Cyclic shake/bounce/vibration

[Gibbs]

Truck in signature with approx 8K miles, all suspension completely stock. At around 4500 miles, started to notice a cyclic shake anywhere between 45-70 MPH. Cyclic meaning that it will shake or bounce for 2-3 seconds, then stop for about 1 second, then repeat indefinitely while the conditions exist. It is not a constant vibration like I had in my '04.5 when the driveshaft was out of balance. Its as if you're driving over a series of rumble strips, then nothing, then rumble strips again. Its only in a smooth stretch of road that it happens, and only when i give it a little throttle, putting it under a slight load. You can see this shake in the transfer case lever and feel it in the seat and floorboard.

Truck has been to 2 different dealers. First dealer balanced tires on 2 different occasions with no change (OEM Firestone Transforce AT 275/70-18 on chrome clad steel wheels). They looked at the rear driveshaft and said no weights were missing. A tech friend informed me that he didn't have a good impression of their tire balancer, so I called Chrysler and got an appt with another local dealer. The other dealer said that it "felt like a 2500" when they test drove it, but the road in front of the dealer is pretty rough, so I'm not surprised. They rebalanced the tires and said they were all way off, and had to roadforce the rears (broke down and repositioned) in order to get an acceptable number. The cyclic shake was still there, but it narrowed down the occurance to between 55-70 MPH.

Since I've had the tuck, I've been on the lookout for a nice set of take-off Laramie wheels/tires. At around 7000 miles I bought and installed a set of takeoff Laramie Limited wheels and tires with less than 200 miles on them. They are cast aluminum 20s with OEM Firestone Transforce AT 285/60-20 tires. These were pretty much brand new and factory balanced. Not only do they look better to me, but also helped to eliminate the wheels/tires as the source of the problem. Having lower sidewalls does transmit more road bumps, but not that bad.
The shake is still there. A tech friend of mine at the original dealer has opened a STAR? case with Ram and I am waiting to hear back to see the next step.

I did take the driveshaft loose at the pinion and rotated it 180* and it made no difference, so I put back where it was.

Any ideas are welcomed, as this is super annoying on a brand new truck. And I want to clarify that this is nothing to do with the "ride", as this is my 3rd Cummins 2500 and I'm used to the bumps, etc. This is strictly a cyclic shaking problem that shouldn't be there.

 

[AEdelheit]

It sounds odd but dont overlook alignment, I have seen some of these trucks come with way too much toe in from the dealer and that can cause vibration issues. If the dealer said they aligned it but do not have a print out then they probably did not do it.

 

[Gibbs]

As far as I know they haven't looked at the alignment. I can check the toe fairly easily, though.

 

[AEdelheit]

As far as I know they haven't looked at the alignment. I can check the toe fairly easily, though.

True, I would go for almost 0 toe if you can!

 

[cerberusiam]

As far as I know they haven't looked at the alignment. I can check the toe fairly easily, though.

Not close enough to get it where it should be, if you can find an operator that knows how get it done on a machine.

With the 3.42's I would be looking at injector balance and operation in those low rpms. These trucks simply do not like the low rpms, the torsional harmonics do really weird things to noises and vibes. Injector balance becomes extremely critical that close to idle rpms.

 

[Gibbs]

Not close enough to get it where it should be, if you can find an operator that knows how get it done on a machine.

With the 3.42's I would be looking at injector balance and operation in those low rpms. These trucks simply do not like the low rpms, the torsional harmonics do really weird things to noises and vibes. Injector balance becomes extremely critical that close to idle rpms.

The tires don't seem to be wearing out prematurely on the outsides, so I'm not sure if the toe is that far out. I've never heard of alignment causing any sort of shaking/vibrations. Not saying it can't, just that I've never heard of it. May be worth checking.

The injector balance is interesting. . Is this something the dealer can check fairly easily? What would be the solution if they're out of spec? I know that at 55MPH I'm at roughly 1200 RPM, but at this speed I'm driving it with a light touch on the accelerator. Sometimes I'll manually downshift to keep from lugging it.

I did try shifting to neutral one time when I was going down hill at 70 MPH on a smooth stretch of I-75, and the cyclic shaking continued. I have not been able to reproduce this since switching the wheels/tires, because it requires a smooth road and a decent downhill so I don't lose speed.

I can downshift to 5th, which raises RPM to approx 1500 at 55MPH, and the shaking is still there.

Thanks for suggestions


EDIT:
Just went for a test drive and got it to do the shaking. Its pretty bad at 62-68 MPH. I can't seem to get it to happen at 70+. At approx 65 MPH, while it was shaking, I downshifted to 5th and got the RPM up to 1750-1850. It was shaking just as bad in 5th as it was in 6th. I drove it at this speed for a while. I coudn't get it to do it in neutral like it did on the interstate, as it really seems to do it while under a light load. But the road wasn't very smooth, either. I have to find a pristine road to try it out.

 

[Raymond Yost]

What did you find out on this? My 2011 has a vibration with the front driveshaft in around the same speeds. Pull the front driveshaft, and it’s gone.
Note: Front halfshaft u-joints we’re both just replaced

 

[nukegm]

comrade - might try running the truck while its on a lift. watch the wheels go round and round. also look at the driveshafts. bring it up to road speed. perhaps a bent axle...? hopefully the problem would be obvious when on the lift. i did this on an old 70 bronco with similar problem....30 years ago. good luck and cheers!

 

[Gibbs]

What did you find out on this? My 2011 has a vibration with the front driveshaft in around the same speeds. Pull the front driveshaft, and it’s gone.
Note: Front halfshaft u-joints we’re both just replaced

Sounds like you've narrowed it down. In your case it could be worn splines, worn CV ball or out of balance front driveshaft. Maybe a good driveline shop could check it out. You might could run it up on stands like @nukegm suggested and see if you can see any visible runout or wobbling.

I'm still waiting on my dealer to tell me when their area rep is coming by to look at my truck. In the meantime I installed the driveshaft 180* out at the pinion and the shaking did not change. I ran it up on jack stands to see if I could see anything, but I didn't run it up to speed yet. (I still need to do this) I let it turn whatever speed it naturally wanted to go in drive at idle speed.
I did see visible runout in the rear driveshaft, which measured out to .028 at pinion, .015 in middle, and .030 at transfer case end. According to my 2003 factory service manual, these are out of spec (they had steel driveshafts back then) If anything, I would think the 1 piece aluminum shaft in mine would be even tighter tolerance. But there's no way the runout would have changed from factory unless something got out of tolerance in u joint, etc. I'm trying to figure out something that may have changed since new that would start this vibration/shaking. ..
I looked closer and found a spot weld on the rear driveshaft all by itself. Actually 2 spot welds; one is deeper /burnt in more than the other. Either a weight came off or it was a mistake from the factory.

I also noticed a line of grease that has slung out of the u joint at transfer case. There's a grease trail on the exhaust, bottom of cab, and on DEF tank which I think is abnormal. I'm limiting my driving until they can check it out. 8000 miles this is ridiculous. I did put my stock wheels and tires back on so it's one less thing the dealer or area rep can blame.

 

[Gibbs]

I forgot to mention earlier...In searching for cyclic vibration, I did find a thread from 2012 where a guy had a similar problem. https://www.turbodieselregister.com/threads/help-cyclic-driveline-vibration.240186/#post-2320614

Member @sag2 responded with the following:
"Search on drive line vibration and you should find some of my posts detailing this drone/vibration. It is normally caused by the intersection of two vibrations, one being the 3rd order engine firing frequency (normal six cylinder engine firing pulses) in combination with a first order drive line vibration. You need to go back to what you did to break the truck. If it was never there and just appeared it is most likely caused by someone pulling a drive line and not replacing it in exactly the same position. If that isn't it, the motor mounts, exhaust hangers, u-joints, and drive line balance are most likely the source. Once you have it, it can be very difficult to isolate and correct. Replacing lots of parts is usually a waste of time and money."

This is what led me to look closer at the driveline. I'm hoping they'll replace the rear driveshaft assembly, as I believe it's out of spec. I'll update the thread when I find out something from FCA, if they ever get around to coming to the dealer.