I have a friend whose Mopar mechanical and automotive skills I have great respect for, insists that a driveshaft yoke shoved into a transmission bushing with too much clearance is the root cause of many unexplained intransigenet driveline vibration issues.
He recommends a new bushing which is too tight and honing it out to fit the specific yoke you are using. He suggests with the transmission out of gear to relieve stress on driveline, to attempt to move the yoke up and down. Any permitted movement is indication of potential problem.
I will forward this thread to him for comment.
As my friend is not a member of this forum but he did send this response to me after I had forwarded a copy of this thread to him. The following is a "copy and paste" of his response.
Roger:
It looks like you explained it well but I'm happy to provide you something you can cut and paste as I am not a member there. However some members on this site may carry over to the FBBO forum and would recognize me by my handle Meep-Meep.
The sign of slip yoke vibration is to drive the car close to or at freeway speed and find that spot where you "float it" by not being under power or deceleration. Just modulate the throttle until you hear that grumble sound and you will find you are not loading the drive line, thereby allowing the yoke to rattle around in the tail housing. This is independent from a balance issue since an out of balance shaft will try to orbit around it's center of mass even with a properly fitted bushing.
It's been my experience lately with slip yokes that the clearance is way too loose even when replacing the parts with new. And by way too loose I mean over about .007" is too loose. For a quick test on an unloaded drive line (tranny in neutral and rear wheels off the ground) grab the front yoke and attempt to move it up and down and you should have little to no perceptible motion. I don't have the actual dimensions off the top of my head but for sure the new yokes that I measured are small and the bushings are perhaps bigger than they should be. My yoke reference is taking the measurement on the non worn part on a factory yoke. One car I had measured over .060" and others are in the .020" range if memory serves and all have the grumble to some varying degree. Granted taking a dial indicator measurement way out at the U joint will show a pretty big number but it's still a reference.
The fix is to fit the bushing to the yoke with the proper clearance, and since the yoke is the part more likely to be replaced or changed, it would make sense to make an undersized custom bushing and hone it to fit the new yoke. For honing I will take my next tail shaft and yoke to a machine shop that has the Sunnen hone like the kind used to resize rods and tell them it's like fitting a piston pin (but not piston pin clearance). This will ensure a non tapered round bore. The only catch is the bushing bore needs to be in proper alignment with the output shaft bearing all the way up to the pilot bearing or front pump bushing.
Alex Lobodovsky
