jcchevy

Never seen the "gas cap less" feature. Can you take a pic of it? does it still have the "threads" to screw a cap on?

@PMmury, only if experiecing a rumble strip type hum/feel between 55-72mph. I see on prev post you had the less then 55mph issue which would not apply to the front and sounds like you got that taken care of via rear axle resolution. I must have misread and thought you were experiencing new issue. It is funny how some of the different distuiquished issues are determined by common speeds, which is helpful in narrowing at least where to start looking. The dealer can also hook up a vibration analyzer on the powertrain components to distinguish the faulty area. Im pretty mechanically inclined and had my issue narrowed down to the front diff, was just a matter of convincing dealer. Since the wheels still turn on the truck, its not considered broken/faulty to them.

What you have described (tiny rumble strip feel) is your front differential. Needs replacement or complete overhaul. You may find this thread /post linked below more useful and related. This is not the resolution to all, but for those SPECIFIC to "tiny rumble strip" feel issues, its worth reviewing. We have several members (including myself) who got their dealerships (NOT EASY) to replace the entire front differential assembly, which resolved the issue and for most part trucks rode smooth as glass again. http://www.gm-trucks.com/forums/topic/154976-2014-sierra-humming-noise/page-9?do=findComment&comment=1607902

@kylek , yes - see my previous post 65 , heres direct link to it. Its way better then the original though, even tolerable, but yes it did come back , same hum, same speed range etc.. @majikgoats - this first 9 digit number is the part number, the last bottom is the UID (unique ID) , the others not so sure. I broke out the numbers, in case others are searching for any components of this tag, it will lead them here. ================== original > replacement AACJ > AAAZ = not sure what that is 23186399 > 23484385 = OEM GM Part number (my original and new replacement 1yr later were both 23186399) appears your replacement was an updated one, possibly just to account for 2015 yr model (although its same diff specs), but could be updated/better quality control etc... 9430100000000M > 9430100000000M = same number, not sure what that is GMC a2132826aacj7745 > TRMF B2143156aaaz0837 = UID, not sure what the GMC / TRMF means though. ==================

I seen that too, but the 1500 series, including the 6.2L engines, share the same front differential and PN. The more reason about the higher trim packages is that 3 out of 4 trucks (read that in an article) are purchased with higher trim levels.

Well, after almost a year and half (thread started 11/2013 by Oli4) and engaging with most of you on here. I thought it would be appropriate to tally up the numbers. After a lot of persistence, many have found a resolution requiring a complete front differential replacement or overall. Let me know if I miss-spoke for anyone. Front Differential complete Replacement: gm-guy > 2014 Sierra CC Denali 6.2L 4x4 3.42 gears w/z71 package, kylek > 2015 Silverado 4wd z71 kgweststar > 2014 Sierra CC SLT majicgoats > 2014 sierra 1500 CC 5.3 4x4 LTZ 3.42 gears Front Differential Overall: Oli4 (original thread starter 11/2013) > 2014 Sierra All Terrain 4x4 rudie20 > 2014 Sierra Others pending (denied / need a better dealer / in troubleshooting progress / could have been fixed but no follow up) warmie@245 fishermen71 > 2015 4x4 5.3 z71 kylek > 2015 Silverado 4wd z71 saltybrad > 2015 GMC 2500 Denali rollcenter > 2014 Silverado CCSB 5.3L Z71 RM4665 UCR Boot > 2014 Sierra SLT 4x4 gSwift > 2014 Sierra 4x4

Hi @rudie20, if you read in previous posts, you will see I received a complete new front axle assembly (although 6 months ago) and so did another. Maybe they are going through the complete front diff assemblies too fast to keep up?? Only takes 1/2 hour to replace a full front diff assembly vs many hours to repair one, set gear alignment and the like. For those having the issue and want a resolution, you can buy your own entire front differential assembly (applies to both 2014/2015 1500 series trucks) for around $1K , its simply a bolt on installation for the most part. http://www.gmpartscenter.net/oe-gm/23186399 Of course, since its the same OEM GM product (same manufacturer making these), its probably going to have a 50/50 chance being built with same issues/problems giving you a humming machine, or blown hole through your diff as @rudie20 achieved. I would love to find a aftermarket beefed up one to replace it entirely. There are not many (ok, none) qualified axle shops around my area I would have undertake that, otherwise I would do that route.

@Oli4, congrats on being persistent and basically getting a new front diff in order to resolve it. Welcome to the new front differential club. We all must have got a bunch of Friday made differentials. But your are right, did something externally cause this, or did the manufacturer of the diffs gearing really sucked it up lately (AAM i believe). Since these are the same front generic 1500 series GM truck front diffs/ part numbers going back in previous models.

Good luck Oil4, I know you been dealing with this even before I did, unfortunately there is no GM case or bulletin out there for a "defective front differential". If they use chassis ears properly they should be able to pin point the noise/hum is coming from front diff, thus replacement of the front diff is the resolution. Its just hard for them to swallow replacing a $1500 part while its not technically "broken".

Glad to hear. Good feeling isn't it? the return of sanity Just wanted to make a note, I have updated my Differential part numbers I previously posted, both original and 1yr later replacement were both Part# 23186399. When you get a chance check the sticker on the outside of your front diff and see if the part number is the same. If it is, you have a 50/50 chance (like i did) of it being defective. My new one is defective, but its not as bad as my last one (yet). I am actually looking for an upgraded /aftermarket front differential. I have the bigger rear differential due to the 6.2L engine, but they didn't touch the front diff. if anybody knows of an aftermarket (purchase entire front diff, install myself) type of company, let me know.

Correct. Its a difficult situation GM puts dealers and customers in. As long as the wheels go round and round, the diff "isn't defective" Thats why all the guys with the particular symptoms/ issue are out of luck for a resolution to their issue unless they truly break their front axle.

(EDIT, I originally jotted down incorrect part number, that was actuallty for the GM diff lube) this post is now updated with the correct part #) I custom built to ordered my 2014 denali, picked up from dealer Nov 2013. Front Axle Part number was (23186399). My brand new replacement front axle part number was the same. ( which was installed Nov 2014). You can check on the sticker on outside of your own diff to check part number. And from my research its the same front axle (and part number) that was in the previous 1500 series generations. Just think they (drive line assembly manufacture line) quality really went down hill or even more specifically a huge batch of bad carrier bearings. Because how coincidence to have two axles (1 yr a part, not to say it wasn't from 2013 and just sat on a shelf at GM for a year) both bad, one little better then other, but still both same issue.

(EDIT: Updated Correct Differential Part Number) Thanks for the detailed description majicgoats, Thats important on these forums. If you bought used, the previous owner probably was sick of that issue as well and traded it in. Based on your descriptive issue, you have a defective front axle. You can read my previous posts on this topic. My first one became defective around the 4K mile mark, a year later I was able to twist (hard) the arm of the Service Dept , got them to replace it finally (they are a good service dealer, but per GM they don't suppose to replace front differential if its still functional, which technically in GM's terms it was) and the issue was resolved and no more noise. Was smooth as glass. That excitement was unfortunately short lived, about 1K miles later the new diff (same part number as previous as i took pics before after, only SN changed) started the same thing, only good thing is its not as bad as the first (yet). Below are some info in regards to what (IMO) is the root cause which would be a defective carrier bearing going bad/bad defective part in the assembly line and would cause this rumble strip vibration humming noise. There is currently NO service bulletin, There is currently NO resolution from GM. Front Axle (entire axle) part#:GM Part No. 23186399 ($1000-1500) part. Description of issue and fix=what GM should do Belly Growl Problem: Low-pitched growl emitting from the axle at speed. It can sound like tire drone, and you may not notice it at low speeds. Sometimes accompanied by vibration. Fix: If it’s a carrier bearing it typically requires a total axle rebuild because metal shavings have probably damaged other components in the differential. However, in rare cases if it’s caught early you may get by with just replacing the carrier bearings. Rule of thumb: If the carrier is loose, the axle will probably need to be rebuilt. Resource from: http://www.fourwheeler.com/how-to/transmission-drivetrain/129-1207-identifying-bad-axle-noises/#ixzz3RLoOOryZ

Update on the NEW front differential that had originally resolved this issue. After roughly 1,500 miles the issue has returned unfortunately. Same exact humming/rotational moaning noise as before. I have not taking it back in, don't have time for this at the moment and don't expect them to replace it again as they stated before there is no TSB currently for this and they need one from GM. IMO, I think some front diff's are coming with bad pinion/gear backlash (countless other threads seen same issues with REAR axles) and settings from the FACTORY. So with the bad settings it takes some time before it creates enough "play" incorrect teeth wear etc..and leads to what we all are currently dealing with. There are some TSB's for the rear axles, just wish they would release something for the front axle so the dealers arms are not tied. If a TSB doesn't come out for the front differentials / axles by this Spring, I will be putting my truck up for sale and may have to retire my user ID.