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Driveline vibes...

ccarley

ccarley

1/2 ton status
Joined
Aug 29, 2010
Posts
543
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Location
Rohnert Park, CA
Ever since replacing my trans and trans mount, I've got some crazy vibes going on under the truck. Feels like U-joint to me, but I want to describe what I've got going on and see if anyone can say "yup, that's it!".

***I will be replacing both U-joints on the rear shaft today***

So, after fixing the trans and replacing the trans mount, I had a vibe coming on at 50 mph, and worsening at 55 mph. Guessing it was U-joints, I replaced the one after the transfer case, as the one at the rear axle was new, and it was visibly worn out. During replacement, it is possible a needle fell as it was tight in one of the yokes. It felt like it was OK, but it's hard to tell on a lot of the farm roads out here.

Now, it is getting worse again. My wife describes it as a chair massage at 50 mph (I call it a grumble), and it is almost scary at 55 mph.

First thing to check is U-joints for this issue, yes? Would driveshaft angle cause these types of vibes, or would that cause different symptoms? The driveshaft could be out of balance, however I didn't have this issue before, and we are always careful not to beat it or bend it :laugh:

Truck is a '89 Suburban, with 4" spring lift.

Again, I'll be doing the U-joints on the rear shaft today, to start things out.

Thanks,
Clay
 
Some u-joints are not great quality and dont last long when used in lifted trucks,especially if the driveline angles are extreme...it's also quite easy to "lose" a needle when installing the caps,if one lands at the bottom of the cap it is still possible to get the clips on and it'll self destruct in short order..

Also sometimes the u-joint binds up even after proper installation,a few hammer taps on the end of the yoke where the caps go will usually free a stiff one up..

If you have a driveshaft with the splined yoke and fixed yoke on the transfer case and you removed it to install the u-joint,you may not have put it back on so the u-joints are in phase,that'll cause some disturbing noises and binding..
 
So for this description of vibes... U-joint is the first place to look. The driveshaft is one piece, with a slip yoke in the transfer case; I'd rather have a fixed 'case yoke but oh well. There's really no odd noises, just the vibrations.

As far as the quality of joints used, well I do get the Autozone/ Duralast brand joints. Autozone here is nicer than O'Reilly, and the guys behind the counter at my local Autozone at least know what they are talking about. A U-joint replacement isn't that bad to do, now that I torched the OE GM plastic retainers.

Thanks,
Clay
 
I prefer to buy name brand u-joints like Neapco,Wesco,etc,but I did use a Autozone one reluctantly on the front axle joint on my plow truck last winter ,I forget if it was a Duralast or Valuecraft,it was only like 12 bucks....mostly because Autozone is not far away (about 2 miles) and the road conditions sucked at the time...

I had fears of it failing,but so far its holding up OK--if anything the "ears" on the axle shaft are probably going to fail first,they are rusted away and about half the original thickness..I plow with a light foot ,especially when cornering while pushing a full blade of snow,it does that "crab walk" with the wheels cut..

Nowadays I suppose no matter who's name is on the box,chances are it might be of China or other 3rd world origin and not that great a quality...I think I saw "Hench En Mexico" on the Autozone box...:doah:..

Another thought,if this started after doing the tranny mount,not the u-joints,perhaps the mount was over torqued or is made of much harder rubber or something,and is letting vibrations get transmitted into the crossmember..or maybe the angle of the tailshaft was changed?..
 
It's very possible that the angle of the tailshaft has changed. The old mount was so worn out, the new one may be 1/2" higher. The engine mounts are worn as well, and are on the list of things to do. I figured with the length of my rear shaft on the Suburban, the minor change of angle shouldn't be too bad... but I could be wrong.

U-joints are an easy enough change at least. I guess I'll have to find a protractor to check out the angles if the new joints don't fix the issue.

Thanks,
Clay
 
Well, it's never that easy for me!

I pulled the driveshaft, and the U-joints feel nice. No roughness, and tight enough. But I got a protractor app for my phone & checked the angles...

Transfer case: downward tilt of about 3 degrees
Rear axle: upward tilt of about 12 degrees

That seems like the problem right there. So I guess I'm on to motor mounts... and then possibly axle shims.

Clay
 
Most people do not watch the phasing. And if angles are off a little, phasing being out makes it worse.
 
With my rear shaft being 1 piece, the phasing can't get off unless it gets twisted. But that video shows clearly what happens in each case, which is awesome!

I believe that my axle at 12 degrees and my T/C at 3 degrees is causing my problem for sure. I'll be replacing my engine mounts and checking again to see if I need some shims.

Thanks,
Clay
 
ccarley said:
With my rear shaft being 1 piece, the phasing can't get off unless it gets twisted. But that video shows clearly what happens in each case, which is awesome!

I believe that my axle at 12 degrees and my T/C at 3 degrees is causing my problem for sure. I'll be replacing my engine mounts and checking again to see if I need some shims.

Thanks,
Clay
Click to expand...

My suburban engine/trans/t-case angle is right at 4. Why is the rear at 12 deg? Angled block?
 
The rear springs (56", 4" lift from Pro-Comp) do indeed have an angled shim in them. I measured off the flat spot next to the pinion support on the axle; in any case there is hardly any angle on that U-joint. The driveshaft is about 10 degrees, and the pinion is round about 12. With the Transfer Case at 3, there is more angle there than at my axle.

If the rain holds off this weekend, I'll get some pics (and replace the engine mounts). But it's supposed to dump here in Nor-Cal...

Clay
 
There is less operating angle at that pinion joint, and that is what is causing the issue. The way it is now is almost perfect for a cv at the t case.:D
 
Wow, this kept me up last night. I am thinking that changing the engine mounts won't do much for my T/C angle, maybe change it a degree but not that much at all. And the axle sure won't point down on it's own.

If I have to re-bolt the spring pack to install shims, I should measure the shim that's there now... I'll be doing that today.

Clay
 
With my burb, It took having the pinion between a degree and a degree and a half lower than t case, to get cancelled out under load.

Really depends on the springs themselves, but I would shoot for atleast 1 degree lower at pinion than t case.
 
Well, sometimes I am lucky, and sometimes not so lucky. This time it looks lucky.

The wedge at the bottom of the leaf spring is measuring right about 8 degrees, which is what I want to take out. Even better is the fact that these springs are bolted together, and it looks like I should be able to unbolt them still, remove the wedge, bolt it back together. Now, I think I've used up all the remaining good weather here in Nor-Cal this weekend, as it was sunny earlier and is looking like rain now. Yesterday's rain was pretty fun (hard core sideways action!)

Clay

EDIT: Photos

IMG_20150207_092640_649.sized.jpg


IMG_20150207_092651_873.sized.jpg
 
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We finally had a chance to work on this today. Using a protractor app on my cell phone isn't the greatest tool at all. In fact, that is probably the worst protractor ever.

The shims measured out to maybe 3 or 4 degrees when removed (using lame cell app), so instead of removing them I spun them around to get that pinion angle down. Now... it's hard to say if it's correct or not. The pinion looks to be pointing down a tad more than it should, but the vibes are gone at 50 and 55 on the first test drive. But, there is either a vibe, or the bad axle/end bearing is causing some odd vibe around 20 to 25 mph. I may spin the driveshaft 180 degrees to see if that helps, but it's a solid shaft with the slip joint in the transfer case, so the phasing is good.

I'm almost wondering if the pinion is pointing too far down at slow speeds, and then tilts up enough with the drag at higher speeds... I don't have a camera I'm willing to throw down there though.

Then again, I was reminding my wife this evening that the driveshaft vibes have been there since we installed those leaf springs (how many) years ago. The vibe has only showed up since I replaced the transmission mount. So how bad can it really be...?

Clay
 
what does the pinion angle measure now? I would guess that it would be pretty close without the shim.
 
My rough country springs came with shims in the rear spring packs and caused driveline vibes from about 45 to 65mph. The angle miss match was equal to the shims so I took them out and everything was good, well minus the ride.
 
I'll have to re-measure the angles today, we used a protractor that wasn't marked very well yesterday. But, removing the shims now make the pinion within 1 degree of the transfer case. That we could tell... as long as we measured right. But, like I said, I'll measure again today.

So here's the results of the 3 different setups:

Shim angling pinion up: Pinion was close to driveshaft angle. Vibration/grumble at 50 mph, and got worse at 55.

Shim angling pinion down: Pinion was too far down. Vibration/wiggle at 20 mph, but seemed smooth at 50 mph.

No shim: Pinion seems to be close to transfer case angle, possibly within 1 degree. Vibration exists again a little over 50 mph, and still getting worse at 55 mph.

My transmission buddy looked at the angles and figured they look closer than when the truck left the factory, which sounds promising, but the vibe is still there. He's going to call his friend who works at a driveshaft shop, and see what he thinks; we are both leaning more toward an out of balance shaft. However... I still think there is a possibility that I'm just not close enough on the pinion angle. At this point it almost seems easier to get a few different angled shims & try them out; it only takes about an hour and a half to change...

Clay
 
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