Mysterious Driveline Vibration

You bet. Actually, the pinion is 1 degree lower than the shaft to cover flexing of the rubber suspension link bushings while under cruising load. Maybe it should be more than 1 degree?

/Peter

----- Original Message ----- From: "L.W. (ßill) Hughes III" Newsgroups: rec.autos.makers.jeep+willys Sent: Wednesday, September 08, 2004 10:39 PM Subject: Re: Mysterious Driveline Vibration

disappears.

No more than one degree on a TJ. You only use more when there are leaf springs because axle wrap is a bigger problem for them.

Jerry

So, what else could cause a vibration at higher road speeds?

/Peter

Could your driveshaft be out of sync? Are the u-joints at the ends lined up the same? For instance, if the clamp on the u-joint ear is rotated up in the front, is the rear joint also sitting with the ear clamp up?

If so, then my guess is the driveshaft is a bad one. There are shops around that can balance them.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Peter P>

If the drivetrain angles are indeed correct, it could be anything from a bad u-joint to an out of balance driveshaft. Or tires, or pinion bearings, or... it's really hard to say.

Jerry

It's a Tom Wood's CV shaft, and it hasn't been apart so the yokes are still in phase. It didn't used to vibrate, that started recently.

/Peter

Okay, thanks, I just wanted to make sure there wasn't something obvious that I missed. I guess not, so I'll probably have to get it balanced again. Too bad there's no shops in my city that can do that.

/Peter

It's recent? Different animal then I guess.

Have you given the joints a real close look? It's a double cardan isn't it or is it a real 'CV' joint with ball bearings?

I find our organic mud destroys the 'heavy duty' non grease u-joints in less than a year, are yours like that? If so then I would suspect a dry/burned by the mud cap and bearings on one of the joints.

I test it with tires blocked in neutral so the shaft is floating and look for the slightest play. 'Any' play will cause a vibe.

Good luck.

Mike

Peter P>

It's a "near constant velocity, double-cardan-style universal joint shaft", referred to as a "CV drive shaft" despite having no true CV joint in it. The convention of referring to these things as "CV drive shafts" is so universal that I'm not going to bother quibbling about the terminology. See

for more.

All the joints in this shaft are the greasable type (there's even a fitting for the centering ball) and have been greased regularly. I have the non-greasable stock joints in the axle shafts and the stock front driveshaft, but they haven't needed replacing. I've only had to replace one bad u-joint in the three years I've been off-roading this rig, and it was the greasable type.

Yep, been done with no play. I'll check it again though, just in case.

/Peter

That's exactly what they look like, as shipped by Tom Wood's.

Nope, as mentioned previously this is a Tom Wood's shaft, with all the welded-on balance weights it was shipped with still in place. I'm pretty sure I'd see evidence of broken welds if one of the weights was gone. I did manage to knock the grease fitting for the slip member off a while back and had to fit a new one. I find it hard to believe that that would cause this vibration though.

Well now, that's an interesting idea. What does one do, drill a hole in the tube, toss in a couple shot glasses of ATF, and weld it up again? Would this work in a shaft with only two or three inches of tube?

/Peter

If it was hit hard enough to shear the grease fitting, well.....

I think I would jack up the rear pumpkin, put it in gear and run it like Bill suggests to check for round.

Mike

"L.W.(ßill) Hughes III" wrote:

Will do.

I was just thinking ... is it possible that it is the front shaft that vibrates when running in 2Hi, but doesn't vibrate when under load, i.e. when the rear shaft is removed?

By the way, how was last week's bush run / camping?

/Peter

I was going to mention that. A front axle u-joint will sure act like that, so can a driveshaft one.

The trip was pretty good. Snowboardripper, Jo and Steve showed up. One other came but couldn't get across a big washout solo to get to us. We found a pretty insane trail that got really technical fast. Winches, jacks and snatch blocks. I only cracked my frame, snapped the rad in half and punched out a gas line...

I will get the photos done and make a proper trip report soon unless someone else makes it.

Mike

Peter P>

I just spent a bit of time under the jeep, checking into the things you guys mentioned. The rear shaft sure doesn't look bent, I used the same trick I use when truing bicycle wheels on it, slowly bringing a chunk of oil pastel to the spinning shaft, and it made a complete, even circle agains both the slip member and the tube.

With the transfer case in neutral and the rear wheels in the air, the rear drive shaft doesn't wiggle. However, if I jerk it straight down with a significant portion of my weight, I seem to hear/feel the faintest of clicks but can't see any movement. I can't really tell whether it's coming from the double carden area of the shaft or from the transfer case tail cone, but my money is on it being the bearings in the transfer case. However, what I don't know is whether this is normal or not. It is very slight indeed.

Moving to the front of the jeep, I did notice quite a bit of play in the slip member of the front drive shaft. There is a visible movement, perhaps as much as a couple of millimeters. I'm going to remove the front shaft again and see what happens. I'll keep you posted.

/Peter