Hey all...
First off, truck is a '93 W250, 4WD, 12V Diesel.
Truck has 1 ton axels, and 4 inch lift.

Here is the issue:

Under light driving conditions, I have no problem. Basically keeping the boost under 4 PSI. However, it doesnt matter what speed I am at, anywhere from 10 to 70 MPH, if I start to put my foot down at all, the entire truck starts to shake violently. If I back off the throttle, it goes away.
Under light or no load conditions, there is no problem. Putting the truck in 4wd doesnt affect it at all.

So far, I removed the rear drive shaft. I checked the u-joints on both ends, both have fresh grease and move perfectly. The slip yoke also has grease and slides no issue there. Nothing seems loose either.

With the DS out, I grabbed the input flange to the rear diff. I wiggled it around in all directions, I could feel no play here.
I did the same to the transfer case. There was some play in the circular direction, but nothing that seemed abnormal. I believe it is chain driven, so I little movement would be expected.

I took the truck out for a drive with no rear DS installed. For some reason I could hardly keep it on the road... or get my speed up... I think I may have an alignment issue. However, when I put my foot into it, there was no shake.

So, all in all, I know I have an issue somewhere between the transfer case and the rear wheels. Unless the DS is completely out of balance, then it can be ruled out, and I think that would be noticeably all the time.

Can anyone tell me what could be causing this? I dont know what else I can check without tearing things apart, which I dont want to do at all if I dont have to. For reference, the rear axel is a DANA 70 with power lock.
The lift kit isnt that high, so the angle in the DS doesn't seem very excessive.

Any advice at all would be very helpful. Thanks!

 

How's the rear trans mount?

BTW, your NP205 transfer-case is gear-drive.

 

Rear mount looks good and solid. I havent tried putting a jack under it but it looks fine.
Here is an odd thing. I just went out and lay down in the snow. I put the jack under the rear diff and lifted the whole rear axel up in the air. (the DS is still off) I then rotated the one tire, and both turned together. I then went underneath and turned the flange on the diff. Both wheel appear to be locked together through the diff... I cant get one to stop rotating or for them to move independently from each other... there is absolutely no play through the diff to the wheels... but it seems odd. I dont know if the Power-Lok is supposed to work this way... or if someone has modified the rear end... or if possibly the locking diff is stuck on?? ANy thoughts?

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Ok update:

I got stuck on the front lawn... 6 inches of snow and no rear wheels ... i got mad and threw the rear drive shaft back in... I still had the rear end in the air so I started her up and ran it through the gears... everything felt good. I left it in gear spinning and walked around the truck... looked good, good DS alignment. Put it back on the ground and took her for a rip... it was perfect! It was smooth as can be! I dont know what was going on before, but something was obviously misaligned or something... I changed nothing... I didnt mark the DS position, so it is possible it is 90 degrees from where it was but thats it... it drove like a champ!

Thanks for all the input! Seriously... im very pleased right now.

 

If both axles are in the air both axles will turn. Have you tried putting the rear in the air and wiggle the rear wheels to check the inner and outer axle beatings.

 

Just for later grins & giggles, get a video of the next time you do that. . . . . . . ya know. . . . just in case.

Going back and re-reading your original post, you're not very clear as to whether the issue just appeared out of the blue, or immediately after some work on the truck.

Your description of simply removing the rear drive-shaft, and then later reinstalling it with positive results suggests one of the universal joints was out-of-phase . . . ?

 

Hey, I actually only bought the truck about a month ago, and I have been restoring it. I just finished the body and painting it, and am moving onto the mechanicals to get it to pass safety. The “death shake” was there since I test drove it, and I assumed it was a bad u-joint from the beginning.

The only other thing I could think of is that people talk about the slip yoke getting dry and causing problems. I greased the hell out of it and it didn’t fix the problem, but once I removed the DS from the truck, I slid the slip yoke through its full range of motion, and this may have distributed the grease better. Not sure if this makes sense.

But at the end of the day, it had to have either been the slip yoke, or a u-joint either out of phase, or possibly out of alignment or not centered.

 

I'd throw a jack under the tranny and make sure the mount is good

 

Hey guys, here is an update...

To restate, My truck is a ’93 Ram with the Cummins. Rear axle is a DANA70. 4” lift, and no rear leafs at all, just air springs.
I have been having a pretty heavy vibration in the rear end. I did a full drive line check. Removed rear DS and found nothing wrong. Drove the truck with no rear DS, everything seemed good. (no vibes) When I put the shaft back in, the vibes were cut in half, but still there. It only occurs under load, and at any speed.

Since my truck has no leafs in the rear, I can use the air bags to control the rear height by 2 or 3 inches. There are additional frame members which are in place to handle the torque etc... however I have been running the air bags at minimum pressure for a smoother ride. What I noticed is that when the air bags are low, the axle will be closer to the frame, which will force the pinion angle to be a little steeper. By increasing the pressure, the air bags lift the body and frame off the axle, thus changing the angle on the DS.
Also, with more air, the suspension becomes tighter, which is going to resist axle wrap, and lesson the likelihood of the diff flexing under acceleration. This change in angle seems to reduce the vibes quite a bit.

I went out for a drive, and I think it made it a lot better with additional air in the sacks. I took pictures of the rear u-joint so you can see the difference in angle. Whether the air bags are full or empty, the pinion angle really doesn’t seem to be very excessive, so what I think I will do is replace the u-joints in case either of them are damaged from the vibrations, and try driving with the bags a little more full from now on. The u-joints felt and looked good when I had the DS out. I was hoping some of you might be able to tell me how my angles look… I am wondering if the change in angle with full springs is just treating the symptoms of a bad u-joint or if I am hitting some sort of critical angle. The pinion bearing and T-case bearing feel good.

Here are the pics I took:

This is with the bags empty, the way I have been driving:

http://i1279.photobucket.com/albums/...ps30fef7e0.jpg
And this is bags full:

http://i1279.photobucket.com/albums/...psa97b769a.jpg
Im hoping it could be as simple as this... not sure if my logic makes sense... I would love some second opinions.. I tried to indicate the change in angle as best I could.

Thanks.

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In case the links dont work, here they are again:

http://i1279.photobucket.com/albums/y539/jdschwass/20130324_141432_resized_zps30fef7e0.jpg
http://i1279.photobucket.com/albums/y539/jdschwass/20130324_141222_resized_zpsa97b769a.jpg

 

look at the connecting links to the suspension. looking at the pictures, it looks like you are running a 2 link, ladder bar style, setup, is there a track bar to help eliminate side to side axle movement? are there any other link bars triangulating theirselves to help center the axle and eliminate side to side movement?

who made the kit? is it an off the shelf kit or a homebrew kit?

 

I am not really experience when it comes to lift kits, it is not something I have ever put on a truck. My buddy looked at what I have and said it was a 4-bar… the axel has 2 parts connecting. One goes forward and pins on the frame, and the other looks like one solid leaf spring that goes forward and pins onto a drop-down shackle. On the rear side there is an extra shock added to buffer any axle rotation.
To prevent side to side movement, there is a bar that looks like a sway bar. It connects to both ends of the axle (solid, articulating like a sway bar) and then has to brackets that go upwards and mount it solidly to the frame. This limits vertical movement and suspension travel, but holds the axle firmly in place.

The kit looks like a professional kit. All the parts are well built and identical. It shows no signs of a home-job. That being said, I don’t know who makes it because I didn’t put it in. The springs/air bags are Firestone I believe.
I don’t think the kit is causing my issue. The front axel is lifted the same amount, so there shouldn’t be a large difference from stock in the drive line, apart from the fact it may be more prone to flexing.

What do you think of the change in drive line angles? Do either seem excessive?