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2015 Tahoe rear gearing
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Post 2015 Tahoe rear gearing 
Hey folks, decided to make an official thread on this. I intend to replace the rear gears in my 2015 Tahoe, switching from 3.08s with a G80 to 4.10s with an Earton Truetrac.

I've found a shop I halfway trust at this point. From my discussions with them, the Tahoe has a 12 bolt rear with the 9.5 inch ring gear, not the 9.76 ring gear. Seems the 9.76 ones go behind the 6.2 while the 9.5 goes behind the 5.3. In any case, the problem is the same for both, no Eaton Truetrac. However, it looks like it is a simple swap-in if I use a G80. The guys at the shop are saying that I will need a ring gear spacer to put a Truetrac in, and they are strongly recommending against this as it is not a strong part. They say they'll put one in if I really want to but it's not a good idea.

From what I've been able to see, it looks like the rear suspensions are the same between the 07-13 Tahoes and the 14-up Tahoes. If this is the case, the 14 bolt from the 07-13s DO have an Eaton Truetrac available. So my question for the board is, is there any major difference between the last gen Tahoe rear suspension and the current gen that would prevent me from getting an older axle and swapping it in? I plan to do my own research, of course, but some of you guys seem to walk around with a parts interchange manual in your heads.

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This is looking good so far. Per Rock Auto, all the rear suspension parts I've checked on a 2010 and a 2015 have the same part numbers. The different years have different types of parts listed, but where there is both a common part name and brand the part numbers are all the same. Next step, visit my local u-pull-em yard with a tape measure. Here's hoping they have a 14 bolt from a 2013/2014 and older plus a 2015 or newer 12 bolt in stock.

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good luck! this sounds like an easy swap with the final result being what you want...

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Except I'm thinking not, now. A whole diff swap for a rear that will rob more HP doesn't make too much sense when looking at my plans for the vehicle. I think I'll be better off for now going with the driveline shop's recommendation of a G80 with 4.11s using all GM parts. In a year or two Eaton ought to catch up.

I'm not doing this to put big power under the hood so I'm thinking now that a 14 bolt will be overkill. The 5.3 will be staying as is and if it goes out I'll probably put in a 6.0 or a 6.2. Mainly the Tahoe is just a family putt-putt but I'd like the ability to tow a load. Considering how big a slug it is just pulling itself along with a 3.08, I wouldn't want to put a trailer behind it. Besides, I have so many projects now, both automotive and house/land, that I'll have to work for 20 years after I die just to wrap them all up.

For anyone that's interested though, it looks like there are three options for the 2014+ having Tahoe/Suburban folks with the 12 bolt rear.

1. GM parts, G80 limited slip or open diff, can put in whatever rear gearing you want.

2. Convert to an older 9.5in setup. This requires installing a ring gear spacer, which is highly NOT recommended by the shop I plan to use. If interested though, here's a writeup on how to do it. https://eastcoastgearsupply.com/files/PDF%20Files/gm9-5-12-bolt.pdf

3. Install a 2007-2013 14-bolt. From what I can see using Rock Auto, it SHOULD work but I have no idea if anyone has done this anywhere.

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Hey Jim, I do know that some of the gear makers make thick and thin ring gears so that spacers are not required for the different breaks in ratios of some of the rearends. This is different than your potential issue of requiring the spacer for the install of a Detroit Trutrack in your ride.

If you aren't planning on blowing doughnuts or powersliding at every curve, then the Eaton Gov-Lock (G80) is an excellent traction aid. The fact that it disengages the clutches above a certain speed was always a plus in my book when setting up my girlfriends/Moms trucks for daily driving duties. I wouldn't feel comfortable sending either of them out on Winter roads with the Eaton LSD(or Eaton POSI as Eaton calls it clutch packs that don't release) or any sort of Detroit Locker.

Since your 15 has the 12 bolt 9.5" ring gear rear end, any OEM G80 will be a larger unit than the G80's used in the 8.5"/8.6" that we are used to trashing.

I've got over 200,000 miles on my 97 ecsb Chev Silverado with the stock 3.42's G80, AND the original m4l60e(knock on wood). The G80 still works fine, is quiet and provides 2 wheel action when I need it.


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The 5.3 with the 12 bolt cover uses the 9.5" ring gear and 33 spline axles

specs
GM 9.5" rear with 12 bolt cover and 33 spline axles. 5.3L V8
Ring Gear Diameter: 9.500
Cover Bolts: 12
Ring Gear Bolts: 12
Spline Count: 33
Dropout: False
Pinion Support: False
Carrier Breaks: 3.23 / 3.42
Rear Suspension: Solid
Pinion Nut Size: 32mm


The 6.2 with the 12 bolt cover uses the 9.76" ring gear and 33 spline axles.

specs
GM 9.5" rear with 12 bolt cover and 33 spline axles. 6.2L V8
Ring Gear Diameter: 9.500
Cover Bolts: 12
Ring Gear Bolts: 12
Spline Count: 33
Dropout: False
Pinion Support: False
Carrier Breaks: 3.23 / 3.42
Rear Suspension: Solid
Pinion Nut Size: 32mm


I'm thinking the specs in relation to the ring gear diameter is incorrect for these rear ends, one has to be 9.5" and the other 9.76" as it doesnt make sense for them both to be 9.5".

Yukon gear makes an open carrier for these 2014+ rearends and they are exactly the same for the 9.5 used behind the 5.3 and the 9.76" units used behind the 6.2 liter engines. $436 for either unit.

They offer 2 part numbers:
Yukon Standard open loaded carrier for '14 & up GM 9.5" & 9.76", 3.23 & down - YC G40090727
Yukon Standard open loaded carrier for '14 & up GM 9.5" & 9.76", 3.42 & up - YC G40090728

This leads me to believe that the only thing that is stronger about the rear axle assembly that is used behind the 6.2 liter GEN-V SBC rpo L86(420hp@5600rpm/460lb/ft@4100rpm) is the increased diameter of the ring gear(when compared to the vehicles that use the GEN 5 5.3 liter V8 rpo L83 rated at 355hp(gas) and 376hp(E85) both @ 5600rpm/383lb/ft@4100rpm and 416lb/ft@400rom(E85). This is very similar to the older 7.5"/7.625"and the 8.5"/8.6" rear ends. If they need a tad of extra strength, simply tack on a bit of diameter.

Even the GM(Eaton)Govlock(G80)-GM 23156744 is the same for both the 9.5 and the 9.76" applications

Gov loc positraction for GM 9.5" 12 bolt and GM 9.76" - GM 23156744 ($634)

This has been an interesting exercise into some of the newer rear axles. On my 2007 trailblazer since it has the 293hp inlne 6 LL*engine it got an 8.0" 10 bolt rear with an optional G80. If it was equipped with the GEN-IV 5.3 it would have gotten the 8.6" rear axle assy with a G80. Then if equipped with the GEN-4 395hp LS2 engine, it would have gotten the 9.5" 14 bolt SF rear end, but the optional traction device was not the G80 with the energizing clutch packs, it used rpo G86 which was similar to the Eaton LSD where the clutch packs are always in play and axle differentiation occurs only once the clutchpack preload is overcome.

The new traction aids in the form of the electronic rear axle posi's in the newer Camaros and Vettes are very interesting and are wringing every last ounce of traction from virtually every situation found on the road.

peace
Hog

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Thanks Hog, your post as always was very informative. I agree on you with the specs not being right, it looks like whoever made the original source you used inadvertently copied the 5.3 specs under the 6.2 specs. In any case, the way I drive the Tahoe is completely different from how I drive my other cars. I usually drive the Tahoe like Grandma's Grandma but the Silverado and the Corolla, I dog them out like there's no tomorrow. I'm hoping that this gear change will help it to not feel like such a large rig, and the next mod I plan is a 3/5 or a 4/6 suspension drop. The thing sits high enough that I have to step up into it, and the wife practically needs a step ladder to get in. Nice thing about not having to change rear ends is I can get an off-the-shelf lowering kit instead of having to figure something out.

I sent an email to the shop to get the parts together and contact me for a day to get the job done. When it is I'll post up the results. Gotta start playing with the program now, so it'll run right with the new gears.

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Hi Guys...just buzzing by today...

Clarification on the Eaton G80...it is an open diff until the centrifugal spins above 200 RPMs.

Then it kicks in the clutches to become a locker

Older versions had that governor set above 200 RPM and when it kicked in...to much power was at hand and grenade'ing it a high possibility

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Bummer. It's a lot harder to make a gearing change in a 2015 model than in a 2000 model. I have a question posted on the EFI Live board to find out how. Specifically, how to recalculate shift points for the new ratio.

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I want to say when I rebuilt the rear in my truck several months ago I saw “conversion” type races or bearings to switch between the new and old carriers.
I still have the Eaton and 4.10’s from my 98 tahoe and considered using them when my daily 2k silverado started whining.
Ended up not wanting to waste $700 worth of parts on the old work truck though and just replaced bearings and ceramic coated new races and old ring/pinion. Mine turned out to just be a bad pinion race and got to it in time so all good hard parts.
I was looking those parts up for a 10 bolt also,but surely they make same for 12b if they changed much new/old.

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I don't know what all GM did with this stuff, but it appears to be some new design to replace the 14 bolt. With any luck, this means they have the strength of the 14 bolt with the driveline loss of the 10 bolt. At any rate, we're going to go with the 4.10s and the G80 for now and will just hope that at some point the Truetrac catches up with the new stuff. I've asked the shop to get the goodies together and then we can set an install date so this should be done sometime in the next two weeks.

I also figured out the EFI stuff, I think, and I made a post there on how to do it on the 6 speed transmission vehicles. Hoping I have it right. BTW, I post as Telco over there.

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All parts except bearings are in. Tentative install date is Thursday, unless there is a problem getting the bearings in. Shop said something about a backorder on them.

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A delay, bearings did not arrive. Project on hold until they come in. Once the shop has all parts in hand they will call me and we will arrange an install day.

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Keep us posted, sounds like fun once installed!!

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Any updates?

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Dropped the Tahoe off at the shop this morning. The only issue I'm seeing at the moment is EFI Live gave me a Reduced Engine Power alert on the DIC after I stuck in the new program. Checking with the EFI Live folks right now to see if they can look at the program and find any problems. A check around the board shows that the speed limiter may be set outside the computer's allowable limits, something to do with OnStar not liking the speed limiter maxed out. When I go back down I will see about loading a program with factory speed limits in to see if I can get this corrected. Might be the problem because when I first loaded a modified program I had the same problem. Then, I just loaded the factory program back in but never got back to investigate.

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Update - the shop says they are finished but I don't have a ride to pick it up until tomorrow afternoon. They said they will store it in their shop overnight and I can get it tomorrow. The shop said that the gears set up perfectly, unfortunately there is a very slight whine on decal between about 60 to 55. They can only hear it with air and radio off, and looking for it. They also said that the DIC Reduced Power alarm is still there but the Tahoe didn't drive like it's in limp-home mode. I'll report back initial impressions tomorrow night.

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I have the Tahoe back now. The new gears are great, only negative is a slight gear whine on decel, 60MPH to 50MPH. It's still a slug, but now it's a slug with a big S on its chest. Laughing The 5.3L is just not enough engine for the weight of the vehicle. With a curb weight of 5308lbs, 355 hp @ 5600 rpm, 383 ft-lbs. @ 4100 rpm equals 14.95 pounds per HP and 13.86 pounds per TQ, which is far from muscle car territory. The better multiplication certainly helps though. When the engine goes I might put a 6.2 in it, but I have no plans to make any major engine changes at this time.

It's too soon to comment on mileage. While playing around with it on the way home I got into it with one of those Ford Focus GTs that are supposed to be hot stuff, and I walked away from him at highway speeds. He made 2-3 attempts at it, and he was only able to catch up when I let off. Normally I ignore little FWD irritants like this but seeing as I wanted to see how it would do at WOT anyway, I went ahead and played with it. Up to about 80 or so it pulls harder but it starts running out sooner than it did over 80, as expected. Before it seemed like its preferred highway speed was 90 to 95MPH, now its preferred highway speed is around 75MPH.

Had the work done at Harmon 4x4 in Tulsa, they seem pretty knowledgeable and on top of their game. I plan to start using them for differential work in the future since my last go-to guy retired and left the business to his son, who seems to be quite a bit less capable than his dad, to be nice about it.

All in all, I'm happy with the results and would do it again.

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How is your 0-60 now?

Im guessing low 8

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Dunno. Definitely faster than it was. I might make a run to the local drag strip on test and tune night to see how it does though.

Of course, I might not. Razz

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The Engine Reduced Power error is gone now. I changed the top speed limiter to 240MPH. For some reason the computer allows for 314MPH but doesn't like it if you actually set it for 314. I calculated the theoretical max at 207MPH, which is how fast it would go if it had enough engine to turn 6200RPM in 6th gear, so it's not like it'll ever hit 240.

This project is complete.

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