G80 replacement

[Fifty]

I’m debating a gear change on my 2015i GMC Yukon XL.

I have the 3.43 gears I believe.

We don’t do much freeway driving… however when I changed my 3.42 geared colorado with the 8l45 (same gear ratio as our 8l90) to a 4.56 gear set…. I actually got 2mpg better on the freeway.
It made 6,7 and 8th gear usable at speed.

Anyways, I’m considering a numerically higher gearing for the our XL. Since I’ll be doing a little more off-roading and I’ll be towing an off-road trailer.

Since I’m doing that I’m considering a new diff… I was initially going to go with an Eaton e-locker. I’ve had two vehicles now with them and like them way better than the arb I had before.

However I do like have an lsd… getting both tires gripping on the street with out having to flip a switch is nice.

I am considering a mechanical lsd/locker like a Truetrac…. These vehicles are heavy enough back there to tame them.

Anyone have any experience with anything other than the g80?

 

[number9]

I’ve had the G80 in vehicles since 1999. Never had an issue with one, they just work when they’re needed.

Having said that, those vehicles weren’t “wheeled”, just general driving and getting in wet grass, dirt, or mud when it had to be done.

Recently got a ‘22 F-250 with the E-locker and I don’t like it. It works fine and all, but I just don’t like having to engage / disengage it when it’s needed. I’d MUCH prefer to have the G80 in the Furd.

 

[Rygrego]

3.08 is standard. 3.42 was optional. Check your RPOs for ratios. G80 stands for locking diff not ratio. If you have a GU4 it is a 3.08.

 

[OR VietVet]

3.08 is standard. 3.42 was optional. Check your RPOs for ratios. G80 stands for locking diff not ratio. If you have a GU4 it is a 3.08.

You beat me. The G80 is the locker and not the gear ratio.

To answer the original question, I like my G80 in my z71 and the only other locker I have had experience with is a very harsh Detroit Locker in my purpose built rock crawler years ago. When that thing locked in, you knew it.

 

[Fifty]

Yea. I just couldn’t remember which gear ratio it is exactly.
The g80 is not so bad. And when they work they are fine. Ours goes into full lock up but only when there is wheel spin.

The problem with that is when off-road you don’t want multiple rotations to induce a lock up. For one that’s a lot of stress but also it can keep you or dig you into more trouble.

Hence the selectable locker. And as number9 pointed out, the down side to selectable lockers is when you need both tire traction in unforeseen events… it’s not good.

Hence the trutrac… they require less wheel spin to engage so less negatives than the g80… and also have full locking ability.

The question is: does the suburban or Yukon xl have enough girth to make the trutrac style diff smooth?

 

[OR VietVet]

I have had friends that swear by Tru-Trac lockers for everyday and light off roading. If I remember right, they are made by Detroit Locker. I don't think you can go wrong with Tru-Trac but it also depends on how hard you are on your equipment.

 

[mrpeterclark]

The shops tell me the Eaton Truetrac does nor work in reverse? Is that true? I'm about to re-gear mine for 35s and the shops don't like G80s, say the Eaton doesn't work in reverse, and the Yukon Grizzly is loud and harsh for daily driving... I like an auto locker, but maybe an E locker is better? Not sure what fits the 10 bolt though. I don't want to mess with air.

 

[Doubeleive]

The shops tell me the Eaton Truetrac does nor work in reverse? Is that true? I'm about to re-gear mine for 35s and the shops don't like G80s, say the Eaton doesn't work in reverse, and the Yukon Grizzly is loud and harsh for daily driving... I like an auto locker, but maybe an E locker is better? Not sure what fits the 10 bolt though. I don't want to mess with air.

I have never heard of that, could be true but seems like it would have came up before, also seems like that kind of detail would be noted by every single re-seller I would reach out to eaton to confirm/deny

 

[duke90]

The shops tell me the Eaton Truetrac does nor work in reverse? Is that true? I'm about to re-gear mine for 35s and the shops don't like G80s, say the Eaton doesn't work in reverse, and the Yukon Grizzly is loud and harsh for daily driving... I like an auto locker, but maybe an E locker is better? Not sure what fits the 10 bolt though. I don't want to mess with air.

I think the ARB RD222 is the one needed for the 2015+ yukons/suburbans if wanting to replace the G80, but I will call ARB on Monday to confirm.

 

[Marky Dissod]

I’m debating a gear change on my 2015i GMC Yukon XL.
I have the 3.42 gears I believe.

We don’t do much freeway driving ... however when I changed my 3.42 geared colorado with the 8l45 (same gear ratio as our 8l90) to a 4.56 gear set ... I actually got 2mpg better on the freeway.
It made 6th, 7th and 8th gear usable at speed.

Anyways, I’m considering a numerically higher gearing for the our XL.
Since I’ll be doing a little more off-roading and I’ll be towing an off-road trailer.

If you have the 6L80E, 3.73 works well with it in SUVs.

 

[Fifty]

It’s the 8l90
Which has 3 overdrive gears. 6,7 and 8

 

[swathdiver]

It’s the 8l90
Which has 3 overdrive gears. 6,7 and 8

What size tires are you running? That motor is going to hum with 4.56s on stock tires.

 

[Marky Dissod]

If you've already a 3.42 rear axle, and the 8L90E, you really don't need to step up to more than 3.73.

Multiply your 3.42 rear axle, by 8L90E's 1st gear.
My DESIRED rear axle would be 4.10, times 4L60E's 3.06 = 12.54, for a frame of reference.
Do the same for 8L90E's final overdrive gear of 0.652.
For me, 4.10 times 0.7 = 2.87. Effectively I'd be improving city MpG to sacrifice highway MpG.
That's why I'd prefer 3.90 - which I don't think they make? - to 4.10, since I don't tow or offroad.

3.42 * 4.56 = 15.59 Your present 1st gear
3.73 * 4.56 = 17.01 Your 1st gear with 3.73 rear axle
4.56 * 4.56 = 20.79 This may break something, and make 1st gear too short, might as well be a seven speed
You REALLY don't NEED any more 1st gear torque multiplication than 3.73 will provide.

3.42 * 0.652 = 2.23
3.73 * 0.652 = 2.43
3.73 might actually save fuel on the highway, unless you enjoy speeding over 70MpH (as I do).
4.56 * 0.652 = 2.97
4.56 won't save any fuel on the highway (nor in the metro / urban).

If you want more axle than 3.73, 4.10 would be more than enough.
For best results, tune your ecm & tcm for the gear change, especially to improve the transmission's personality.

 

[Fifty]

Yea, I need to do the math like you just did. There is a really good website that breaks a gear comparison down with rpms, speeds etc etc etc. Tons of data.

Im running 275/65/18 cooper ATP tires right now. The goal is 35's eventually so my two trucks and the trailer can share spares. But even technically with my truck lifted (Border patrol suburban rear springs and ADS coilovers up front running about 1/2 inch lower than the rear) I am not sure the cutting will be worth making 35's fit.

Maybe if a decent set of small fenders that have a good liner or if Dirt kings ever makes their liners cheaper...

Ok back to the gears. I was shocked at the MPG increase I got on the colorado when going 3.42 to 4.56... and stock tires. However this 6.2l and the current 3.42 is really good once you hit 75 mph. That being said 50-70 is just eh ok. because it hunts gears any time its not flat.

I had not settled on 3.73 or 4.10 gears. I wanted something that keeps the pinion strong (4.56 on the d44hd/M220 on the zr2 the pinion cant safely get smaller than the 4.56 ratio. I wanted 4.88 for 37's). But I figured if I was going to change gears, I would look at two things and its pretty silly really:

1) which gearing kept the speedo as close to correct with a 33 inch or 34 inch tire. I live in commiefornia so correcting the speedo and not having to run a tune, or buy a boat load of credits on HPTuner and load/reload tunes every other year sucks.

2) Since anything higher numerically than stock will get me better mileage on the city streets and the freeway, find a number that didnt make 1st stupid on cement and actually makes 1-2 and 2-3 shifts in 4wd low usable because the shift pressure tuning etc etc is very complicated and I dont know any 4wd trans 8l90 tuners that are any good for the crawling stuff. High speed pre runner stuff yes... crawling... which is really "Im camping and towing an offroad trailer and going slow up a tricky section and need the truck to be in low crawl mode not spin the tires on each shift flare" mode

So yea, that and as much as I like the G80... its quite nice when they work and mine seems to have been built nice and tight, I would like to have a locker in the rear. I dont want an arb, been there and they fail open which sucks, and air lines leak and get caught on stuff. OEM Eaton E lockers are on two trucks, and they have been awesome other than the BCM from GM makes engagement delayed. So either an e locker or a TruTrac.

On the street and on fire roads etc, a trutrac or other (grizzley etc) are sufficiently open enough when you dont need a locker. But when you need it, man, they work. The suburban is heavy. I wouldnt want them on a lighter car although I had a 3100# Subaru with their version on my front diff and an OS Giken on the rear (which is similar to the G80...kind of...sort of)

But having a tight lsd (or locking lsd) in a pinch is better than a locker if its not a crawler in my mind. My TRX has that e locker and in Baja mode (75 rear 25 front power split) and sport (70/30) the rears just spin and it goes from both to one to the other spinning. The traction control makes it a pretend locker (same with front which is an open diff) but it just gets annoying.

Long winded... I need to do the math for stock gears and tires to new tires

 

[MrTris]

I'm gonna be an аhоlе and bump this -

How'd it work out, OP? What did you eventually end up doing?

I'm looking at Eaton rear diff and getting mixed answers - Grok says the forums swear by the Eaton LSDs, so, I'm sold, there, but, getting mixed signals on part numbers.

Grok says 914A538 and Summit has 917A732 - which is correct? Grok is often wrong on stuff, so I'm inclined to trust Summit, since it's confirmed it fits my Yukon.

Had anyone replaced their rear diffs with an Eaton Trutrac Helical LSD? If so, what was your experience?

 

[OR VietVet]

I'm gonna be an аhоlе and bump this -

How'd it work out, OP? What did you eventually end up doing?

I'm looking at Eaton rear diff and getting mixed answers - Grok says the forums swear by the Eaton LSDs, so, I'm sold, there, but, getting mixed signals on part numbers.

Grok says 914A538 and Summit has 917A732 - which is correct? Grok is often wrong on stuff, so I'm inclined to trust Summit, since it's confirmed it fits my Yukon.

Had anyone replaced their rear diffs with an Eaton Trutrac Helical LSD? If so, what was your experience?

Call Summit and give them the 2 numbers and see what they say the difference is.

 

[MrTris]

Call Summit and give them the 2 numbers and see what they say the difference is.

Uh, I'm a Centennial -- do what, now?