Update to my "chevy shake" 6/30/17 (got it back)

eboggs · June 30, 2017

Speeding ticket?

Jim

Nope ;)

Dezrado · July 1, 2017

Is the driveshaft on 0?

eboggs · July 1, 2017

Is the driveshaft on 0?

Please elaborate, I don't understand what you mean.

Dezrado · July 1, 2017

Please elaborate, I don't understand what you mean.

ive heard some driveshafts arent balanced correctly

Dezrado · July 1, 2017

There are five types of drive shaft induced vibrations that are associated with the installation parameters of a drive shaft. Were going to explain all of them in the hope that you can head-off a problem before it occurs. They are:

Transverse vibrations

Torsional vibrations

Inertial excitation vibrations

Secondary couple vibrations, and

Critical speed vibrations

Transverse Vibrations

Are caused by imbalance.

All drive shafts should be balanced at their application speeds.

Think about thiswhen was the last time you DID NOT have your tires balanced?

Drive shafts are heavymuch heavier than a tire

Drive shafts rotate much faster than a tire.

Common sense says that we should not hesitate to balance an object that is heavier and rotates faster than our tiresespecially if there is a possibility that it can lead to a serious failure.

All drive shafts should be inspected for missing balance weights at every service interval.

A transverse vibration ALWAYS occurs at drive shaft speed, and occurs at once per revolution. If you experience a vibration that is speed sensitive, have your drive shaft balance checked at your closest Machine Service, Inc location.

Torsional vibrations

Are caused by two things:

The U-joint operating angle at the drive end of the drive shaft, and

The orientation (phasing) of the yokes at each end of the drive shaft

A torsional vibration is a twice per revolution vibration.

A torsional vibration will cause the drive shaft, downstream of the front U-joint, to speed up and slow down twice per revolution.

That means that a power supply producing a constant speed of 3,000 RPM can actually be attached to a drive shaft that is changing speed 6,000 times per minute.

The amount of that change in speed, called the magnitude, or size of the change, is proportional to the size of the angle at the drive end of the drive shaft, or the amount of misalignment between the yokes at the drive and driven end of your drive shaft.

Torsional vibrations are SERIOUS vibrations

Why? Because when you vary the speed of a drive shaft, you not only vary the torque on all of its components, but you vary the torque on all of the components that are connected to the drive shaft Torque is LOAD.

When you vary the load, at twice per revolution, you start to bend components.

You know what happens thenthe same thing that happens when you bend a can lid back and forth. IT BREAKS.

Heres another way to explain it

Picture a drive shaft running at a constant speed and driving a truck or a large roller in a mill.

The front end of the drive shaft is connected to the power source and the torque coming out of the power source is fairly constant.

The rear end of the drive shaft is connected to the trucks axle or to the roller and it sees varying loads based on terrain or on how much work it is doing.

As the front end produces the load, the back end passes it on into the vehicle or stationary application and if all is well, that load is relatively constant and well within the torque carrying capabilities of your drive shaft

When something happens to alter the operating angle at the front U-joint of the drive shaft a twice per revolution change in speed is introduced into the application.

The front of the drive shaft keeps going constant, but the back end of the drive shaft starts to see the twice per revolution change in speed, and is always playing catch-up with the front.

This causes a twice per revolution twist in the drive shaft

A twice per revolution bending moment is introduced into the drive shaft welds, slip splines, U-joints and into all of the connected components in the application.

You, in effect, run a torsional fatigue test on the drive shaft and everything used to attach it to your application.

Drive shaft manufacturers run fatigue tests on the components and welds in their drive shafts by doing the same thing in their test labs. They hold one end of the drive shaft stationary and hook the other end to a rotary actuator. Then they twist it until it fails.

If you have a torsional vibration problem you will experience drive shaft tube welds that break, splines that wear prematurely and nuts and bolts that start loosening.

You will also start to experience vibrations.

If you see a failure that looks like this, you should suspect a torsional vibration problem.

When a drive shaft is assembled, its inner components usually consist of a slip yoke on one end and a tube yoke on the other end, and they are usually assembled in relation to each other. This is called PHASING.

Most drive shafts are assembled with their yokes in line, or IN PHASE.

Phasing affects torsional vibrations

A drive shaft that is in phase and has the correct operating angles at the drive end of the shaft does not create a torsional vibration.

Drive shafts that are NOT in phase will vibrate with the same twice per revolution vibration as a drive shaft with incorrect operating angles.

The easiest way to make sure your drive shaft is in its correct phase is to mark the tube and slip yoke every time you take it apart so you can put it back in its original orientation when you re-assemble it.Re-assembling a drive shaft out of phase is the #1 cause of torsional vibration that all-of-a-sudden appears in your application. If you suspect that your drive shaft is not in phase, take it to the closest Machine Service location for inspection.

How do you make sure your drive shaft application will not create a torsional vibration?

Make sure the operating angle at the front of your drive shaft and the operating angle at the rear of your drive shaft are less than three degrees and are equal within one degree. Make sure these angles are correct. Rotate the pinion if the problem is in a vehicle. Shim the driving end or the driven end if the application is a stationary application. Correcting torsional vibration problems is not rocket science. Fix the angles and you will fix the problem, its that simple.

To make sure the torsional vibration does not enter your drive system, make the angles at each end of the drive shaft equal with each other to cancel out the torsional vibration. However, the vibration will still be there if the angles are too largeso do whatever necessary to make the operation angles small.

Make sure your drive shaft is in phase the same phase as it was in when it was manufactured. Do not disassemble your drive shaft slip assembly unless it is absolutely necessary.

If you have a multi piece drive shaft set-up, make sure the operating angle at the front of each of your coupling shaft(s) (the shaft(s) with the bearing(s) or pillow block(s) on it (them)) are less than one and one-half degrees. Also make sure the operating angles on the rear drive shaft (usually the drive shaft with slip in it) are less than three degrees and are equal within one degree.

Inertial excitation vibrations

Inertial vibrations are also caused by the operating angle at the drive end of your drive shaft.

Inertial vibrations are created when you start changing the speed of a HEAVY drive shaft.

Inertial vibrations also create bending on drive shaft attaching components.

There is only ONE WAY to control an inertial vibration ALWAYS make sure the operating angle at the drive end of your drive shaft is less than THREE degrees.

A large angle even if it is an equal angle will still cause inertia problems.

Secondary couple vibrations

Secondary couple vibrations are also caused by the operating angle at the drive end of your drive shaft.

Every U-joint that operates at an angle creates a secondary couple load that traverses down the centerline of the drive shaft.

Critical speed vibrations

Critical speed occurs when a drive shaft rotates too fast for its length.

It is a function of its rotating speed and mass and it is the RPM where a drive shaft starts to bend off of its normal rotating centerline.

As a drive shaft bends, it does two things:

It gets shorter. If it gets short enough, it can pull out of its slip and drop to the floor or ground.

It starts to whip up and down or back and forth like a jump rope. If it whips far enough, it will fracture in the middle of the tube.

CAUTION: If you ever see a drive shaft with a bent, fractured tube, do not replace it with a new drive shaft of the same construction. It may fail again. Contact Machine Service engineering immediately.

EVERY drive shaft, no matter what its length and mass, has a critical speed.

The shorter the drive shaft, the higher its critical speed.

Converselythe longer a drive shaft, the lower its critical speed.

REMEMBER THIS: When a drive shaft runs at its critical speed, IT ALWAYS FAILS, and the failure is ALWAYS CATASTROPHIC.

Machine Service engineers will ALWAYS calculate the critical speed of any drive shaft they manufacture.

Machine Service engineers will ALWAYS make sure that drive shafts installed or specd by Machine Service will NEVER fail due to critical speed.

If you are in the business of repairing or altering drive shafts, NEVER lengthen ANY drive shaft, in ANY application, without contacting the engineering department at Machine Service.

eboggs · July 2, 2017

Well I think I'm going to attempt to take it back this week sometime. Still more vibration than I find acceptable in such an expensive vehicle. However, it is now only in the steering wheel. I know it to be abnormal due to the loaner I had for a week NOT having the same issue.

My concern is when I got it back they told me about the slight vibration being only present in the steering wheel, however they found it acceptable. I drove approximately 100 miles today (50 to and from) a Reds game, so 99% highway. The steering wheel vibration was apparent the majority of the trip, varying degree of intensity. Very few instances where it wasn't apparent at all....I'm at a loss.

eboggs · July 5, 2017

Taking it back tomorrow 7/5/17 due to steering wheel vibration. Have been driving it for a week and it is still vibrating, severity varies it seems with no rhyme or rhythm.

Dezrado · July 5, 2017

Hopefully they get it right this time

eboggs · July 6, 2017

7/6/17.....dropped the truck off this morning due to vibrations still present, mostly in steering wheel. Stated they did another pick test, sent the results to GM and were told everything was "in spec" and not to replace anything.

Surprised it took them this long to give me the shaft.

SlvrSierra · July 7, 2017

Is this a 6spd or 8spd truck?

eboggs · July 7, 2017

8 speed

FH212 · July 7, 2017

Yikes that sucks! And is disturbing to be honest......I just got a 2017 and so far so good thank god.

Jason001 · October 5, 2020

Im having the same issue in my 2015 Silverado 1500 LT... vibrates between 70 -80. I have to puy my hoodie underneath the console because the change i have in cup holdet about jumps out of it! I had road force tire balance done. Did NOT fix anything. Im at a loss for words.... next trip.is to Carmax where i bought it 8 months ago. I have bad experiences with them but what do I do? I have the Maxcare coverage that cost me $2500... ive heard most have to have the drive shaft changed to a steel one. Had anyone heard about this? Any suggestions???

Jason

lucas287 · October 9, 2020

@eboggs I want you to consider the possibility that what you're experiencing, and likely many others, is primarily a resonation issue. I'm not sure if it's a frame issue or exhaust issue, but I'm almost certain it's resonance. I have this problem too, where my truck seemingly has a mind of it's own. I've chased my tail on a few things and I've finally arrived at resonance, and am convinced that's it's a big contributor.

First and foremost, properly ROUND tires are very important. When I bought my truck it had some Michelin Defenders on it. I thought: sweet! Those are good tires! Yeah, wrong. 3 different Discount Tire locations and the lowest numbers I can get on 2 of them are low teens (13,14) and the other two are upper teens, low twenties. On many other vehicles, when I buy new tires, I am very upfront with Discount that they ALL need to be under or close to 10 lbs. of road force or else they are replacing tires until we get there. In fact, on my wife's 2018 Mazda CX-9, I just went through 8 Michelin Premier LTX tires before trying Falken Ziex CT60 and finally getting them all under 10 lbs. Smoothest that SUV has ever been.

So, tires matter a lot. But, tires are predictable and repeatable! They will vibrate at the same speeds EVERY time. If yours comes and goes, that's probably not tires. For example, the tires on my truck suck, we've established that. I do a burnout probably once a week on purpose just to round them out a little and try to shave the high spots down. It works lol, don't laugh. But I know they aren't perfect. Sometimes my truck feels blissful at 70 MPH, other times, eh, not so much. I'm hard pressed to believe that my tires are the only culprit.

I've spent countless hours modifying the TCC lockup strategy, ramp tables, pressures, etc.. all with no success in the vibrations actually getting better. Had the 8 speed TSB done where they flush out the old fluid and it helped a little, I guess, but nothing dramatic. I've run E85 (tuned for it) and every alcohol combination in between. I've adjusted my pinion angle to cancel out my transfer case angle. I've installed traction bars to prevent axle wrap (which causes vibrations). All of this helped to some extent but I was never satisfied until,...

About a month ago I was doing some tuning with HPTuners and I was parked, revving the engine. I had my hand on the steering wheel and as I came up to 1,500 RPM I started to feel a vibration that intensified at 1700 RPM and then diminished by 2000 RPM. I did this several times and it felt the same. Every. Single. Time. I went for a drive and started to pay attention to the tach and where I feel vibes. With every gear as I swept through that RPM range, yep, vibrations! And where is my tach at 70 MPH? 1600 RPM! 80 MPH? 1800 RPM! My steering wheel, console, and floorboard all have the same vibrations at those speeds/rpms as it does in park just revving the engine. I could be driving 70 MPH feeling vibrations in 8th gear, drop it to 7th and voila vibrations gone at 2100 RPM..... hmmm

There's actually a thread about it on here that I started to study:

I immediately realized that many other people experience this SAME phenomenon. I started doing research on helmholtz resonators (j pipes, 1/4 wave resonators, side branch resonators) and how they function. So, I figured what the hell, why not try it?

I had a muffler shop weld in a 2.5" piece of pipe into the section just after the muffler as it turns up to go over the axle. I might it adjustable from 31" to 48". I'm still playing with it the optimal length, but it genuinely feels like it helped. 100% gone? No, definitely not. But it's smoother for sure. It's smoother going through the gears in that RPM range and I can now use 8th gear. I still feel some vibes, but, remember my tires suck!

Next step is taking the approach that Lexus used to quell vibrations on the RX350:

https://www.clublexus.com/forums/rx-4th-gen-2016-present/807592-2016-rx-350-excessive-noise-and-vibration-74.html

Turns out that Ford, Dodge, Chrysler, all have used similar strategies to cancel resonance (vibrations) for decades! Ford installs exhaust dampers on their dual exhaust equipped ecoboost Raptor trucks. They even used them back in the 90s when they did dual exit pipes in the front of the tire.

Heck, look at Ram trucks. Since 2009 they've used frame mass dampers to cancel out certain unwanted vibrations:

https://www.ramforumz.com/threads/vibration-in-gas-pedal.247181/

Take it for what it's worth. It's my next step and I think it'll be the nail in the coffin.

lucas287 · October 9, 2020

...another supporting argument is that exhaust resonance changes dramatically with EGT (exhaust gas temperature). You see it's a complex calculation regarding EGT, its influence on exhaust velocity, or speed, and RPM. That's why it changes so much day to day! It's why a cool morning feels different than a hot afternoon drive back home.