8 Rear End Spicer 3-2-1619 (casting C3-2-651)
Figure 11: Rear End Flange Yoke for 1350 U-joint (to bolt onto Ford 8.8″ pinion flange) – Spicer 3-2-1619 (casting C3-2-651)