Hi all, new member, joined just so I could pass on what solved my vibration issue, after reading so many posts while trying to solve mine.

History: 06 4.7 QC 1/2T
installed LSD and 4.56 gears roughly 120Kmi mark. Picked up a vibration at 84mph. Lived with it for over 80Kmi, until LSD broke. then shop misinstalled and result was destroyed gears. Took to another very reputable shop. they could not install new gears without major noise. I finally had them put factory 3.92 back in just to stop the nightmare. I read up and learned how to install new gear set myself. Replaced all bearing and races along with a new Yukon 4.56 gear set. All good except the vibration was back at 82-84 mph and gone by low 90s. The stock gears did not do this. Now two sets of 4.56 have shown same vibration. So I took DS in to be balanced. WRONG! do the math and figure out what RPM the DS is spinning at vibrat9ng speed before contacting shop that cannot spin the shaft that fast. They took the factory runout of the shaft and split the difference by slightly bending it. They said it balanced great....at 2000rpm. The vibration is occurring at 3800+RPM. I got dynotech to make me a new 5" aluminum driveshaft that they wouldbalance up to 5000rpm. They said critical speed for that length and diameter of shaft was around 6300rpm. While shaft was being made, I borrowed a known good trucks DS and swapped. Vibration still there. All I was doing by buying dynotechs DS was undoing the destruction the local balancer company had done. See a pattern here?

When DS was installed, vibration the same as expected. Replaced tailshaft bushing in tranny - no change. So now I have new gears, bearings, slip yoke, u joints and high performance DS and still have vibration at same speed. I even went so far as to have a buddy make a spacer that boted between the u joint yoke and the pinion flange to take up 1.25" of slip yoke in the tail of the tranny, just to rule out yoke wobble. It was no better. This vibration was easily replicated on drivestands with the cruise set at 85mph. Checked axles, bearing, removed wheels, rotors, etc and vibs still there.

Finally, I just happen to look at the nose of the diff while the truck was on stands, in gear, at idle as opposed to the many many times I watched it at 85mph. I could see the pinion flange was wobbling slightly. I measured it at 10-11 thou at the edges of the flange. I got a new one from the dealer and checked it at 6-7 thou. I checked it at the raised lip that inserts into the yoke and it measures 5-6 thousanths runout, as opposed to disk wobble measured at the 90 degree edges of the flange. This appears to be acceptable from most literature. I marked the high spot on the pinion shaft and the flange and re clocked the flange 180 degrees (I have spacer, not crush sleeve). The runnout precisely followed the shaft, not the flange, meaning the pinion shaft is not straight (or possibly pinion bearing). Keep in mind this is the second set of gears, first was motive, to display this.

I shimmed the pinion yoke to flange with .004" (two stacked) copper washers to offset the flange wobble. The line between two mounting bolts was exactly 90 degrees out to the flange high spot. You can't even see the space when installed, its so minor. VIBRATION GONE. I couldn't believe such a minor change could solve the whole back end of the truck shaking at high frequency at 84mph.

Here is my theory: when we put 4.56 gears in these trucks, the following is against us. 1) the DS is 6 feet long. Nearly no truck still use a long one piece DS anymore. 2) we spin it much faster, due to the tall wheels. So my theory is that this application is especially sensitive to runnout at either end of the DS due to it's length and high rpm. Since most manuals say to keep pinion runout <.010", gear makers are probably thinking their QC test limits are effective.

I really think the best way to solve this is to get ahold of a system driveline balancing rig and balance the whole back end of the drive line in place. Here is a link:

http://www.vibratesoftware.com/html_...ce_Feature.htm

I see them on Ebay, but as an EE, I am inclined to take a scope home along with a piezo buzzer and a timing light and see if I can't accomplish it the one time I need to without much investment, and learn a bit at the same time. The kind of balance I am looking for is very simple.

Hope this helps someone. I read so many threads over months of this issue and very few people solved their issue. The ones that did had a bad u joint, or un balanced shaft, etc. Most could not be solved and it seems the symptoms are too similar. I think in hindsight, getting ahold of a EVA and putting the transducer on the botton on the pinion housing would have exposed this from the start, and solved it at the same time...

I would be willing to bet dodge truck factory pinion shaft specs are tighter than aftermarket for this very reason.

 

.............. I've seen tons of people on here with 4.56 gears without the problem you are describing....

I'm more inclined to believe that there is something else wrong... You changed both gears the rear end and in the transfer case right....? (unless you're a 4x2 then disregard my comment)

I couldn't even begin to diagnose the problem without seeing it in person though...

Where are you driving 84-90 MPH anyways...? They have speed limits like that in Texas....?

 

Try a google search on dodge 4.56 vibrations and you will find tons of people describing the same issue...not saying many, many are not successful, but there is a tolerance spread you know..

as for the speed limit...you drive your speed, I'll drive mine :-)

Yes, its a 4x2. No, its not a tire or wheel issue, the frequency is wrong, besides the fact it has transcended tire changes and balances. It is unaffected by what gear the transmission is in, so it is definitely from the output of the tranny, back. The frequency versus road speed really narrows the problem down, which I did a long time ago. I just never realized how a small amount of unbalanced runnout at the end of a long high speed shaft can affect smoothness.

The DS manufacturer balances the slip yoke, and both u-joints, but does not include the pinion yoke (or of course the flange) in their setup. Besides the pinion itself, that's all thats left rotating at that rpm, hence frequency.

 

Good find and explination of the fix..

 

well we all know that the Power Wagon had the 4.56 gears from the factory so I just went through and compared stats and part numbers....

The Power Wagon has a completely different rear differential and a few other components that I will let the OP figure out on his own, and I am also betting that it has differences to nearly all of the driveline angles. Also a good reason why Dodge Engineers put a 100mph speed limiter on the power wagon, my guess is they didn't want to get rid of the "vibration" at high speeds.

If it was a "frequency" issue you would be suffering from nearly uncontrollable vibrations and it would resonate itself to pieces eventually.

If you have found (and I assume read) all those other threads elsewhere... go find your own solution or quit being a smart ***. We haven't seen your truck nor have we driven it, so excuse us for going through and starting at the common things first.

Most vehicles that come stock with 4.56 gears are made for towing and off-roading where Torque is required not high end speed/power.

Think about it this way; you've dramatically increased the rotational speed of all of your drivetrain components and you expect to have zero problems changing something that was engineered the way it was (stock) by people that have far greater automotive, mechanical, and design knowledge and experience, as well as access to test equipment that far surpasses anything most people can conceive let alone get to even see operate.

There is a reason Dodge's Engineers and Designers didn't offer a 4.56 gear package on the 1500, and only allowed you to pick from 3 (now 4) axle ratios 3.21, 3.55, 3.92, and 4.10. Then in the 2500 & 3500's they only offer 3 Axle Ratios on all the models EXCEPT the Power Wagon, which has a completely different drive train (except for the transmission), which are 3.42, 3.73, 4.10... whereas the Power Wagon has the one and only 4.56 in the entire model line-up, with completely different drivetrain components.

There is a reason for all of that, so I have a few suggestions:

1) Sell your Hopped Up Truck and purchase a Power Wagon with OEM 4.56 gears

2) Buy each and every single drivetrain component from a Power Wagon and Put it on your truck

3) Change to a 4.10 and hopefully you'll get rid of the vibration all together.

4) Put the Stock Gears back in

5) Continue to try and make what you have work, and spend excessive amounts of $ in the process.

6) Live with what you've got.

Those are the options I'd choose from personally, and if you have a problem with them, well in all honesty... too bad... you posted on this forum asking for advice and/or help so that is my contribution.

I am 100% positive that no amount of balancing and adjusting what you have now will correct those issues.

 

Didn't realize the powerwagon had a limiter at 100mph but makes sense. My driveshaft is spinning near 30% faster than my orginal 3.55's and it still doesn't vibrate mind you I've only driven to maybe 90-95mph to pass someone. At that point you really start to hear the drivetrain turning quite a bit but that's like my driving 115-120mph with the stock gears. I would never expect a 5000#+ truck to be designed for this or worry about tweaking it to run at 100mph. If I want to drive that fast I'll just take my car.

 

...see below

 

Look, I have no beef with you friend. If we got off on the wrong foot for anything I did, I apologize. Like I said, I only joined to share something that I solved that I have seen plague many others. How can I be a smart *** doing that? Go back and read your first reply. You picked me apart for claiming to have a solution, picked me apart for driving over the speed limit, etc..then said the problem could be any number of things (other than what solved it for me), too many to guess.

Have a better day :-)

 

I am confident that this balancing system will not work for everyone, there may be many more things at play than simple balance issues as every vehicle is different. There are other factors of the suspension geometry that can adversely affect the drivetrain. This is why Dodge pays big bucks (in the order of millions of dollars per year) for engineers and equipment to figure this stuff out.

I didn't need to be part of the solution, frankly it doesn't phase me in the slightest that I wasn't. And I am sure that you will help a few people in that regard.

I retract the statement regarding "frequency" as many people that use the word frequency and vibration end up referring to resonance, so I assumed that is what you were referring to.

I guess I did misunderstand your first post, and for that I apologize. I was under the impression that you were still experiencing the vibration as I didn't see the copper washer part of your Original Post upon first read-through.

I personally might have chosen to use a different material than Copper as it might corrode over-time and may fail suddenly, but cheap enough to put a new one back in I suppose, it is just the time investment at that point.

Now correct me if I am wrong, but most shops that change gears on trucks usually measure the yoke angle and make sure it is well within specifications no? (I called my transmission shop mechanic, and he said that's usually the first place they check after wheels after a gear change.) From personal experience with an old hot rod 1/2 ton, it is usually the pinion angle that needs to be adjusted, as under load the transmission and engine move slightly, which can change that pinion angle by as much as 2 degrees, which can cause all kinds of problems.

My Last note: With the copper washer paragraph this thread is useful and informative, got distracted by the title of the thread and the whole background story. My fault there.

 

........