Last Saturday morning, Doc stopped by Nelda's Diner for his early morning breakfast. Doc was about half way through his flapjacks and maple syrup, when Dabney came into the Diner. Doc looked up from his newspaper to see Dabney. "Why so glum, Dabney?" Doc said.
"Hi, Doc. I got a problem with my '65 MGBGT. I had to replace the universal joints. The old ones were so loose and worn and made so much noise that I couldn't even hear the radio anymore." Dabney sat down and ordered coffee and donuts.
"I got it all back together and all I did was make things worse. When I test-drove the car, as soon as I let out the clutch, I thought the car was going to fly apart...it started vibrating something terrible. This happened in all gears, no matter how fast or slow I was going. Sometimes it vibrated so bad I thought the fillings were going to come out of my teeth. Maybe I put the driveshaft in wrong, but I sure can't figure out how I could do that. I just took it back out and everything looks ok to me. What could be simpler than putting in a driveshaft?"
"Well Dab, old boy, you've got a point," said the Doctor. "You got a fitting at the front end that goes onto the transmission tail shaft, and the usual coupling at the rear to the differential's yoke. Not much you can do wrong there. Although, it's possible, of course to reverse the ends of some driveshafts, and some have welded-on weights at the differential end for balance. Yours isn't like that. What exactly did you do to install the new joints?"
Before he spoke, Dabney went over it in his mind. "I put the shaft ends in my vise and took out the old joints with a hammer and drift. Then I cleaned the sleeve areas, checked for burrs and restrictions, and tapped in the new bearing cups. The cups tapped in pretty easily and went in far enough to get the snap rings into place, so there's no chance one of the needle bearings is jammed at the bottom of a cup, if that's what you think," said Dabney.
"What next?" queried the Doctor, finishing his flapjacks, slurping his coffee and ignoring Dabney's defensiveness.
"Then I put the shaft back in," said Dabney. "What else was there to do?" Nelda brought Dabney's donuts and refreshed the Doc's coffee without asking.
"Jumpin' jackstands, Boy, did you twist the new joints to see if they were tight?" Doc asked.
"Of course I did. How dumb do you think I am?" Without hesitation, Dabney added, "Don't answer that." "The joints moved around, although they were real stiff."
"There's your vibration problem!" said Doc.
"What?" said Dabney. "How could new joints be too stiff? Isn't that the normal way the bearing cups work?"
"Nope, those u-joints should have been nice and loose, without any 'play'" said the Doctor. "The reason your bearing cups made everything stiff is that they weren't perfectly centered in the driveshaft's sleeves."
"But it all went back together so easily. How could it be wrong?" Dabney was totally confused.
"Tell you what, my boy," the Doc said. "Let's finish up here and go over and check it out." Dabney's garage was just across the street from Nelda's, and Doc was starting to feel sorry for Dabney (a rare occurrence).
They finished, paid their tab and Doc continued their conversation as they walked across the street. "You'd think that, because they fit so tight and have to be tapped in, they would be centered, but they can still go in at an ever-so-slight angle, and that's just enough to cause your vibrations," said the Doctor.
As Dabney opened the garage door, he could see that the Doc was getting energized. Must be the coffee kicking in, Dabney thought. "Hand me the driveshaft, Doc ordered as he walked into the garage."
Dabney watched as the Doctor gently held one end of the driveshaft in the vise. He moved the u-joint in all directions. "Yeah, their stiff, all right. But it does feel like you got it all back together OK," Doc mumbled. Using a small hammer, he tapped the shaft's sleeve area all around the bearing cups. After he was sure he had tapped all the way around all the cups, he tested the u-joint and it moved quite freely, with no stiffness and with no play. He then did the same thing at the other end, with the same results.
Satisfied that he was finished, the Doc looked up. "You see, Dabney, all the bearing cups needed was a little help to line themselves up. A little judicious tapping with a hammer creates just enough shock to allow the cups to seat properly. Stick this baby back in there and let's test her out."
Dabney installed the driveshaft. Doc relieved Dabney of the keys and fired up the MG. "I'll drive," he said. Dabney frowned, walked around the car and got in and down the road they went. Of course, there was no vibration. And it was merely a coincidence that they ended up at Doc's place. "Thanks for the ride home, Dab," Doc said with utter sincerity as he got out of the car."