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abominable z71

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  1. abominable z71
    Did they tip the pinion angle down or up 2 degrees? You should be able to see the shim between the spring and rear block probably about 3/16" thick on one end and comes to a point on the other , if the thick part of the shim is towards the front of the truck they tipped it down 2 degrees.
  2. abominable z71
    So I got an email from GMC after my visit to the dealership to take their survey, just a bunch of check boxes, but at the very end they had a nice fill in the blank section which must not have a character limit because I wrote them a nice a little story about my dissatisfaction and the dissatisfaction of many others. Filled it out about a week or so ago and got a phone call today from GM. GM Rep: "This is blah blah blah from GM and I read your survey response, I understand your frustration and I;m just calling to let you know that we are fully aware that many of these trucks have vibration issues at and above 70 mph's. We would like to assure you that our engineers are working on and are very near a fix for this issue, we are asking you to please be patient a little longer as a fix should be forth coming." Me: "This has been going on since 2013 how much longer is it going to take to fix this issue?" GM Rep: " I don't know" Me: "Whats causing the problem?" GM Rep: " I don't know" Me: "Are they trying to figure out a way to hide the problem because they can't fix it?" GM Rep: " I don't know, but we are expecting a fix to be released soon and anyone experiencing the issue will be able to go to a dealer and have it repaired." She then offered full use of GM's beach house in Wyoming, and told me that the 2016 sierra will be powered by a cold fusion reactor because they are really close but don't quite have the perpetual motion machine dialed in, maybe the 2018 redesign.
  3. abominable z71
    No problem, Operating within spec, what a joke. F@!K GM, I will never buy another GM product, should have never bailed their sorry a$$ out and let their crappy products go under with the rest of the company.
  4. abominable z71
    The entire rear end and front diff for the matter is built by AAM a former subsidiary of GM, they are the oem supplier for all three major domestics on at least some models.
  5. abominable z71
    Just got a phone call. Nothing wrong with the gear, that small chip is not in the contact pattern and does not affect performance, backlash is fine, gear pattern is fine, nothing more we can do. He did say the area rep is going to be at the dealership today and he's going to try and have him drive the truck with the PICO scope even though last test with the PICO said vibration is below the limit. The service manager has actually been really good pushing the boundaries of what he's allowed to do under GM's warranty. When it's all said and done I'll probably be told operating within spec and sent vibrating down the road. If that's the case this will be the last GM product I purchase.
  6. abominable z71
    My intention was to measure backlash, While I was rotating the case measuring runout I noticed the chips in 4 teeth took pictures and stopped there. Measuring the backlash on 41 teeth is a PITA especially on a hypoid gear tooth. Spec for back lash I believe is .007-.013" with .008" being ideal, and the difference in backlash between teeth is .003" or less. I called the service manager and gave home the whole run down of it being put on the PICO but being below GM spec, so they vector matched and RF balanced the tires but it didn't solve the problem, I told him I opened up the diff and found chips and took some pictures and asked if he wanted me to email them to him so they could decide how they wanted to proceed, He said bring it in first thing tomorrow morning. The truck is in at the dealer as I type this, waiting for a phone call to see what they have decided to do.
  7. abominable z71
    I have the highway vibration problem still not fixed. Opened the rear end and found teeth with chips in the heel waiting to hear from the dealer what they plan on doing about it, they would not inspect the rear end on it's first trip in for vibration issues because the vibrations were below GM's spec, so I opened it myself and took pictures to send to the service manager. Trucks 5 months old, no paint or body issues at this point. Slip yoke clunk is there like it has always been in GM 4x4s they need to go back to a fixed yoke on the t-case with the slip yoke in the driveline like they had in the NP203 and NP205 t cases of the 70's. No problems with the AFM v4 mode. G80 rear has a ton of backlash and slop in it. Interior pops and creaks with thermal expansion, very loud pop from the center stack area when its hot and the AC starts cooling down the interior. hood release lever rattles on the freeway. Trim pieces on the center console rattle if your leg touch's the console while your driving. It is a beautiful interior though, best looking on the market IMHO. No electrical issues or radio problems, everything works well, I have the bose system though not sure if that makes a difference when it comes to issues others are having with the radio. I would enjoy this truck much more if it didn't vibrate at freeway speeds. I love the exterior and interior looks and features but it definitely is lacking in mechanical quality in some areas and lacking some features available in other trucks.
  8. abominable z71
    Opened the rear end this weekend and checked things out. 4 teeth had chips that look like this. This was the worst of the 4. My vibration may be within spec but we shall see if gm feels this gear is within spec, I suspect the heat treatment wasn't up to par and makes me question the overall quality and tolerances of this gear set.
  9. abominable z71
    What you describe is why I haven't pushed the dealer in trying to fix the vibration. I figured more problems would be created than fixed. I haven't been able to fix the problem but I haven't made anything worse or created any new issues, but at least eliminated some potential sources. Too bad a new rear end costs $2000, might just end up with another out of spec POS rear end. I considered buying a complete 9.76 with 3.73 ratio since no one makes a 3.73 gear set for these new 12 bolts but leery about it being a vibrator, even considered a used 2013 rear end, but who knows what kind of cluster that would be to swap in.
  10. abominable z71
    After swapping tires today off my buddys GMC the vibe is still there, same speed same frequency, I have pulled the front cv shafts so the only thing in the front that could cause it would be the front hubs, run out was good, possibly wheel bearings, In the rear, measured run out on the hubs everything was good. Vibration frequency is too low to be a prop shaft with a 3.42 rear end if you have the 3.08 a first order prop shaft could look like a 3rd order tire vibe on the scope. I doubt it's bent axles as that should show up as a run out issue in the hubs. All that is left is the ring and pinion or differential. I noticed this morning when both my friends truck and mine were up on jack stands his rear end seemed much tighter less play in the gears and also a lot smoother, when turning the wheels by hand it just felt like it took a lot less effort to turn everything. Everything is pointing to a rear end problem. Hopefully the techs at your dealership are competent and set-up the ring and pinion properly, it's a time consuming process and easy to get wrong if you don't do it often, and I doubt rear end rebuilds are done very regularly at dealerships. When I open mine up for inspection if I find a problem I'll take mine to a local shop here called Fearless Gear, they specialize in differentials and are known for having a really good reputation for very high quality work. I'd rather pay out of pocket and be confident things were done properly.
  11. abominable z71
    I like the new lights and front bumper on the sierra but I think they messed up the grille. Hopefully the new 16 tail lights fit the 15's those look really sharp, not sure how I feel about the new bar led's in the 16 but, led head lights would be a nice upgrade.
  12. abominable z71
    pinion angle responding to the trailer weight?
  13. abominable z71
    Good luck Jesse, tomorrow I'm swapping wheels and tires with my buddy that has a gmc cc 4x4 that rides smooth. We shall see how that turns out. Either some trucks are more sensitive than others or the wheels and tires are not the problem. He has BFG ta ko2's on factory 17 inch wheels.
  14. abominable z71
    This is a number that I don't think you can get with any accuracy. Some people may have it and not notice it, some it is very mild, some trucks might never see the speeds where the vibration occurs so they might have it but you'd never know. For me and others it starts right at 70 mph and up on smooth asphalt. Where I'm at the speed limit on the freeway is 70 mph and has just been repaved recently so I get to experience it everyday on the way to work and everyday on my way home. Do yourself a favor and get a RAM, If I could go back in time and do it over again I would get the RAM. My vibration problem didn't show up until about 2000 miles. So don't think just because the test drive went well that you're in the clear.
  15. abominable z71
    This is a number that I don't think you can get with any accuracy. Some people may have it and not notice it, some it is very mild, some trucks might never see the speeds where the vibration occurs so they might have it but you'd never know. For me and others it starts right at 70 mph and up on smooth asphalt. Where I'm at the speed limit on the freeway is 70 mph and has just been repaved recently so I get to experience it everyday on the way to work and everyday on my way home. Do yourself a favor and get a RAM, If I could go back in time and do it over again I would get the RAM. My vibration problem didn't show up until about 2000 miles. So don't think just because the test drive went well that you're in the clear.
  16. abominable z71
    Definitely the hardest part of trying to pin down the source. The vibration come and goes in it's severity but never goes away. I think tire temperature might play a part but sometimes its just as bad when it's hot as when it's cold. I think it might be a phasing issue. Sometimes the tires are in sync and the vibrations are at their worst after a while of driving and making enough turns they get to a point where the vibrations cancel each other and you just don't know where they are in relation to each other until you hit the freeway and see what kind of vibration you get. This would be an extremely difficult thing to test unless you have your own perfectly straight 5 mile stretch of super smooth asphalt to run up and down so you could clock the tires relative to one another and drive strait ahead.
  17. abominable z71
    Do you have any info on the bracket recall?
  18. abominable z71
    Yeah I read that, thought it was interesting because I noticed the vibration was typically worse when it is cold. Do you have anymore info on it. Does the switch light up or does it notify you in the cluster that there is a 4wd shit in progress? I wonder if it does it without any indication that it's happening. My u-bolts were loose when I checked them took about 1-1/2 turns to get them to 75 ft-lbs, didn't affect the vibes though. I have noticed something that bdkfl mentioned when they were test driving new trucks, that trucks that tended to vibrate at freeway speeds also had a vibration at 4500 rpm when you put your foot into it, I have noticed my truck vibrates at 4500 when I get on it and that it vibrates at highway speeds, trying to decipher what that might mean. There is no doubt a cause for this and either GM can't find it or they know what it is and it's an expensive fix so they will just fight it out hoping the owner will give up. Either way it's a bunch of bull$h!t
  19. abominable z71
    It would definitely allow the the rear end to rotate up and down more than typical but the spring perch with the centering hole is welded to the axle tube so torquing them to the proper setting should center the axle back on the perch. although the more things you measure on these trucks I don't think there is anything that is level, plumb, square, round, flat, flush, aligned, concentric or balanced, so it's a huge assumption the perches are aligned and parallel. There is no doubt some slop, Fireaxxe pointed out his thrust angle changed a quarter of a degree by loosening things changing the working angle, then putting everything back where it was and re-torquing everything. An alignment shop can tell you what the thrust angle is, they are usually small and require laser equipment to measure.
  20. abominable z71
    Maybe you should try a bottle of smart water instead of aquafina. J/k gotta keep a sense of humor with these trucks though otherwise they'll drive you nuts. I'll do the water bottle test on my 5.3 this weekend and take a quick video. What rpm does the 4.3 idle at? My 5.3 idles at just a tick over 450 RPM.
  21. abominable z71
    Being that there have been so many different sources for the vibrations caused by parts made by different manufactures, I would say it is almost certain they will just damp the vibrations to make sure they are not making their way into the cab, this is the one thing GM has control of in house, change the cab mounts and steering mount to eliminate the transmission path, perception is reality, no perceived vibration...no vibration, at least until parts start to fail.
  22. abominable z71
    My understading and anyone that feels different please chime in. A positive angle is when the portion towards the front of the vehicle is higher then the rear. In fires case +4.5 for the engine & tranny means the output shaft on the tranny is pointing down 4.5 degrees (centerline points down towards the rear) +3.5 on the drive line, the driveline pionts down towards the rear at 3.5 degrees creating a working angle of 1 degree between the transmission and driveline with the 1 degree difference being an open angle on the bottom side. Basically a \/ in the side view. A -2.6 angle on the pinion I would think and fire can confirm that the front of the pinion is pointing down at 2.6 degrees. This would create a working angle of 6.1 degrees also in a \/ side view which in theory would vibrate like crazy because the angles compound to 7.1 and don't cancel unless the pinion rotates significantly under power. If he meant 2.6 degrees with the front of the pinion pointing up the working angle would be .9 degrees with a side profile /\ and the two angles would almost cancel each other at .1 degrees. My measurements were +3 transfer case, +1.4 drive line +.8 pinion with working angles of 1.6 \/ front and .6 \/ rear with a difference of 2.2 degrees . I added 2 degree shims to the rear and the results was +3 tcase +1.3 driveline +2.2 pinion. working angles 1.7 \/ front .9 /\ rear. This just created a worse vibration, so perhaps the static working angles need to be significantly out to compensate for spring wrap and acceleration and so forth. I'm going to pull the shims and possibly flip them around and tip the pinion down and see what that does. On a different note I pulled the front CV axles and replaced them with outer stub shafts to test and the vibration was not changed, pointing back the rear end and most likely the ring and pinion. Next weekend the rear end is getting opened up and inspected. Probably should have checked there first.
  23. abominable z71
    Fire, Did you measure the working angles for the rear drive shaft before making the adjustments to the transmission and adding the wedges? If so what were they, I'd like to compare them to mine. My working angles were 1.6 down in the front and .6 down in the rear. I added 2 degree shims in theory that should roll the pinion up to have a working angle of 1.4 up almost zeroing out but it didn't seem to affect the vibration much, I still need to measure the angles to see what affect they actually had. Thrust angle might still have the u joints out of wack, something to look at, I also got grease leaking from every cup on both u joints, the underside of the body is speckled with grease. Time to make an appointment with the alignment shop and check the thrust angle. Glad I sprung for the lifetime alignment.
  24. abominable z71
    Improper working angle causes the drive line to speed up and slowdown 4 times per revolution to account for the u joint angles not cancelling each other out on both ends, out of phase drive shafts will cause the exact same problem even without the pinion shaft rotating up or down. This video is worth a thousand posts:
  25. abominable z71
    Weight distribution from the front to rear wheels will change with the slope you're on. On flat ground all of the vehicles force (weight) is vertical. The normal force which is the force perpendicular to the road and the vertical force are the same and the vehicles weight contributes no force in the horizontal direction. As you tip it up on an angle the vehicles weight creates two forces one vertical and one horizontal and the normal force is reduced in relation to the angle of the grade (vehicles weight x cos(angle of the hill)). The steeper the grade the lower the normal force, this is why the steeper the hill is, the easier it is to slide down (friction coefficient times normal force, no normal force, no friction). In order for your truck to not slide backwards due to this new horizontal force it creates a moment about the rear. What this has done is effectively moved more force into the rear springs causing them to compress further add acceleration into the mix and some axle wrap and your pinion flange rotates up. Get on the brakes going down hill and you will have the reverse case but even more exaggerated because the truck is already front heavy.
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