abominable z71

Every model year that comes out new people come here with the same problem and GM still hasn't come up with a fix. As far as trying to figure out what part is contributing to the vibe, if the dealership puts the truck on the PICO scope you need to get a copy of the results. Different components will have different frequencies at whatever speed you feel the vibration. The 70+ vibration is typically T3 vibration on the scope. This is not a tire balance issue. A tire balance issue would be a T1 meaning that their is an unbalanced mass in the tire and wheel assembly that causes a one "disturbance" per rotation. A T3 vibration is where things get tricky. This is a third order vibration meaning that for every rotation of the tire there is 3 disturbances. This kind of problem cannot be a mass imbalance and they assume the issue is out of round tires or force variation in the sidewalls or a combination. This is where the road force comes into play. It measures the variation in the stiffness of the sidewalls of the tire. These are the road force numbers that people talk about. So when they say 25 lbs what they mean is that stiffness of the sidewall varies by 25 lbs as the tire rotates, this variation is felt as a vibration. So they force match the tire to the wheel, they basically rotate the tire on the rim to try and minimize the variation, if they can get the numbers low enough they then balance the tire and this what the Road Force Balance is. It is 2 separate unrelated processes that get rolled into 1. Many people myself included have noticed the vibration is better or gone for a while but comes back. After it comes back they check the force variation again and it's different. Too many variables to account for, Tire pressure, temperature, tire break in, etc. the spring rate of rubber is constantly changing with these variables. The kicker is that this happens with every tire on every truck but only some have the vibration issues. many have swapped tires from trucks that do not vibrate and still have the vibration so whats the issue. 1 of 2 things. Either the vibration source is not the tires, possible, The hubs, rotors, axles all turn at the same speed as the tire. Or there is a resonance issue meaning that the vibrations from the tires are always there on every truck but only make their way into the cab on some trucks. This can be as simple as the body mounts which to my knowledge no one has tried replacing on a vibrator to date. This is what I would really like to see. Take the body mounts off of a truck that does not vibrate and install on a truck that does. Or it can be as complex as the metallurgy of the frame itself is just the right ratio of stiffness to mass that its natural frequency matches a third order tire vibration at 72 mph and shakes. Either way it has proven itself to be unfixable for almost all trucks that experience the 70-80 MPH vibration. Motor mounts, torque converters and so on. Try the truck at the same speed in different gears. 72 mph in 4th 5th and 6th gear if the vibration frequency is unchanged these are not your source if they were the vibration you feel you should feel significantly different because their rotational speed will be different. Example for a truck with 3.42 rear end and factory 275 55 20 tires at 72 mph the tire rotates at 759 rpm or 12.65 Hz. A first order tire vibration would be 12.65 Hz second order would be 25.3 Hz and third would be 37.95 Hz. At this speed in 6th gear the engine and torque converter is 1731 rpm or 28.85 Hz. 5th gear would be 36.85 Hz and 4th gear would be 49.81 Hz. If the vibration source was the motor or torque converter the vibration you feel should match those frequencies. Drive shaft: This is directly proportional to tire frequency by whatever rear end the truck has. 3.42 rear end would have a frequency of 3.42 times the tire. Same example as above, tire at 72 mph rotates at 12.65 Hz so the drive shaft rotates at 43.26 Hz. A drive shaft vibration due to out of balance would vibrate at 43.26 Hz at 72 mph. Bad pinion angle is a little different because the drive shaft is speeding up and slowing down as it rotates. Typically pinion angle causes a second order drive line vibration or a vibration of 86.2 Hz at 72 mph. These frequencies are speed related and would be lower at slower driving speeds I'm just using 72 mph for examples. The rear end. Vibrations from the rear end have been linked to the vibration in the 45-55 mph range and typically show as a 1st order tire vibration. This requires them to check the pitch line runout which is the backlash variation from tooth to tooth. It could also be excessive backlash between the coast side of the ring gear teeth and pinion gear which is why you feel it when you let off of the gas. The fact is GM knows there is an issue with this platform because there is a TSB addressing these issues with a bunch of band aids to try and fix it. But no definitive fix and often they'll go through the whole thing accomplish nothing other than having your truck in their service department for months usually you get your truck back in worse condition, meaning you hear many stories about scratches, dings and dents that were not there when you took it in, you made one or 2 truck payments on a vehicle you didn't drive for that time that has acquired an additional 500 miles or more, you're now in the same vibrating POS and all GM has to say is "operating within spec". Then begins the BBB or lemon law procedure, more attempted repairs, arbitration, shitty offers from GM like 1 months payment for a truck you haven't been able to drive for 3 or a few grand in trade assist but even the dealership doesn't want to give you decent value on your vibrating POS, then after many months and lost $$$ hopefully some sort of solution. Good looking trucks though, LOL.

The only way to check it is to open up the rear end and check the backlash. GM has a procedure that walks the technician through the process and tells them exactly what tools to use. IMHO this is work better suited for a shop that specializes in rear end work, they do it all day everyday and setup a R&P in their sleep. The dealership not so much. Unfortunately warranty only covers the dealership to perform it. in my experience when they do find rear end issues it's a bout 50/50 between swapping gears and installing a complete rear end and also 50/50 it fixing the issue. Some say new rear end...problem solved others say better but not gone. Good Luck

Agreed sounds like like there's too much backlash. The carrier bearing preload may have been to loose letting the backlash open up when the load is removed.

You will definitely rub the liner at full lock at the very least. Probably can get away with zip tie method to clear it. 285 65 18 on 18x9 -12 fuels rubs with 2-1/2" level but only the felt easily fixed with a zip tie.

The numbers from the road force measurements are the variance in force between the lowest measurement and the highest measurement due to stiff spots in the sidewalls and high and low spots on the tire and wheel.. 25 lbs is the industry standard acceptable measurement for a truck or suv tire although it has been stated that numbers below 15 are required to eliminate the shaking on the new GM platforms. Something to be aware of though as you drive and the tires start to break in there is a good chance these numbers will change and may require the tires to be force matched onto the wheel again changing temperature will also have an affect. Hopefully everything stays smooth for you from here on out.

That's what's crazy about these trucks My tires are 11.5" wide 32.5" diameter on a 9 inch wide wheel with -12 offset. So from hub face to outer edge of the tire is roughly 5.75" plus a 1/2" of offset. You got a 12.5 inch wide tire and an inch of offset for 7.25" off the hub face. I can guarantee you that set up would be in the metal on mine, I've seen the pics you posted and looks like you only get a light rub on the liner. I saw a guy in a parking lot running 325/60r18 on factory wheels with only a level and he said he only rubs a little bit. You never know what rubs and what doesnt until they're actually on the truck

No problem. I hear a lot of good stuff about the Mickey Thompson MTZ and cooper STT pro. I think I'd try to fit a 33 12.50 on 17x9 0 to slightly positive offset. Right now I have 285's on a 9 inch wheel and think the wheel is too narrow if anything. not sure if you find yourself needing to air down very often but the wider the tire and narrower the rim the harder it is to get the tire to squat so you can get the most use out of the sidewalls. A 2 to 2-1/2" difference in tire width to rim width works out really well. What wheel do you plan on running?

All three of those sizes on a -12 offset are right on the border where some guys will tell you they don't rub and others will say the do. My experience with 2-1/2" level and 285 65 18 which almost identical to the 285 70 17 you're looking at is on a -6 offset they never rubbed under any driving condition -12 rubs slightly at full lock in reverse when the suspension would compress. The 305 will most likely rub the liner but probably fixed by zip tying the liner back. The 33x12.50 is where you start getting to the point of cutting out sheet metal to clear. A lot of people say they clear on 0 offset or positive offset up to about +18 but I don't have any personal experience with 33 x 12.50 yet. I plan on running them once they come out in the Ridge grappler. For reference the 33 12.50 in a 17 is equivalent to a 315 65 17. The other question is how far do you want the tire to stick out and what type of tire do you plan on running AT, MT or hybrid? a 285 AT is typically narrower than a 285 MT Check a 285 65r18 nitto trail grappler 32.8"x11.93" versus a 285 65r18 terra grappler G2 32.56"X11.5". The same is true for the 285 70 17 trail grappler versus the terra grappler. The trails are about 3/8-1/2" larger both directions. Based on what you said the truck will see terrain wise, I'd look at the ridge grapplers, Cooper st maxx or Toyo RT. Just my 2 cents though.

Thanks, it's 3"ish suspension in the front 1.5"ish in the rear and 1.5" body lift. Started off as a 2-1/4 level and evolved from there and became a very expensive 4.5" lift but it rides really nicely.

I haven't seen anything and I don't think Nitto publishes weights on their site making it a little difficult to track down, I'm thinking they are going to be real similar to the exo grapplers as far as weight goes.

I think there's a pic in my gallery directly from the side before the 1-1/2" body lift was installed.

Same here, I have high hopes for these tires, They look super aggressive but are supposed to be really quiet. They do look like they might be pretty heavy though not too thrilled about load range F either.

So you are controlling the coil on the relay with power from the parking lamps as opposed to the turn signal wire and it still energizes the coil and opens the drl circuit when using the turn signal?

That factory wheels are hub centric with very little clearance between the pilot and the rim, It sounds like they were not properly balanced before someone could have incorrectly mounted them with the wrong cone and the wheel wasn't properly centered when it got balanced mounting on the lugs may have centered it up properly to correct the balance problem this would be more of a technician error. Aftermarket wheels are lug centric so this method would be better for balancing them.

Yeah that shouldn't move 1/8", sounds like the bearing is bad any signs of fluid leakage or is the shaft seal doing its job at least?

Do you have movement on the axle flange itself or are you getting movement in the rzeppa and tripod joint of the axle assembly? The inboard joint where the flange is located is the tripod plunge joint, its job is to compensate for the axle changing length as the suspension cycles. When the suspension compresses the axle needs to be shorter and the tripod joint slides in to accomplish this. The outboard joint is a 6 ball rzeppa joint. Both of these joints will have some play in them to allow the axle movement in multiple axis' during normal operation.

Any view you're looking for in particular?

You're not the first to have this complaint. GM's "we replaced and road forced the tires, everything's fixed you're good to go". Only to find out they made the problem worse than before and their response will be, well it's operating within spec nothing more we can do. BS

18 x 9 Fuel boost PVD chrome

285 with a -12 offset. GMC put's a coating on the underside of the SLT that protects the paint from road debris and chips pretty well. not sure if its on all models and chevy's as well.

i converted my lights over to HID, Built my own harness and installed Denso ballasts out of a lexus, no cap's were required. Zmny's issue is that the BCM is looking for a different resistance on that circuit because LED's function at a much lower voltage than what the BCM is looking for from the original halogens because the bulb itself functions as a resistor in the circuit where the LED is a diode. With a cap in the circuit once the plates are charged, in theory unless the capacitor breaks down the circuit should be open so if current is actually flowing through that circuit and providing power to the light the capacitor has broken down and the dielectric between the plates is function as a resistor. It's been 12 years since I took circuit's in college but if I recall correctly that's how a capacitor functions in a dc circuit. What you actually want is a resistor in the head light circuit to mimic the halogen bulb which is bascially the canbus corrector fishless is talking about.

Wrong thread

Pulsing current shouldn't happen on the slt models because they have a separate drl the truck only uses pwm on the sle low beam for the daytime running lights

And this to complete the Pepsi challenge 2015 headlights.pdf 2016 headlights.pdf 2015 headlights.pdf 2016 headlights.pdf 2015 headlights.pdf 2016 headlights.pdf 2015 headlights.pdf 2016 headlights.pdf

Going 305 65 18 BFG KO2 next time on the tires.