Forum I'm helping with a rear axle rebuild. The drive shaft, tube and radius rods have been cut for a Muncie transmission that is attached to the fourth main. All of the items came together on a chassis of a 26/7 frame and running gear. It was all together but I'm not sure if it ever ran. So far the Muncie transmission looks good and fairly tight. The drive shaft tube looks professionally done with an excellent weld and is plum end to end. The radius rods are also resized and correct. The previous owner ( deceased ) also had the drive shaft resized and it looks really well done. Now for one of the issues, it appears that the universal joint was free floating. The there is no hole for the pin. We measured and compared the the short drive shaft with a regular size drive shaft and where the the universal slides onto the drive shaft was a perfect match to the regular one with the exception of the set pin hole not being drilled. I should mention the Babbitt bearing has been replaced with a new brass bearing, set and drilled for the grease fitting. Issue two, I know that on a regular rebuild that the universal with the set pin in the universal helps insure that the drive shaft is stationary from the stand point of thrust so you can accurately set the pinion to the crown gear using shims to help set proper lash. Is this something that is different with the accessory transmissions where the universal floats? I can't image that being the case but like I said in the title I don't know what I don't know. Any help from the forum members would be great. Thanks in advance, I await your considerable experience in doing this the right way the first time.
One would have to assume it has a modern pinion kit in it.
Never assume. The Muncie makes no difference concerning the need for the U-joint being pinned to the drive-shaft. There have been several efforts over the years to provide pinion bearing replacements that also provide thrust in both directions. Some have worked well, others, not so much. From everything I have heard about them, John Regan's Fun Projects setup is the best of all. If the pinion bearing does not provide full thrust prevention in both directions, the U-joint MUST be pinned to the drive-shaft. Arguably, even with full thrust prevention in the pinion bearing, the U-joint should still be pinned in place because without it, the U-joint must seek and hold its own angle center. Something it may likely do on its own, or not.
From a problem solving standpoint. The ring and pinion (crown and pinion) thrust and positioning is one problem, and it MUST be solved in one way or another. Ford chose to solve it simply by using the drive-shaft itself and the U-joint for the lesser thrust direction. He used a ball bearing thrust bearing in the greater thrust direction (that of the crown/ring attempting to push the pinion and shaft forward). This easily and coincidentally also solved the U-joint centering problem. However, it is still a separate problem.
Drive carefully, and enjoy, W2
If I remember correctly, even though the Regan bearing handles the thrust in both directions, John says you still want the U-joint pinned.
I seem to recall John saying that in some thread awhile back. However, I do not claim to speak for John R. John R is one of the most intelligent and knowledgeable people I have ever had a discussion with. A lot of us have opinions about these things. John's should be listened to.
John did say that and reiterated it to me personally. His reasoning is straightforward: If the u-joint rotational center moves away from the center of the DS tube ball, vibration, wear and premature failure of the u-joint will result.
He does not recommend using the bronze shaft bushing face as a thrust face for the U-joint, as his kit provides for axial thrust in both directions.