random vibration/harmonic

[djw88]

my 2014 sierra slt has developed a seemingly random vibration/harmonic it happens at any speed and I can get it to go away if i change speed and/or turn.

i thought it was coming from the right front but now I'm questioning that. i jacked that wheel off the ground, spun it, and grabbed it to see if there was any play. it all seems fine.

what are your thoughts? it doesnt seem like a wheel out of balance or a wheel bearing to me but I've been surprised before.

 

98k miles. i feel the vibration in the floor, new struts two years ago, new tires one year ago maybe 6k on them oe size HT 18s. crew cab 

happens at any speed (in town or on highway)

Edited March 8, 2021 by djw88

[rav3]

At good start would be to post the mileage on your truck & miles on the tires. What brand tires? Any work been done on front end? Can you feel vibration in the steering wheel or in you butt? At what speeds? What model truck? Standard cab? Double door? Or crew cab? Are you running standard OEM size tires or the oversize 33's? This would help others to help you.

[djw88]

19 minutes ago, rav3 said:

At good start would be to post the mileage on your truck & miles on the tires. What brand tires? Any work been done on front end? Can you feel vibration in the steering wheel or in you butt? At what speeds? What model truck? Standard cab? Double door? Or crew cab? Are you running standard OEM size tires or the oversize 33's? This would help others to help you.

98k miles. i feel the vibration in the floor, new struts two years ago, new tires one year ago maybe 6k on them oe size 18s. crew cab

hope some of that may help

Edited March 8, 2021 by djw88

[djw88]

i havent checked u joints. ill check that next.

[Lsgun1]

I've driven a customers Jeep that the front driveshaft u joint was so frozen up the whole thing shook like crazy. Make sure to actually take down the shafts to check, not just for looseness.

[djw88]

It seems to be related to the V4 mode

[Grumpy Bear]

2 hours ago, djw88 said:

It seems to be related to the V4 mode

Does it happen at one rpm or multiples of some rpm? 

[djw88]

1 minute ago, Grumpy Bear said:

Does it happen at one rpm or multiples of some rpm? 

Seems like one rpm in V4 mode bit over 1000rpm maybe 1200

[Grumpy Bear]

Just now, djw88 said:

Seems like one rpm in V4 mode bit over 1000rpm maybe 1200

Would that be right around 40 mph in high gear?

 

[djw88]

1 minute ago, Grumpy Bear said:

Would that be right around 40 mph in high gear?

 

It will do it around 40. I can get it to happen at different mph seems like it happens when it's on the edge of jumping back into V8 mode.

[Grumpy Bear]

Okay....it's fine. The system is load based (AFM) but also has some other parameters it considers that will allow it to 'hold on' a bit to long sometimes to the V4 mode. ANY pressure on the pedal will force it to go back to full cylinder mode. I noticed this maybe a year ago on a stretch of highway coming into a small town where the speed limit changes from 55 to 40. Right at that 40 mph marker starts an ever so slight rise of road. I tap the cruse control up 1 mph just as I hit this spot and it goes seamlessly to V6. If the converter changes lockup status at the same time, and it will try, it will give a light shudder you can feel in the floor but otherwise goes unnoticed. 

 

It will do it at other odd points of load too or like when in V4 on the Interstate and get passed by a Semi. The bow wave my truck runs into will set it off. Same thing. Anytime it is over 1200-1500 rpm it just doesn't do it. 

[Grumpy Bear]

Here's something else. As you rack up miles the 'load' required to hold any speed changes as parts wear. Normally taking less load. Fractional sometimes but these tables are specific. It is a learning ECM but like a child it fumbles a bit until it learns. Every once in awhile we do something different in our driving that gets in that normal modes way. These things will drive a tech crazy trying to find. He just won't drive it like you do. Tech is good but finicky. 

[djw88]

well i hooked up a range disabler and it is better but it still vibrates in V8 mode around 1200-1500 rpm but not as bad as when it was in V4 mode.

any ideas?

[djw88]

any ideas? transmission? transfer case?

i may just take it to a shop im at a loss so far.

Edited March 22, 2021 by djw88

[djw88]

i took it to the dealer because i still have a year of warranty left on it. its bee there for 5 hours with no word back yet.