Please be advised this is a lengthy post but it may help you eliminate some issues if you read it all.
I have a 2017 GMC Reg Cab 2WD Base with 5.3 as my company truck. We bought 3 of these trucks slightly used all with very low mileage. Mine had 5,600 miles on it. When I first drove the truck from our shop I noticed the vibration immediately at all speeds but it was almost scary violent at 67 mph and above. It never smoothed out at higher speeds. I mean like everything in the truck was vibrating, keys rattling, armrest shaking bad. Called our "fleet manager" who bought the truck he said he hadn't noticed. However our VP drove it once and noticed so they had the tires balanced before I ever picked it up. They added 9 OUNCES to the front tires. I took it to tire shop they re-balanced and ended up with 3 ounces. My guess tires were flat spotted from sitting and have worked their way back to round after driving a couple hundred miles. Unfortunately the tire balance did nothing for the vibration and I quickly realized it was all coming from the rear. I also noticed the pass. side rear sat 2" higher than the drv. side and the drv. side front sat almost an inch lower than pass. side front. The truck also pulled to the left slightly. We have a very observant "fleet manager". Being as I was working 2 hours from our office and 3 hours from the dealer we got the truck they told me take it to a local GMC dealer, so I set an appointment and they got me in just a few days later.
Dealer got on the horn with GM engineers and were directed what steps to take next through the whole process. First was surprise surprise RFB (road force balance) of the tires. No results. Checked pinion angle, rebuilt the rear end. The flubbed the rebuild so had to order a second kit and do it again something about messed up shims. The 2nd rebuild changed nothing so GM sent them a whole new axle assembly. I suggested they check the frame since the truck sat so crooked. They said they did and it was good. Changed all the springs and rear shocks which brought the truck to the typical "Chevy Lean" of 1/2". This however did not help vibration. Next was a new driveshaft, followed by new rear rotors. I think they did about twelve more RFB and a handful of alignments before telling me it was done on DAY 93. Yes you read that right DAY 93.
I went for a test ride with the service manager and at first I thought the vibration was gone but after a couple miles it started to show its ugly head. It seemed to get worse the further we drove although it was at least half as bad as before if not better. Still not right though. The service manager acknowledged it as well and seemed very disappointed as he just continued to ramble on about how he will never be reimbursed from GM. Not my problem although I did sort of feel bad for the guy. I mean we didn't even buy the truck there. Back to the shop. Back on the horn with GM. Now they are telling them to warm up the tires on a trip and then hurry up and do the RFB. LMAO I am just thinking when did dealerships quit being a service shop and start being a tire shop. This is like the umpteenth time they have balanced these tires. I mean the lug nuts are literally half rounded off by now. However after doing the RFB on warm tires they called me stating two of the tires are just a little out of spec and they were going to order them and asked if I would like to replace the other two on my dime. No thanks they are junk tires anyway and I had planed to upgrade as soon as they fixed the truck. So the SM tells me they are going to replace the two tires and if that doesn't fix it GM is going to call it a normal characteristic of the reg. cab long bed 2wd truck, telling me due to the light rear end it is going to have added vibration. I tell him the other two identical truck we bought do not vibrate nor do any of our other 20-30 Chevy and GMC trucks with the same configuration in our fleet of work trucks. This told me they were done. They ordered the tires not once but three times. They had to go through 4 new tires to get two that spec out good. Bridgestone should be ashamed.
Day 109 went to get truck and take it for a test ride. They have put more miles on the truck than I have and had burnt though a whole tank of fuel. On fumes the dealer says there is a gas station about a block away so we pull in to this full service station and he says "Do you want me to put a few gallons in it?" It was near full when I dropped it off almost 4 months ago and he wants to buy me 3 gallons. NO I will get it I have a company card so what do I care. I tell the woman fill it up. About 20 seconds later I hear "Sir I think you have a leak". I get out and sure enough the $1.37 she just pumped was running down the inside of the bedside and dripping onto the ground. Through all this work they had obviously unhooked the filler neck and failed to reconnect it. Unable to continue our test drive with no fuel back to the shop we go. At this point I am concerned that this service department is just incompetent, with the fuel neck and messing up the rearend rebuild. I have told our fleet manager everything that was going on and that they were pretty much done. He got in touch with the dealer we bought the truck from and explained everything that had gone on. They seemed eager to make this right. FM made arrangements to bring me up one of our junk yard trucks the following week to take mine back to the dealer we got the truck from. The dealer quickly fixed the filler neck and called the next day to come get it. Now I am done with them so I stop at the Enterprise to drop my rental off before I even test drive the truck. When I get there the SM says "are you ready to take it for a ride I had my guys put 5 gallons of gas in it so it would be ready". I tried not to be a [email protected]
and said as politely as I could "no you made it pretty clear you are done pissing with it so I will just fix it elsewhere or do it myself." I thanked him for his efforts, signed his lengthy invoice with a total of $0 and left.
Any way I took my truck home for the weekend and it was considerably better than the original vibration. I would say it was about 50% of what it was originally. So that weekend I decided to crawl underneath and check the pinion angle. I checked the transmission output angle and compared it to the diff angle as these should be close to parallel. Mine were 2.4 degrees different. I told the dealer it was going to to check it out. They called our fleet manager a few days later and said the truck was done, all good. I rode up (nearly 3 hours from my home) with our fleet manger to get the truck. When we arrived I asked what they had done did they shim the axle? They said "We RFB the tires and aligned it". I nearly pissed myself laughing as I asked him, was it out of spec? The guy says "yeah I'm pretty sure it was". I asked if they checked the pinion angle and he said no need it was all good. I asked him "you actually drove the truck at 70-75 mph when it arrived and you felt the vibrations and now you don't at the same speeds?" He said "yep all good". Alright off I go. Interstate was only about a half a mile away but when I got to the end of the entrance ramp I was doing 75 mph and their alignment and RFB sure did KNOCK IT BACK A PEG. The vibration was probably back to about 70% of what it was from day one. On my long teeth chattering way home I called the dealer asked we had just left from and told them they didn't do anything but make it worse. I went on to question "when did a mechanic turn into a technician and does technician just mean parts changer?" I asked why they didn't look at the pinion angle it was at least worth a look right or wrong.
On my way home I picked up some 2 degree shims from a spring shop. Installed them over the weekend drove to work Monday and found that it had dramatically reduced the vibration. I was probably now at about 20% of the original shake. So after 110 DAYS in the shop, who knows how many techs looking at it plus GM engineers directing them to invest $13,000 in labor, parts and a rental vehicle. I have gotten considerably farther with my 5 minute diagnosis and 45 minute repair with my $23 shims. I have since replaced the factory tires and wheels with aftermarket rims and AT's that I had RFB at a tire shop. I even went with a 265/65 instead of the 255/70 which is like a half inch shorter and an inch wider thinking it may change a frequency. This did nothing to eliminate the remaining vibration but it looks better and I no longer get stuck all over the jobsite. I have also played around with spring clamps in various locations. I even made my own using 3/8" thick plate on top and bottom with grade 8 bolts. Some configurations seem to help a little and some make it worse. I can tell you one in front of the axle about 5 inches and one directly behind has been my best results. I believe the front of the axle makes it better because it is actually helping the pinion angle which is still not parallel to the transmission output. I also think the one directly behind the rear is helping to tighten the spring pack. I tried one front and rear both out about 6 or 7 inches each way made the truck extremely harsh and only intensified the vibrations. My next move is going to be getting rid of the factory block and the 2 degree shim. I plan to replace that with a 1 1/2" block with a 2.3 degree taper built in to it and new U-bolts, It is a kit I have found on Amazon.
In closing if the truck never gets any better than it is now I can live with it (especially since I didn't pay for it) but I will continue to try and resolve it. I will post what works if I succeed. My advice to others is until there is a fix that is acknowledged by GM and they actually release a new TSB to fix it, don't even bother taking it to them. Their solution is RFB and alignment. Sort of like the HID headlight shake. I told my dealer after the third trip (on my personal truck) that it was faulty bulbs. I replaced them with some good aftermarkets and problem solved. However if you go to your dealer today and complain of shaking headlights they will show you a bulletin from GM stating it is just a characteristic of HIDs. My job truck lights shake as well. Any truck with the Phillips D5S bulbs does. I had two different rentals in the 110 days, both Chevy and both lights shook. What we find for fixes never makes it back to GM. They would rather spend money a handful of hours in labor on the handful of people that complain than have a recall on millions.