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Well I ordered all the parts this morning to do the rear axle shafts and brake job.  Truck has 81,XXX miles on it.  Factory pads are about gone.  The passenger side axle shaft seal is back to leaking pretty bad.  It was R&R'd at 16k and has been sweating ever since and the dealer didn't want to hear it.  9 months later when I bought our new Enclave, I made sure I didn't step foot in that dealer. Anyway, I've also had the driveshaft balanced by a local shop which helped out quite a bit.  All but one person who I've found did Yukon shafts said it fixed the vibration.  So for $260, worth the old college try.  Parts list en route are.... 

 

-Yukon Axle Shafts

-ACDelco Wheel bearings (both sides)

-ACDelco axle shaft seals (both sides)

-GM Diff cover gasket (yes I know its reusable but I've already used it once with my PML Cover and put silicone on it. )

-Raybestos Police package rotors.  I read that these are mill balanced to a pretty good spec.  Tolerances in general are much tighter. 

-Raybestos hybrid ceramic truck pads

 

While I have it apart I'm going to do a gear pattern check, R&P backlash check at multiple locations around the ring AND check the pinion pre-load measurement.  I read that one of these lemon buy back vibrators was donated to a tech school and upon disassembly the pinion pre-load was zero.  Yes, zero.  So i'm going through the axle my way. 

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Wow no wonder GM spent $1 billion to set up a new axle plant in Michigan for building the 12-bolts. The quality coming out of AAM since they moved to Mexico has not been impressive. The quality control is all over the place.

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I didn't even know that.   I looked into it... Yes, new axle location in MI.  The chebby chakes might of had something to do with that....

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Well these shafts are on back order from Yukon.  ETA is late July. 

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Does not look like Yukon has an ETA for these axle shafts.  I emailed Yukon to find out more... see if they had any info.  Just got a canned "not ETA" email back.  Does anyone know where to buy these 2014+ 12 Bolt axle shafts?  I cannot find anyone else making them. 

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I canceled my order THR night and then Friday morning I get a shipment email notification from JEGS.  Called to make sure they did not divert the shipment and reinstate my order.  ETA is this WED.  We'll see if they sent the correct # shafts and if so I'll be thrilled. 

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Did you check run out on the existing shafts?  Just curious if you KNOW you need shafts or if it's just an experiment?

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Sorry if I missed it but it's not clear in the text. Why are you swapping axel shafts? Is it solely for vibration? I'm planning to regear at some point in the future and seems like it may be worth a shot if this can help alleviate some of the vibration in the truck. Any other upsides? (assuming vibration is a thing that is being fixed with this)

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Posted (edited)

Trying to fix the highway vibration in the arse end these trucks have.  I've found some posts on you tube where the Yukon shafts did fix the issue.  Figure for the price and effort its cheaper  and worth the shot before trading the truck in on a new F150. And, if it works.... I'll have stronger Chromoly shafts. I'm going to check gear pattern, backlash in multiple places and pinion pre-load while I have it apart. I really think its something within the new 12 bolt axle.  just stink its my daily driver and don't have the ability to re-built the axle from the ground up.

Edited by FL335i
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Posted (edited)

Well I got it taken apart and put back together today.  I'll upload pics tomorrow in the AM, it's been a long day. 

 

Setback # 1.  Yukon has the wrong part # listed for our axles!!!  The part # listed on its website for our 2014 + 9.5"/9.76" is YAG23199121 which is 34-5/8" long.  The shafts I took out of my axle today were the same kind, but 34.02" long.  So I called up jegs and am in the process of swapping out to the correct part # YAG15812663.  This part # is listed as 2007+ 9.5".  This was an option on the previous generation 1500 with he 6.0L and tow pkg IIRC.  I almost bought one in '08... 

 

I continued on, replaced the bearings and seals.  You can search previous threads of mine, at 16k my RR axle seal went and blew gear oil all over the place.  At 40 something thousand it started "weeping".  Dealer would not do jack so I've been driving it.  Fast forward to 83k I'm at now, it's leaking bad again.  What I noticed on the right side  was that the axle housing was molested.  Burrs, nicks, scarring etc.  No idea how the inside and outer axle tube end could have that much damage.  I spent about 30 minutes with a file, sand papers and cleaned it all up nicely.  This is where the seal sits.  So if I installed a new seal, as you drive it in, the burrs are not providing a smooth surface for the metal seal body.  This probably explains why at 16K the truck started leaking oil out the RR axle.  So glad when the dealer repaired it they took the time to see WTF at brand new truck was leaking gear oil.  Guess I finally answered my question.  Ok, so now we have the axle tube cleaned up, new bearing and new seals installed. 

 

Next, I open the GM TSB for the vibrations on our truck.  I go to the section where they go over the rear axle.  The TSB tells you to check EACH TOOTH of the diff for backlash.  Variations between each tooth cannot be more than .002".  I checked backlash at each tooth.  No more than .001" variations if any.  No issues here. Pass.

 

While checking backlash, the TSB indicates that the spec range for backlash is .003" to .010", but they RECOMMEND .005" to .007".  So the old target of .006" BL.  Guess what my backlash is?  .011".  Almost twice what the TSB is targeting for BL.  When building my previous axles in other trucks, I always target .006".  And I used the same dial indicator I've used to setup all my previous axles.  I never would close up an axle with .011" of BL.  So I take the ring gear and carrier out.  the TSB was nice enough to provide the bearing cap torque specs (63 Lbs/Ft).  There is only one large shim on each side.  I measured them and was trying to see if I could swap them to get the ring gear closer to the pinion, but that's how it was already setup. I have leftover Yukon shims from my '89 Blazer's front 10-bolt built, but the bearings on the new 12 bolts are much larger.  So this issue of excessive BL needs addressed.  I need to order some shims and get the BL to the .005"-.007" window the TSB recommends and that has been the gospel BL spec for years. 

 

While the carrier is out, I check the pinion for preload.  32mm socket if anyone is wondering what size the nut is.  I found the pinion preload to be perfect.  I was reading on my 1/4" drive beam inch pound torque wrench 12-13 inch lbs.  If you look up the spec for a "used bearings" 10-bolt or most other axles it's 6-9 inch lbs.  I like preload, it's good...   my pinion is setup correctly. 

 

Gear pattern check.  So with everything back together and my out of spec sloppy .011" BL, I do a gear patter check.  Pattern looks pretty good, no complaints.  But the pattern does hint at the excessive BL reading.  The pattern was a bit shallow.  So when the BL comes down to what is should be, the pattern will probably look perfect.  So this was pretty good... no real complaints.

 

Being I had to re-install my OEM axle shafts, I cleaned up the bearing and seal area with some sandpapers.  I used 1000 and then 2000 grit.  They needed it.  Just something that should be done because what I noticed is that when dealing with the C-clips, the axle has to be pushed inward quite a bit, and the seal rides up on the axle shaft to an area where it normally does not ride and if you have a bunch of dirt, debris or worse a bur it will damage the new seal on re-install.  So I cleaned them up really well being I had to re-install them with my new seals already in. 

 

I also installed new rotors and pads.  The OEM brakes went 83k and I still had some pad left, but the rotors were warping.  I went with Raybestos Police Rotors and Raybestos Truck & SUV ceramic pad.  I compared the rotors to the factory ones I took off.  The factory rotors had 57 vanes.  The new rotors had 58 vanes.  Next difference was the thickness of each plate.  the center air gap was noticeably smaller on the new rotors, indicating a much thicker plate while maintaining the overall rotor thickness.  These rotors came with the nice zinc coating like the rotors I used to buy for my BMW's years back.  Rotors look like a nice and easy upgrade from the factory part. I cleaned out the caliper slides which had black grease in there.  I used the same stuff I used on my BMW's.... bright purple HIGH TEMP Ceramic brake grease. Good for like 900 Degrees or something stupid like that. 

 

TO BE CONTINUED.  Once I have the correct yukon axle shafts in hand along with some carrier bearing shims....  I'm going back in.  BL adjustment and new Axle shafts and this axle will get my blessing to be "closed up".  From what I saw today, I am 99% convinced the vibrations we are getting in the new trucks is from this new axle.  And from what the TSB is indicating to check on the rear axle GM knows it too.  These new 12 bolts were built in a AAM Mexico barn. 

 

 

 

 

 

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IMG_1821.JPG

Edited by FL335i
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The last time I tightened up the backlash on a rear differential, it went out about 20k miles later.  Once the gears have taken set, I would advise not changing backlash or making any other adjustments.  Maybe you'll get lucky, I guess I would advise just be careful.

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I hear ya.  I've re-used gears in axle builds and never had issues.  Whenever the gear setup is changed, I treat it like a new diff and "break it in" and then flush the oil once or twice. 

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