2014 Yukon SLT 4x4 5.3 - Ring & Pinion questions

[Charlie207]

Two questions:

How do I tell what size differential housing/ring gear I have in my front/rear ends? (not 100% on the terminology, so bear with me...)

and...

Basically, my truck feels sluggish, and I'm wondering if changing the ratios is a worth-while investment. I'm currently on 275/60R20 wheels/tires, and I'm told by Santa that my BBP tune should arrive this Saturday. Does it make sense to get it tuned via the back & forth datalogging/tuning before messing with mechanical stuff, or will a tune and re-gear be a better combo?

Here is a snip of the Mechanical Info when I do a VIN search for my Yukon, and it shows a 3.08 ratio:



I see these various versions when I browse Rock Auto, as examples, and it got me thinking about what size rear-end I actually have.



Thoughts/comments/concerns?

 

[swathdiver]

Two questions:

How do I tell what size differential housing/ring gear I have in my front/rear ends? (not 100% on the terminology, so bear with me...)

and...

Basically, my truck feels sluggish, and I'm wondering if changing the ratios is a worth-while investment. I'm currently on 275/60R20 wheels/tires, and I'm told by Santa that my BBP tune should arrive this Saturday. Does it make sense to get it tuned via the back & forth datalogging/tuning before messing with mechanical stuff, or will a tune and re-gear be a better combo?

Here is a snip of the Mechanical Info when I do a VIN search for my Yukon, and it shows a 3.08 ratio:

View attachment 345436

Thoughts/comments/concerns?

The front axle is 8.25" and the rear is 8.6" commonly known as a 10-bolt. If yours is a 4x4, if it has a single speed transfer case you have 3.08 gears. In your glove box is the RPO sheet, look for GU4 to confirm 3.08 gears. The other option was 3.42 gear or GU6.

If you re-gear, you will need an adapter or for more durability, a new rear carrier as the 3.08 ring gear uses a smaller carrier than the 3.23-4.88 gears.

Those tall tires make those 3.08s feel like 2.73s I bet!

I'm in no rush, but am going to change mine from 3.42s to 3.73s someday. Am also going to change the rear axle from the 10-bolt to a 14-bolt semi-floater which has a 9.5" ring gear.

According to my handy dandy calculator, your rpms are about 1465 or so at 70 mph, right?

 

[wsteele]

I have a 3.73 RA and roughly the same tires as you. My Yukon doesn't feel sluggish at all (stock tune), so my guess is if you go up (actually down but..) to something like 3.73 and do the BBT, you should have a pretty big smile on your face. Given BBT optimizes the shift points, maybe do it first before the ratio change, might be all you need to feel unsluggish again.

 

[Charlie207]

The front axle is 8.25" and the rear is 8.6" commonly known as a 10-bolt. If yours is a 4x4, if it has a single speed transfer case you have 3.08 gears. In your glove box is the RPO sheet, look for GU4 to confirm 3.08 gears. The other option was 3.42 gear or GU6.

If you re-gear, you will need an adapter or for more durability, a new rear carrier as the 3.08 ring gear uses a smaller carrier than the 3.23-4.88 gears.

Those tall tires make those 3.08s feel like 2.73s I bet!

I'm in no rush, but am going to change mine from 3.42s to 3.73s someday. Am also going to change the rear axle from the 10-bolt to a 14-bolt semi-floater which has a 9.5" ring gear.

According to my handy dandy calculator, your rpms are about 1465 or so at 70 mph, right?

I'll check the glove box area for the build sheet, but if it's a piece of paper you're referring to, it's long gone.

Good info on the carrier, I had to look up a diagram to ensure I was picturing the correct part.

I have zero experience with 2.73s, so I'll assume they also feel like a dog off the line.

I don't really have plans to step down in tire size, so I'll consider what you're plans are as way in the right direction.

As for highway engine speed/tire speed, I'm not sure off the top of my head; I work from home, and don't drive a ton. I'll have to go out and test this later.

THanks for all the nuggets of info/wisdom.

 

[Charlie207]

I have a 3.73 RA and roughly the same tires as you. My Yukon doesn't feel sluggish at all (stock tune), so my guess is if you go up (actually down but..) to something like 3.73 and do the BBT, you should have a pretty big smile on your face. Given BBT optimizes the shift points, maybe do it first before the ratio change, might be all you need to feel unsluggish again.

I agree with the idea to do the tune first, and get the engine optimized before throwing parts at it. (At this point I really only see a catback exhaust in my immediate future)

Where I live is very hilly, and almost zero flat stretches.... you're either going up or coming down while constantly turning to some degree. Even though the transmission seems to shift smoothly, it has only one goal.... to shift to 6th ratio as quickly as possible. This is as annoying as poison ivy on your *******.

My hope is that the tune helps remidy most of the driveability issues.

 

[wsteele]

I agree with the idea to do the tune first, and get the engine optimized before throwing parts at it. (At this point I really only see a catback exhaust in my immediate future)

Where I live is very hilly, and almost zero flat stretches.... you're either going up or coming down while constantly turning to some degree. Even though the transmission seems to shift smoothly, it has only one goal.... to shift to 6th ratio as quickly as possible. This is as annoying as poison ivy on your *******.

My hope is that the tune helps remidy most of the driveability issues.

I have a four speed and live in a similar terrain situation, mine seems a little better than yours sounds, it will hold in the lower gear like when going uo hill, but I am pretty certain if I had a BBT it would perform better.

 

[swathdiver]

My hope is that the tune helps remidy most of the driveability issues.

It certainly will, just remember to express your concerns and desires to Justin and he'll know how to tweak it to your liking. As the computer learns, it will get even better after time.

The RPO sheet is a sticker on the left side of the glove box, bunch of 3 digit codes and such.


As for gear ratios, the lower the number, the higher the ratio and the slower the car will be off the line but will turn less rpms at speed. Technically they would also allow for a higher top end speed. 3.42s are a good all around ratio and 3.73s maintain 3.42 performance when going to a taller tire. Our Sierra rolls on 35s and has 3.73s but it's effective ratio is very close to 3.42s. To recover the lost performance, someday this one will get 4.10 gears.

 

[Charlie207]

The front axle is 8.25" and the rear is 8.6" commonly known as a 10-bolt. If yours is a 4x4, if it has a single speed transfer case you have 3.08 gears. In your glove box is the RPO sheet, look for GU4 to confirm 3.08 gears. The other option was 3.42 gear or GU6.

I just ran outside to check my glovebox, and this is what I see...



Fourth row down, fourth column over: I see GU6 listed. So that means I have the 3.42 final drive ratios, right?

 

[Charlie207]

The front axle is 8.25" and the rear is 8.6" commonly known as a 10-bolt. If yours is a 4x4, if it has a single speed transfer case you have 3.08 gears. In your glove box is the RPO sheet, look for GU4 to confirm 3.08 gears. The other option was 3.42 gear or GU6.

I just ran outside to check my glovebox, and this is what I see...



Fourth row down, fourth column over: I see GU6 listed. So that means I have the 3.42 final drive ratios, right?

 

[wsteele]

I just ran outside to check my glovebox, and this is what I see...

View attachment 345541

Fourth row down, fourth column over: I see GU6 listed. So that means I have the 3.42 final drive ratios, right?

Right. The BBT should fix you right up.