4.30 vs 4.88 on an auto with 34's

-30-32 with no extra weight = 3.9
-30-32 with extra weight = 4.3
-33-34 with no extra weight = 4.3
-33-34 with extra weight = 4.88
-35 with no extra weight = 4.88
-35 with extra weight = 5.29
**if you have the ovtune, you can get away with more weight due to the better shifting/ low end power gains**



Im stuck between what would be best for performance and mileage when it comes to new gears. Currently im running stock 3.9 gears with a 6" lift, 34's and an OVtune. Truck drives great through town and below 55, but on the highway at 65+ I can't seem to find 6th. On my last 80mile trip I got about 18.5mpg driving 65 in 5th.

Here's the rpm my truck is currently trying to run at in 6th which is too low of an rpm to actually use.

Here's what I am currently able to run at in 5th down the highway.

Here's 6th with 4.3's here's 6th with 4.88's

Has anyone swapped from 3.9 to 4.3 and got pretty positive results, or is it worth the money to just go with 4.88 gears?

* *I've read through the forums and can't find any really first hand accounts on results of changing gears to 4.3**

 

Is there no 4.56 option for 3rd gen?

 

No, it seems the only aftermarket gears people are making is 4.88's

 

Everybody here with at runs 4.88’s. Search 4.88 mega thread. All the answers are there. Cant wait to put mine on for my 33’s

 

Best decision I've made. It helps with my 35's. Its a very helpful upgrade. Also good looking rig from a fellow defender.

 

@SearArtist just put 4.30’s in his truck

 

What kind of mileage are you seeing?
Thanks, and I I'll take that front bumper haha

 

haha thanks. I'd rather not talk about mileage lol... I'm in the 13s on a good day. Depending on wind and MPH i can see 8.6 to about 12

 

See I'm getting up to 19 on the highway doing 65 like an old man haha I only get 14-16 if I do like 70 or 75. I'm not trying to kill my mpg by getting the 4.88's which is why I'm looking at the 4.3's

 

I live near lots of mountains so i can't feather the throttle. I'm always on the gas. Not to mention the wind which can make my drive a lot more miserable. Seems like 4.30s would be fine but the second you upgrade you would need 488s

 

From what people are reporting is an increase in mpg. From what ive read.

 

People that buy a truck, lift it and add big wheels and tires,then make threads about gas mileage blow my mind.

Put the 4.88's on and be happy as you whip up hills and without a struggle.

 

Would recommend 4.88s, they'll help compensate a bit more.

Also, check out this link http://www.grimmjeeper.com/gears.html little bit better comparison tool so you can see the difference 4.30 vs 4.88 makes.

 

Well since you don't like saving money just send me your paycheck every month.

 

Okay, right after you go back to stock. How can you claim to care about saving money on gas after doing a 6 inch lift and putting 35's on a truck?
How can you care about saving money after spending what it costs to do all those mod's? Keeping it stock would save you thousands, imagine all the gas that could buy you!

I personally think it looks great, and I plan on doing a smaller lift with upsized tires myself. I just don't understand how someone claims they want to save money and does these things. They are literally opposites.

p.s. I think 18.5 on the highway with the set up you have is fantastic. I know the truck comes with an est. 22/21 but with all that extra weight and only losing 3-4mpg isn't bad imo.

Edit: I don't want to go back and forth, because I know I am not helping the thread and it will highj-ack the thing. And on top of that we probably won't agree in the end.

 

Reason you're not finding anything is because I don't believe anyone is making 4.3 or 4.56 for the 8.75 inch rear yet. At least not that I can find .

Plenty on here say 4 88 is fine but it's really over geared when compared to stock. 4.56 would be the best gearing to have it back to stock.

Being 34 might actually be ok at 4.88. when I was looking it was for 33s. Still might be slightly over geared but not too bad.

Plenty say 4.88 is great and more power which yes obviously it will be, you're over geared. Really though only place you'll have an issue is Highway as you'll be reving higher.

 

I'm probably one of a few people running 4.30's with an AT, if not the only person...only because @Trident904 was so kind to swap diffs with me when he got his 4.88's installed and it was cheap enough that it was a worth doing.

I'm on 285/75/16 S/T Maxx's which spec out to 32.91" - about as close to a real 33" tire as you can get.

Here are my thoughts: with the factory gearing, bigger and heavier tires, and the AT - the truck is definitely slower to accelerate and you run much lower RPMs especially in 6th gear on the highway. Since I do a lot of highway driving, and the interstates here are like a roller coaster, my truck was constantly shifting between 4-6 gear...not really a problem, and fuel mileage was still good at 17-18mpg, but it was annoying as hell.

I tried the SSP, using ETC all the time...nothing really made it "better"

Now, with the 4.30's installed the truck is far better than it was with the factory tires, in terms of acceleration and overall drive-ability. It is no longer sluggish to accelerate, and I can hold 6th gear on hills now since the RPMs are increased just enough to not really need to downshift. If the hill is steep enough it will still downshift into 5th, but rarely does it go into 4th like it did before.

IIRC 6th gear at 75mph is like 2000rpm.

IMO if I didn't do so much highway driving, I probably would have just saved up for 4.88's and an ARB front locker...but the 4.30's work perfectly for me and my situation.

You might not be so lucky to find someone with a MT willing to swap diffs with you like I did, however, you can find OEM 4.30's for sale if you search around. You still have to pay labor to get them installed.

 

Are the answers there for the 2.7 as well with the auto I haven't seen a post about the 2.7 in the 4.88 megathread unless I read past it . Would love to no as well is 4.88s for me as well with 255 85 16s . The kicker of it all is no one in my area will touch the gear swap in my area . Thanks for starting this thread op

 

Just what I was looking for. Thanks man!