CJ-7 Strange Vibration

[Rescue Diver]

Ever since I built my CJ7 and got it on the road a few months ago I've had a weird vibration happen once in a while. It'll be purring along smoothly down the road and when I hit a small bump, all of a sudden it has a small vibration that feels like it's coming from the drive train. It will continue until I come to a complete stop, and then it's gone when I start moving again. It doesn't do it very often, and it always starts when I hit a small bump. I think it might be coming from the rear driveshaft, which was rebuilt by Inland Truck with new U-joints and the slip joint doesn't have any extra play in it.

I have a 4" spring lift. I lowered the cross member 1" a few weeks ago to see if reducing the drive shaft angle would help, and the vibration seems to be a little less noticable, but it still happening. I just ordered a pair of axle shims to tilt the rear yolk up and reduce the driveshaft angle even more. They're on back order, so it'll be a couple more weeks before I can install them.

My problem is, I don't really even know if it's the driveshaft angle that's causing it, or why it would just be intermittent? I've had two previous CJ7 's that were lifted 4" without any driveshaft angle problems or vibrations. When it first happened I thought I might have a loose wheel, but they're plenty tight. Could it be coming from the AMC20 Transfer Case or spider gears in the rear axle maybe???? If so, why would hitting a small bump trigger it?

I just don't get why it would only start doing it when I go over a small bump in the road, or why it would stop doing it after stopping and taking off again.

Has anyone else on here ever had the symptoms I'm describing? It's really driving me nuts trying to figure it out!

 

[DHugg]

Ever since I built my CJ7 and got it on the road a few months ago I've had a weird vibration happen once in a while. It'll be purring along smoothly down the road and when I hit a small bump, all of a sudden it has a small vibration that feels like it's coming from the drive train. It will continue until I come to a complete stop, and then it's gone when I start moving again. It doesn't do it very often, and it always starts when I hit a small bump. I think it might be coming from the rear driveshaft, which was rebuilt by Inland Truck with new U-joints and the slip joint doesn't have any extra play in it.

I have a 4" spring lift. I lowered the cross member 1" a few weeks ago to see if reducing the drive shaft angle would help, and the vibration seems to be a little less noticable, but it still happening. I just ordered a pair of axle shims to tilt the rear yolk up and reduce the driveshaft angle even more. They're on back order, so it'll be a couple more weeks before I can install them.

My problem is, I don't really even know if it's the driveshaft angle that's causing it, or why it would just be intermittent? I've had two previous CJ7 's that were lifted 4" without any driveshaft angle problems or vibrations. When it first happened I thought I might have a loose wheel, but they're plenty tight. Could it be coming from the AMC20 Transfer Case or spider gears in the rear axle maybe???? If so, why would hitting a small bump trigger it?

I just don't get why it would only start doing it when I go over a small bump in the road, or why it would stop doing it after stopping and taking off again.

Has anyone else on here ever had the symptoms I'm describing? It's really driving me nuts trying to figure it out!

Yep! 1980 CJ7 w/AMC 304 engine. After a bit of crawling around underneath, I discover two spring clips missing from the AMC20 yoke-U-joint cradle. When I accelerate from stop, the U-joint slides about 1/8 to 3/16ths to one side, making a slight vibration and barely audible noise.

Got the stuff to repair, permanently, but hate to take it out of service to repair it. Gonna drill out the yoke screw holes and install u-bolt hold-downs, new u-joint and spring clips.

 

[Rescue Diver]

Yep! 1980 CJ7 w/AMC 304 engine. After a bit of crawling around underneath, I discover two spring clips missing from the AMC20 yoke-U-joint cradle. When I accelerate from stop, the U-joint slides about 1/8 to 3/16ths to one side, making a slight vibration and barely audible noise.

Got the stuff to repair, permanently, but hate to take it out of service to repair it. Gonna drill out the yoke screw holes and install u-bolt hold-downs, new u-joint and spring clips.

Do you mean clips like those that hold the U-Joint in the drive shaft? As far as the Transfer Case yolk, I don't see how spring clips could even be installed? The u-joint is held firmly centered in the yolk by the two tabs that stick out, and I have two brand new straps that seem to hold the u-joint tightly against the yolk. I've checked and re-checked the u-joints at both the Transfer Case end and the axle, and found no play.

Or am I misunderstanding what you're talking about?

 

[mylittlecj5]

Sounds like a slight case of Death Wobble to me.
Do a search on 'Death Wobble' and see if it fits your symptoms. Then we can help you repair the root causes.

 

[Rescue Diver]

Sounds like a slight case of Death Wobble to me.
Do a search on 'Death Wobble' and see if it fits your symptoms. Then we can help you repair the root causes.

I'm 99.9% sure it's not coming from the front end or steering. It tracks perfectly straight on the highway at any speed and the steering wheel doesn't vibrate. It seems to be coming from the somewhere between the Transfer Case and the rear axle. It's more of a vibrating buzz than a wobble. It doesn't shake the whole jeep. It's just a vibration you feel in the shifter, and your seat.

 

[DHugg]

Do you mean clips like those that hold the U-Joint in the drive shaft? As far as the Transfer Case yolk, I don't see how spring clips could even be installed? The u-joint is held firmly centered in the yolk by the two tabs that stick out, and I have two brand new straps that seem to hold the u-joint tightly against the yolk. I've checked and re-checked the u-joints at both the Transfer Case end and the axle, and found no play.

Or am I misunderstanding what you're talking about?

You have it right. I see the tabs, but the part I'm hearing and feeling is not "U-joint held firmly centered in the yoke". I can move the U-joint laterally by hand. It is either too small a u-joint or else spring clips needed.

My Jeep has been set up for rock climbing, probably out West somewhere, since there is virtually no rust anywhere, but a few rock scars on the pumpkin, the axle housing, the gas tank shield, front drive shaft, and a few other places. That means I can't count on there being "factory OEM" stuff anywhere.

Keep after it! I have creaks and groans from the front end that will take me a couple years to track down.

 

[Rescue Diver]

You have it right. I see the tabs, but the part I'm hearing and feeling is not "U-joint held firmly centered in the yoke". I can move the U-joint laterally by hand. It is either too small a u-joint or else spring clips needed.

My Jeep has been set up for rock climbing, probably out West somewhere, since there is virtually no rust anywhere, but a few rock scars on the pumpkin, the axle housing, the gas tank shield, front drive shaft, and a few other places. That means I can't count on there being "factory OEM" stuff anywhere.

Keep after it! I have creaks and groans from the front end that will take me a couple years to track down.

My first though was to check the u-joints to make sure they weren't moving around on me. They're tight, and given the fact that it only happens once in a while when triggered by a bump in the road, and then it clears up after a brief stop, I'm at a loss. An off center u-joint wouldn't center itself again every time you stop. It really has me stumped. Maybe it'll go away when I install the wedge shims between the axle pads and springs to take away some drive shaft angle, but if that's the cause, I would think it would vibrate all the time?

 

[ThisGuyUKnow]

Id check your bolts between your tc and tranny and also make sure your tranny mount is tight.... If its coming from the rear end there isnt awhole lot of stuff to check and you say its not the u joints so I would just keep moving forward. Did you make sure they balanced your drive shaft?

 

[Rescue Diver]

Id check your bolts between your tc and tranny and also make sure your tranny mount is tight.... If its coming from the rear end there isnt awhole lot of stuff to check and you say its not the u joints so I would just keep moving forward. Did you make sure they balanced your drive shaft?

Good suggestion on checking the Transfer Case to tranny bolts. I'll take a look.

The driveshaft was balanced after they shortened it. If it were out of balance it would vibrate all the time, and more at higher speeds. This vibration happens even at slow speeds and only intermittently after hitting a bump in the road. I've built a lot of vehicles from the ground up in my life like this one and I've never been so stumped by a small problem.

 

[CJim7]

Pinion bearing.

 

[Rescue Diver]

Pinion bearing.

I thought about that one too, but it spins smoothly and doesn't seem to have any play. I changes the gear oil in the rear diff and the old oil had no metal in it.

 

[CJim7]

I thought about that one too, but it spins smoothly and doesn't seem to have any play. I changes the gear oil in the rear diff and the old oil had no metal in it.

Did you check out the wheel bearings? I recall having one go out...but as I was trying to figure out what the heck the weird vibration was, it would come and go intermittently

 

[Rescue Diver]

Did you check out the wheel bearings? I recall having one go out...but as I was trying to figure out what the heck the weird vibration was, it would come and go intermittently

They're nearly new and spin smoothly.

 

[CJim7]

Rear output on the xfercase?

...just grabbing at straws.

 

[Rescue Diver]

Rear output on the xfercase?

...just grabbing at straws.

The though has crossed my mind but how to check? Like all the other bearings, unless it feels rough turning or has play in it, the only way to eliminate them would be to replace them one bearing at a time without knowing if they're bad. I hope it doesn't come down to that! I would think a bad bearing would vibrate most or all of the time though. I can drive from one end of the city to the other without any vibration at all, and then I'll hit some random bump in the road and it'll start doing it again. I keep thinking it's got to be the u-joints or rear drive shaft, but I'll be damned if I can find anything wrong. I wish I could borrow a drive shaft to swap for a week and see if it goes away, but it'd be a miracle to find someone with a spare of the correct length to loan out. As it is, I had to buy a shaft that was too long and pay to have it shortened and re-balanced.

 

[CJim7]

The though has crossed my mind but how to check? Like all the other bearings, unless it feels rough turning or has play in it, the only way to eliminate them would be to replace them one bearing at a time without knowing if they're bad. I hope it doesn't come down to that! I would think a bad bearing would vibrate most or all of the time though. I can drive from one end of the city to the other without any vibration at all, and then I'll hit some random bump in the road and it'll start doing it again. I keep thinking it's got to be the u-joints or rear drive shaft, but I'll be damned if I can find anything wrong. I wish I could borrow a drive shaft to swap for a week and see if it goes away, but it'd be a miracle to find someone with a spare of the correct length to loan out. As it is, I had to buy a shaft that was too long and pay to have it shortened and re-balanced.

Remove the rear driveline and drive it around in 4wd hitting as many bumps as you can until you're sure it's not coming back. The only problem with this is you aren't applying torque to the rear output or the pinion...so if it's related in any way to those two things, you wont know until you install the driveline again.

One thing to mention is if you are getting vibration from an incorrect driveline angle, the bearings wont last long. So if you are getting intermittent vibration, the bearings will definately show a bunch of wear. You might start there first.

 

[dslywalker]

Read this thread see if it helps
Diagnosing Death Wobble and Fixing Non-DW Shimmies and Wobbles - JeepForum.com

 

[Rescue Diver]

Read this thread see if it helps
Diagnosing Death Wobble and Fixing Non-DW Shimmies and Wobbles - JeepForum.com

Like I said before, it's not death wobble, or any other kind of shimmy in the front end. It's a drive train vibration coming from the center to rear of the Jeep.

I just checked things over again. The bolts are tight between the Transmission and Transfer Case . I pulled the drive shaft again and verified that the needle bearings are fine in the u-joints, and the u-joints fit snuggly between the yoke tabs and are held down firmly by the u-bolts, so there is no way they can be sliding off center. I'm at a loss. Since the vibration, when it happens, isn't as severe since I lowered the cross member one inch, I'm back to thinking it's being caused by the drive shaft angle. I can't explain why it only does it once in a while and why a bump in the road would trigger it?

Guess I'll find out for sure, if it goes away after I install the axle wedge shims, if they ever get delivered.....

 

[dslywalker]

Like I said before, it's not death wobble, or any other kind of shimmy in the front end. It's a drive train vibration coming from the center to rear of the Jeep.

I just checked things over again. The bolts are tight between the Transmission and Transfer Case . I pulled the drive shaft again and verified that the needle bearings are fine in the u-joints, and the u-joints fit snuggly between the yoke tabs and are held down firmly by the u-bolts, so there is no way they can be sliding off center. I'm at a loss. Since the vibration, when it happens, isn't as severe since I lowered the cross member one inch, I'm back to thinking it's being caused by the drive shaft angle. I can't explain why it only does it once in a while and why a bump in the road would trigger it?

Guess I'll find out for sure, if it goes away after I install the axle wedge shims, if they ever get delivered.....

I was referring to the non-DW vibration part of this thread

 

[bdunnam]

well this may sound dumb but do you have new hub lockouts? I had a very similar vibration after i replaced mine with new ones, but i just ran it and it quit after bout 3 or 4 months.