I have been chasing a vibration starting at about 68-70 mph. The drive shaft has been rebuilt twice, u joints twice and tailshaft bushing. Entire axle assembly rebuilt about 2000 miles ago. I had found a few things in the front suspension that took some time to resolve. I have had a little spare time lately and completed that work.
So with the front suspension tightened up, a subsequent test drive had a slightly different vibration feel. This lead me back to the drive shaft. On stands, engine running, in drive I could see the front end of the drive shaft wobbling. Shut it down and found I could move the driveshaft yoke around .030" +. I thought how did the tail shaft bushing wear out so fast?
Pulled the extension housing out and the bearing looks new. I will be taking it to the shop to put our inside micrometers in the bushing to see what size it is. Although, when I slide the bushing and housing onto the removed drive shaft yoke there does appear to be much clearance.
When investigating, as I would try to move the yoke in the housing, it actually looked like the yoke was pivoting on the bushing. The yoke itself has a hollow unsplined ID for about 1.5" before the female spline starts. With the extension housing removed, I can move the output shaft around .060" in all directions.
OD of yoke looks good but I will measure that as well. I have no other tranny symptoms. Is that too much shaft movement with the housing off? I will report further after measuring the above mentioned parts.
Well I have measured the ID of the tailshaft bushing at 1.690" with inside micrometers. With calipers, I measured the slip yoke OD at 1.685" to 1.687". I will be taking my 1-2" micrometers home to measure further. However this looks pretty good even with the caliper measurements.
The exploded views I have seen show a bushing in the forward end of the output shaft. I can see where if this was a little worn you could move the other end quite a bit. Also, I keep seeing a “spline seal” shown in between the yoke spline and the speedo gear. Mine has a steel clip that slides up and down the shaft between the speedo gear and the yoke spline.
I had an F150 that had a mystery vibration that turned out to be wear on the inside of the yoke. I had the transmission rebuilt and the rear axle rebuilt as well as the drive shaft. Nothing helped. I sold the truck for cheap since it had this mystery vibration. The guy that bought it replaced the yoke and it solved the entire issue.
There is only one tailshaft bushing, just forward of the seal. .005" clearance sounds about right. I would be suspicious of the forward driveshaft yoke like Bill said. New ones are available and not terribly expensive.
There is a spline seal like you say, and it was not available when I rebuilt my C6 last year. Sounds like yours is missing. Mine was like new so I kept it. I think this is an item that may have to be purchased used. Not sure it is the cause of your trouble.
I would think that seal used just to keep fluid from leaking out on the assembly line. Then when the driveshaft gets installed it gets pushed in. Similar to the lolly pop so many people have found that seals the dipstick tube hole.
Check your slip yoke for hour glass shape from wear.
I will be checking some things out today. Being in the spline business I have a few tools to use yet. The first is that the drive shaft is not original and has to be inspected on the yoke end further as I haven’t determined if it is even correct.
One thing I will check for is wear as mentioned above. With the unknown slip yoke I will also be checking for the proper type of fit. By that I mean “side fit” or “major diameter fit.” Many yoke splines, male splines that mate with slip yokes, are major diameter fit. In this case we roll the major diameter (OD) oversize and grind the major diameter back down after heat treat for concentricity. The female spline major diameter is then broached to a tolerance of about .001". Side fit splines do not touch each other at the major diameter.
I can tell my yoke spline on the shaft is not major diameter fit as it is not ground on the OD. When using major diameter fit, we allow more backlash as the OD is controlling the fit and run-out. Side fit splines have much less backlash and it is the fit of those teeth that control the backlash and run-out.
So if I have a major diameter fit slip yoke, I will get a new proper one ordered. If I find wear I will order new as well. If my measurements prove to be OK. I’m going out of the box to try a couple of things. I will not just throw a new slip yoke in there without some data as they say. My main concern for awhile was the slop in the output shaft with the extension housing removed.
Hello all,
I have completed my spline inspection and found no significant wear in either yoke spline. Our internal devices could not measure deep enough for the entire length of the internal spline. Our internal major diameter could not reach deep enough either.
I decided to put it back together. Because I could and as an experiment, I installed 6 O rings where the spline seal would be on the shaft. My subsequent test drive showed improvement. However, I would only say it was cut in half or so.
Being that I was able to effect some change I will start looking at slip yokes for purchase. Following my work the wife and I took Pole Cat 45 minutes north for a walk in the woods and visited, from a distance, an eagles nest.
Take care all! I’ll update when I get a new slip yoke. Probably going to be a while.
Hello all,
I have completed my spline inspection and found no significant wear in either yoke spline. Our internal devices could not measure deep enough for the entire length of the internal spline. Our internal major diameter could not reach deep enough either.
I decided to put it back together. Because I could and as an experiment, I installed 6 O rings where the spline seal would be on the shaft. My subsequent test drive showed improvement. However, I would only say it was cut in half or so.
Being that I was able to effect some change I will start looking at slip yokes for purchase. Following my work the wife and I took Pole Cat 45 minutes north for a walk in the woods and visited, from a distance, an eagles nest.
Take care all! I’ll update when I get a new slip yoke. Probably going to be a while.
Hi, Gary. Did you come to a solution for this problem? I’m having the exact same issue entirely. 390-C6 swapped into my 66 LTD. I’ve got the same vibration at the same speeds. I’ve gone over every possible thing I can think of and I’ve traced it down to play in the yoke at the extension housing. I’ve replaced the bushing AND the yoke with still the same amount of play. New yoke measures 1.685 OD. I didn’t measure the bushing myself but it’s listed to be 1.69 ID. I haven’t measured the play at the yoke but it’s certainly not a tight fit, it’s enough to obviously cause the vibration and the seal leaks. I’ve been looking for different yokes or bushings to fit tighter, I’ve found yokes that are listed as 1.685 AND 1.688 OD but under the same part number, so I don’t know If i trust replacing the yoke again. Let me now if you found anything, please and thank you
Could one or more of the u-joint cups be missing a needle? Does a U-joint have excessive play in the the yoke because the yoke was spread open or the tabs on the pinion yoke are worn? Either would cause run-out.
If you have some time, try taking the slip yoke off the shaft. Reinstall it 180 and road test. Or, put the slip yoke on the other end of the shaft. See if it makes any change. Owning a transmission shop I have dealt with many driveline vibrations and have seen slip yokes shaped like an hour glass that did not create vibration. I doubt a new bushing a slip yoke is at fault.
A couple things you may want to check before sending out the driveshaft to be balanced.
U-joint phase angles. This is probably not your problem as you don’t have a drive shaft that that has an integrated slip yoke. These can come apart and be reassembled with one end clocked wrong in relation to the other end. These cause binding issues and vibration. I have seen solid tube drive shafts with the yokes welded out of phase.
U-joint operating angles. Everytime a u-joint flexes under load it sends a vibration wave along the shaft. When both u-joints are at the same angle, the vibrations will meet in the middle and cancel each other out. If one u-joint is working at a steeper angle it’s vibration wave will be strong and the opposing wave will be weak. This strong wave will be felt in the car as vibration. What to look for is: are the tail shaft of the trans and the pinion shaft of the rear in parallel? They don’t need to be in line with each other ------although reducing driveshaft working angles will also reduce the potential for vibration. On my 68 full size Mercs, the operating angle of the rear axle is adjustable via an eccentric on the upper control arm. Perhaps your 66 LTD is set up the same way?
Check for run-out. I’ve seen some drive shafts with a fair amount of run out that didn’t exhibit vibration-----because they were balanced with the run-out. Changing a component will change the run out and take it out of balance-----even though it may be running on a straiter axis.
If the above features appear to be correct. Then I would suggest sending out your drive shaft for spin balancing. A drive shaft shop will say any time any component of a driveshaft is replaced, it should be balanced.
Good Day, Sorry for my delay. I saw this thread pop up a few weeks ago and meant to write. I had been preparing and then went on a two week fly fishing vacation in Wyoming. Now it is back to life.
Anyway, so yes, back in August some time I was finally able to get a new yoke and install. The tailshaft bushing still looked and measured as new. The new yoke ended up at 0.003" max. clearance. This worked out well and the vibration is gone. I believe the old and new yokes are slightly different in the ears but my new one was also shorter in the yoke area as well. About 3/4".
