Shake or Vibration Issues

[abominable z71]

I believe the axles are machined by automatic milling machines, so what is the probability that the lug nut stud hole circle could be machined off center? I suppose it is possible if there was a glitch in the machine programming or some problem with the machine hardware itself. And even if, what is the maximum permissible tolerance on such machining? Is quality control sufficient to catch such issues before they produce thousands of parts with this defect and sell them to GM? Would GM knowingly install defective parts on new trucks?

I can assure you my left rear axle bolt circle is completely off center by .015" and the right rear is within .005" variation from center to each of the 6 studs. Typical machining prints will hold a 3 decimal call out at .010" and a 2 decimal call out at .030". Where I used to work assemblies we designed and dimensioned with 4 place dimensions were held at .0005". It's not a hard fast rule but pretty typical of most drawing standards.

[pm26]

I can assure you my left rear axle bolt circle is completely off center by .015" and the right rear is within .005" variation from center to each of the 6 studs. Typical machining prints will hold a 3 decimal call out at .010" and a 2 decimal call out at .030". Where I used to work assemblies we designed and dimensioned with 4 place dimensions were held at .0005". It's not a hard fast rule but pretty typical of most drawing standards.

Do you suspect sloppy tolerances in general or some flaw in the machining process? Maybe they lost something when they transitioned to metric system?

Edited December 17, 2015 by pm26

[hotrodz37]

Rides much better IMHO. It tightened things up a bit and improved the handling. As I mentioned before the truck would vibrate pretty bad when really getting on the gas 4300 RPM plus. This helped in this area significantly, I'm thinking about getting another set and clamping in front of the axle as well to see if it helps. I'm also looking at fabricating my own body lift blocks out of polyurethane to replace the hard plastic pucks that came with the body lift to gain a little damping.

 

Attached are the pics. I mounted them 7" from the edge of the lift block to the center of the clamp I don't think this measurement is crucial. I am curious to see if moving them further away from the block would be better. That's more of a weekend testing thing though maybe this weekend ill try and find the best distance and if front and rear clamps are better or not. I'll try and dial in the best setup and let everyone know.

 

 

Greatly appreciate you experimenting for the rest of us! I see you mentioned it helped it over 4300 rpms which would help reduce axle wrap, but did it help with the highway vibes at all, that's what I'm chasing. Thanks!

Edited December 17, 2015 by hotrodz37

[abominable z71]

 

Greatly appreciate you experimenting for the rest of us! I see you mentioned it helped it over 4300 rpms which would help reduce axle wrap, but did it help with the highway vibes at all, that's what I'm chasing. Thanks!

Yes it did. Going to experiment some more this weekend and see how much I can reduce them. I've only got up to speed twice since putting them on but they feel significantly reduced thus far.

[abominable z71]

Do you suspect sloppy tolerances in general or some flaw in the machining process? Maybe they lost something when they transitioned to metric system?

Not sure , depends on the manufacturing process. I would expect the hubs to be done in multiple operations probably turned then, hardened, then broached then bored then a final turning all done on different machines and it looks like the boring op for the stud holes was off center.

[rshad]

Maybe we need someone to get a set of aftermarket complete axles put in and see what happens.

[WLC]

Where were the axles made? One might guess? Haven't seen GM chime in lately on the thread at least to try to help! Someone knows(said this before) at GM or at one of the factories where these bad parts were made. I admire the hard work by many on this thread to solve this vib issue! There will be hero's if not already for their effort to solve this problem!! Let's dry up this thread. Sorry for those with vibs in their trucks.WLC

[kcgmcblk]

 

I am in the process of the BBB lemon law and have a tentative arbitration date of week after Christmas or the first week of Jan. Just a few days ago the vibration was bad and very obvious. The last 2 days it is almost gone. Hard to explain why as I am driving on the exact same roads and same speeds. The difference is road and outside temperatures. It has been near freezing here last couple days where it was 65 deg when I had bad vibration. My concern is that it won't vibrate when I take the arbitrator for test drive. Any ideas or explanations??

 

It's been a very long and drawn out process to get to arbitration and now conditions have changed. I really don't think these trucks fix themselves! After 20 tires, 16 wheels and 2 new shocks I'm as frustrated as can be!

Edited December 18, 2015 by kcgmcblk

[pm26]

Where were the axles made? One might guess? Haven't seen GM chime in lately on the thread at least to try to help! Someone knows(said this before) at GM or at one of the factories where these bad parts were made. I admire the hard work by many on this thread to solve this vib issue! There will be hero's if not already for their effort to solve this problem!! Let's dry up this thread. Sorry for those with vibs in their trucks.WLC

I am not sure but something tells me that it was not in Switzerland or Germany. Perhaps Zimbabwe?

Edited December 18, 2015 by pm26

[C6Bill]

Hey Bill, have you had time to see what kind of fuel mileage your getting. Just curious if they have found 1 or 2 more mpgs yet. At least fuel prices have dropped so not as big of deal.

 

 

Just an FYI, I took a nice trip yesterday 75 miles up to NH averaging 60 to 70 MPH I got 18.9 MPG. On the way home I took 495 so it was 95 miles with speeds between 70 and 85 MPH, I averaged 17.5 MPG for that part. Overall I'm fine with those number. And a total of 0 vibrations ;)

[Wrench589]

Ah yeah, good call. Here is the link to the body lift. http://zoneoffroad.com/zone-offroad-products-15in-body-lift-chevy-gmc-pickup/c9151

 

Maybe the spacers keep enough of the cab off of the frame that the vibes don't make it into the driver area.

 

Here's a thought. The new SUVs use new "shear type" body mounts. I think the pickups to also. I did some research and what that means is the mount is flexible in the vertical direction, but very stiff /locked in the horizontal direction. Why did GM go to these? To improve the ride! Haha. But, I believe the intent was to reduce the horizontal body jiggle that "body on frame" vehicles exhibit in and attempt to make the vehicle have a firmer road feel, like the unibody competitors. Of course, it is certainly possible that this style of body mount is the transmission path between the drivetrain/road vibrations, and the cab. Because, these vibrations can excite the frame in both the vertical and the horizontal directions. But, the shear type mounts will likely only absorb/dampen in the vertical direction.

 

And that's why GM have tried to "equalize" the cab mounts on every vehicle at some point in time. And, to no avail. Why? This was an effective technique with older, traditional body mounts. Hence, GM is hoping it will help now. But, I suspect that the shear type simply are too stiff in the horizontal direction, regardless of any attempts to equalize. And, any/all vibration going into the frame that ends up in the horizontal direction, goes straight into the body.

 

So, if anyone is brave enough to replace all the shear-type mounts with older style might just see something interesting.

 

As for the lift kit, is it possible that the spacer could have provided some additional isolation in the horizontal direction and, if is slipped at all, could explain why the vibration came back. Bit of a stretch, but it is a theory.

[Wrench589]

Hub flange turns true. Bolt circle for the studs is completely off center shouldn't be an issue for hub centric wheels except the wheels are drilled for cone seat nuts which inevitably tries to center the studs in the holes, and since the center portion of the wheel is oversized by about .040" to allow a free fit on the hub pilot flange the wheel is allowed to be mounted with it's axis off center from the hub center and aligns itself with the bolt circle. I have one tire with a little bit of runout in the tire itself I'm going to try and mount the high spot of the tire 180 degrees out from the high spot on the stud bolt circle and see if that offers any improvement might alleviate the up and down during rotation but the center that the balance was used for will still be off by .015".

I measured the bore of my wheels (factory 22") and the hub pilot OD. Difference is about 0.002-0.003". Anything more than about 0.004" top and it is no long hub centric! So, if you have 0.040" clearance, it's not really hub centric.

 

Now, I have a fundamental problem with GM's design. It is totally illogical to have a hub centric design AND use tapered (cone) lug nuts. These lug nuts are the "cheap and dirty" design for lug centric.

 

Someone stated that all/most OEM wheels are hub centric. But, don't forget that is fairly recent direction in the industry. For those of you around in the 60's and 70's, most, if not all, domestic full size vehicle (including pickups) had good old steel wheels with lug centric design. The hub bore was very loose on the hub, and the tapered cone lug nuts centred the wheel. Simple, cheap and it worked. Now, some aftermarket wheels had a lug nut with a shank on it that typically went into the hole in the wheel which was oval shaped to accommodate a range of bolt circle. Those kinda sucked!

 

Fast forward to modern day. My F350 Superduty has hub centric wheels. And, they are a bitch to get off, because they are a tight fit. Need to be to run smooth (which they do!). But, the lug nuts have a built in flat washer where they engage the wheel. So unlike the GM design the lug nuts are not fighting the hub to centre the wheel.

 

Now, Abominable reported that the bolt circle is concentric to the hub pilot. I am interested how that was measured, because it is pretty difficult to measure accurately. But if it is out, the question is how much of a problem does that cause when the lug lugs are fighting the hub? Don't know. Certainly explains why aftermarket wheels that are lug centric still vibrate if in fact the bolt circle in not concentric to the axle running centre.

 

As for runout, I would think anything in the 0.005" on the hub and/or bolt circle should run pretty good.

 

OK, now about Foadforce Balancing. I think chasing the tires and Roadforce balance is not productive. For years, we didn't even bother to Roadforce balance tires and other than the odd belt separation, vibration issues were not that big a deal. In fact, I bet just about everyone on this thread owned a GM product recently that ran smooth as silk and was within the "old" spec of 25 lb. so why all of a sudden it is required to reduce the spec to 15 lb? And even that doesn't work? Because it's not a Roadforce problem! There is something else in the design that made these vehicle super sensitive to any and all vibration. And it is unreasonable and impossible to eliminate all the residual unbalance and/or runout in all the various rotating components. GM is wasted everyone's time chasing all that stuff. There is something fundamentally wrong with these vehicles and until that is addressed, all this is a waste of time.

 

Last comment. Someone made a reference to the SUVs and that there are essentially identical to the pick pips other that the "box" on the back. Not 100% true. the pickups have a leaf spring rear suspension while the SUVs use coil springs and control rods in the rear. So, that is fundamentally different. And, for what it's worth, the SUVs don't seem to have anywhere near the vibration severity that some of the pickups do. Unfortunately, the SUVs have the "buffeting" issue which is brutal!! Anyway, the difference in the rear suspension certainly supports the notion that the excessive vibration in the pickups may be related to the rear suspension.

Edited December 20, 2015 by Wrench589

[southern_sierra]

 

 

Just an FYI, I took a nice trip yesterday 75 miles up to NH averaging 60 to 70 MPH I got 18.9 MPG. On the way home I took 495 so it was 95 miles with speeds between 70 and 85 MPH, I averaged 17.5 MPG for that part. Overall I'm fine with those number. And a total of 0 vibrations ;)

Nothing wrong with that at all. They must have turned the fuel screw back just alittle. Thanks for the info

[4x4 350]

Hey I dont know if anyone else tried this but I tightened all my rear U bolts and it reduced my vibration. I had a 40-55 vib on the highway. The intensity was reduced and I only have a slight vibe around 55 mph now. It feels much better all around. I was able to get at least 6 turns on every nut. Im curious about the leaf sping clamps too, I might try that this weekend to see if i can eliminate the vibe or atleast close to it. When I have a load in the truck the vib is very close to not being noticeable.

Edited December 18, 2015 by 4x4 350

[BTZ7105]

I've got a vibration sound in 5th & 6th gear at 40-55mph low rpm, any thoughts on what it could be? The dealer has re shimmed the rear down to .008, installed new front diff, transfer case reprogram. Nothing they have done has helped, I actually think it's gotten worse.