DanaDenali

Vibration Log: 12/24/14 Preface: I apologize for my similar multiple posts under different threads but after reading all the different treads, this post seems to have the most information about both symptoms and possible fixes. It has been very helpful in assisting me toward documenting my vibration issues and to be able to hand over a detailed account to the service manager. Here’s where I stand: 2015 Sierra Denali 4x4, 5.3L, Crew Cab, (I do not have the Driver Alert Package), Short Box. 20” Factory Wheels, Nitrogen Filled Goodyears. 1 month old, 1400 miles. Felt vibration on 3rd day of ownership when I drove on the interstate for the first time. At 65 the vibrations started and as I accelerated thru 75mph, they worsened. I pushed to over 85mph, where the vibrations lessened. I adjusted my speed to find the spot where I had the worse vibration; it was at 77/78 mph. I called service department and asked them to look into the problem, I thought that this was a tire balance problem, what else should I have thought with a new vehicle after 3 days? Took my truck in, and they gave me a new SLT to drive. This was a nice truck that had NO vibration. I picked up my truck 2 days later and they told me they had road forced balanced my tires and I should be good to go. Unfortunately, for the next 2 weeks I drove on city surface streets and lower speed state highways. I never noticed any major vibration. First real road trip: Dec 23rd, 300 miles on 80% interstate with family. First leg was a mountainous 45 mile stretch of interstate with a lot of accelerating and braking, so noticing vibrations were the least of my worries. 2nd leg was on I-40 across almost the entire width of Arkansas, west to east. Once on I-40, I kicked it up to 80mph. Within minutes, the cab area was vibrating (shuddering side to side) enough to slosh iced-tea out of the cup sitting in the cup holder. Soon after that, the DC plug in the back of the console vibrated out of the socket. Everyone in the truck was feeling the vibrations. I backed my speed down to under 70mph and the vibrations lessened. I called my dealership from the road and told them the vibrations were still present, and maybe even worse. They made an appointment for me next Monday. For the next 2 hours I tried to stay around 70mph where the vibrations were present but not severe. Any time I had to accelerate to pass, the bad vibrations came back. The last hour of the drive, I hit newly paved interstate and used this stretch for an ad-hoc a vibration test. Vibrations were worse when: Accelerating thru 75mph up to 85mph Decelerating (coasting) from 80 to 74, vibrations seemed less. Sustained speed of 78mph was the nastiest We arrived at our destination and the first thing I did was to fire up my laptop and search for vibration issues on GM trucks. Yahtzee – here I am. Yesterday, I took drove my truck to an in-law who is a Ford mechanic and asked him to drive my new GMC and to give me some sort of assessment of my vibration issues. I gave him my keys and off we went - our only limitation was we were not near an interstate, so we were blazing up and down a state highway, and just when the major vibrations started, he had to back down on the accelerator, but we both definitely felt it. He did a couple of speed runs using the manual settings. In M5, at around 75mph, the vibrations “seemed” less than when in overdrive. After the test drive, he really couldn’t make a grounded assessment, but what did was give me some guidelines on logging the issue. He had me document the following on my trip back home: Time from cold start to fist feeling major vibration: 22 minutes Monitor Air Pressure on all 4 tires: cold start to vibration and thru end of journey. Look for one tire to pressure up faster than the others. START: LF 35, RF 35, LR 34, RR 35. Vibrations Start: RF went highest first to 37, others followed within minutes and all stayed at 37 throughout trip. Use the new 8 mile stretch of interstate to do the following: Find speed with worst vibration and accelerate and decelerate thru that point: 77 / 78 were worst. Accelerating thru 78 kept the vibrations going to about 82. Decelerating (not coasting) from 78 kept the bad vibrations going down to 72mph. At worst vibration speed, shift to manual and take transmission out of OD: At 78, I shifted into M5, rpms went up but vibration was same. If possible, gently swerve left and right to see if change in direction makes a difference: Gently swerving to the right seemed to add more vibration than swerving to the left. Accelerate to a speed that boarders on my comfort zone then brake gently down: Went to 94mph and back down to under 70mph. Smooth ride at 90+, vibrations came back but not as bad in brake assisted decelerating. Set cruise at worse vibrating speed and see if it stays engaged: Set at 78mph, the truck was vibrating badly and actually started lunging forward (new symptom?). So, this log is what I’m taking in on Monday. I hope to update the forum on the fix sometime next week, I have confidence that GM tech will get it fixed!