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4.56 gears K2XX 4x4 L83


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Yesterday I dropped off my 2014 Sierra 1500 5.3L V8 4x4 at the differential shop (Ring and Pinion of Oakland) for new ring and pinion gears. I went from a 3.42 to 4.56. My truck has 70,000 miles on it.

 

Once the diff covers were off they found my rear carrier bearings had no preload. He replaced the bearings and used the factory shims but still found it resulted in no preload. All bearings were replaced and shims were added. He said the pattern on the rear 4.56 gears was perfect (Yukon gears).

 

He said the front diff preload was loosening up and that typically means the bearings are on their way out but still had some life left. He recommended replacing them now if I was able to, which I did. The front gears are Motive 4.56.

 

I updated the computer for the different gears using a TruXP tuner (stock tune with modifications for tires and gears) and began driving to break them in. Some immediate observations are the driveline now feels solidly connected to the engine. If the engine downshifts, I can feel it just like downshifting a manual trans. If I tap the throttle, it immediately engages and transfers power to the wheels. There is no lag or “chuggle.”

 

The increased leverage of the new gears reduces engine strain so much that the truck runs in V4 most of the time (this is the break in period so I am driving very conservatively) and my gas mileage has improved about 30% because of this. The rear gears are nearly silent. Sounds no different than the factory 3.42 gears.

 

The front gears can be heard. It’s not obnoxiously loud, but can be noticed. If one wasn’t familiar with my truck they may think it was normal road or tire noise. Since it’s the front gear, I’m not really worried about the noise because most of my miles will be in 2wd. When I am using 4wd, I’m usually doing something where function is a priority, crawling out of a snow bank, pulling a stump, etc...

 

Of course I wish it was silent but knew there was a likelihood that aftermarket gears would be noisy. Overall I’m thrilled so far and looking forward to finishing the break in period.

 

I’ve got a new 5” driveshaft being built by shaft masters. Should be done by the early next week. With the new gears, I wanted a higher critical speed than what the factory shaft provided. I’m not a fan of driving around anywhere close to the critical speed and from my calculations, the stock shaft is about 4500RPM and my new shaft will be 6381RMP. (Additional info: With a 4.56 gear ratio, the driveshaft will hit 4500rpm when the engine reaches 2925rpm in 6th gear. For reference, the engine runs at 2175rpm when traveling at 70mph in 6th gear.

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Vehicle Info:

2014 GMC Sierra 1500 SLE All Terrain

Crew Cab, Short Box

5.3L V8 Flex Fuel

4x4 with G80 Locking Rear Differential

275/65R20 Cooper STT Pro Tires at 50psi (33.5” measured)

Wheel/Tire weight: 115lbs each

4.56 Yukon Ring & Pinion (rear)

4.56 Motive Ring & Pinion (front)

All gear bearings and seals replaced

 

TruXP Xtune Plus Performance Tuner (same as SuperChips FlashPaq F5 Item# 2845) running the stock tune with options. Options selected are:

1.) Modified tire size to 33.5”

2.) Updated gear ratio to 4.56.

 

 

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9 hours ago, imiller1974 said:

Nice. I'm on the fence about having my 3.08's swapped for 4.10's. East Coast Gear Supply quoted me $2316.64 to do it. They're in Raleigh, I'm a 30 mins south of Charlotte, so a 3.5 hr drive.... It'll take 8+hrs to do it.

I just had this done about a week ago. 3.08's and 33's were terrible.

changed em out for 4.10's, used all the recommended yukon and aam parts from east coast gear. the truck feels like it should now.

def worth doing. all an all i spent right at $2400 with synthetic fluids an all. just do it.

everything the op said is true. i dont understand why gm uses such gear in these truck, my millage has gotten significantly better as well.

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Grumpy - so far it seems to be functioning fine. I haven’t adjusted any shift points on the tuner, it’s still the stock settings. It’s not searching for gears. Downshifts are much more noticeable and effective to slow the vehicle down.

 

Ski - I haven’t taken it on the freeway yet. Right now I don’t drive more than 20 miles before letting it cool down. I’ll take a short trip on the freeway tomorrow and get back to you.

 

Centex - If you found a shop that is willing to install your own parts you could probably get it done for a little bit cheaper. The cost of my parts through the shop was over $1200 and labor was just over a grand. I probably could have bought the parts online for $800. To me it was worth it to have this particular shop do the install and give them the ability to order exactly what they needed. Everything is warranted by them for a year and I get peace of mind that the job was done right along with knowing the money went somewhere local.

 

If you’re going to do 4.56, you may want to consider a new driveshaft. With 33.5” tires (actual measured diameter, not factory new specs), the driveshaft will self-destruct around 95mph. The reasons why someone would be traveling that speed are another topic, just know, if you hit that speed, it’s almost certain the shaft will catastrophically fail.

 

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8 hours ago, 300 Blackout said:

Grumpy - so far it seems to be functioning fine. I haven’t adjusted any shift points on the tuner, it’s still the stock settings. It’s not searching for gears. Downshifts are much more noticeable and effective to slow the vehicle down.

Going back to your first post you mention a HUGE increase in fuel mileage. This hand calculated? 

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Going back to your first post you mention a HUGE increase in fuel mileage. This hand calculated? 


No, it’s not. There are too many uncontrolled variables in my driving habits to give a truly accurate estimate of fuel efficiency, so take my numbers with a grain of salt. Most of my driving is city and I use both E85 and gasoline. The computer says my average has been 12mpg over the last 6,000 miles, so that’s what I’m going to use as my starting point.

I just put in 23.75 gallons of 87 gasoline and I’ve driven 2 miles from the gas station to home. I’ll hand calculate this tank and post my results.


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51 minutes ago, truckguy82 said:

We all know it’s not

Patients grasshopper, patients. 

 

If his starting point is 12 mpg on a factory DIC which are 8 to 10% happy, he has only one way to go, eh? I was drawn by the comment about the AFM duty cycle. That's what go my attention. 

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