Installed 4.88’s on 40’s Diesel

[susee80]

I’ve been running 40’s for about 5k now and just had 4.88’s installed. My first impression, MEH. I never felt that the diesel was underpowered with the 3.73’s what I didn’t like was rarely seeing 7th and never seeing 8th gear. So I pulled the trigger on the gears, I’ve only got a few miles on it so far so this is just an initial opinion. I’ve set the Tazer to 4.88s and I would say the trans is still working itself out. The in town mileage is already creeping up and it will hit 3rd before your across the intersection. I can definitely tell it’s significantly lower geared but I’m not convinced it made a huge difference with off the line performance. My main concern was the additional stress on the drivetrain with the large tires and I do feel this will be great in the long term. Just my two cents.

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[3VOLVE]

Any updates or further impressions?

 

[susee80]

Any updates or further impressions?

No issues at all, about 5k miles. If I were to do it over I’d go 4.56. 4.88 just feel a little low. Average about 19 mpg combined.

 

[Mbryson]

I'm kicking around rolling to 4.56 with the 37" tires on my EcoDiesel. Mostly for hill climbing ability while towing. I have NO issues with the truck as it is with the 3.73 gears and the 37" tires. See 8th gear a lot. Throw 5000-5500 lbs behind me and hit a hill, I think some gears would be good

 

[susee80]

You won’t regret it, it’s still one of the best mods I’ve done. I spent just under 2k and it was worth it.

 

[Steven_B]

I'm kicking around rolling to 4.56 with the 37" tires on my EcoDiesel. Mostly for hill climbing ability while towing. I have NO issues with the truck as it is with the 3.73 gears and the 37" tires. See 8th gear a lot. Throw 5000-5500 lbs behind me and hit a hill, I think some gears would be good

I run 4.10's with my heavy JT. If Nitro Gear was going to do another batch of their 4.30's I would have gone that route, but they weren't available when the Air Lockers and gears were going. Not even sure if they did another batch.

4.10's with 37" tires brings the RPM range for the diesel back to the stock range of a diesel Gladiator. No complaints at all.

Photos of my RPMs for reference.

 

[Larry D]

To bad nitro gear doesn't have the 4.30 gears available. I did 456s and 38s in my wife's diesel and I feel it's a little to low geared. Waiting for 4.30 gears for mine. But I do have 4.10s already on hand. I got 37s for my diesel so I might go with the 4.10s but really like to have 4.30s

 

[aevgladitorrubi]

No issues at all, about 5k miles. If I were to do it over I’d go 4.56. 4.88 just feel a little low. Average about 19 mpg combined.

Brand gears?

 

[aevgladitorrubi]

To bad nitro gear doesn't have the 4.30 gears available. I did 456s and 38s in my wife's diesel and I feel it's a little to low geared. Waiting for 4.30 gears for mine. But I do have 4.10s already on hand. I got 37s for my diesel so I might go with the 4.10s but really like to have 4.30s

You won't be happy with 4.10s

 

[Mbryson]

You won't be happy with 4.10s

I'm in the same camp. You have 3.73. 4.10 will barely be noticable. 4.30 would likely be ideal but they seem not available. 4.56 and a matched tire size is probably the way to go? (That's at least how I would spend my money)

 

[Larry D]

I'm in the same camp. You have 3.73. 4.10 will barely be noticable. 4.30 would likely be ideal but they seem not available. 4.56 and a matched tire size is probably the way to go? (That's at least how I would spend my money)

Well I got 456s in the wife's rig with 38s and not really happy with them. Can't imagine it would would be better or me being any happier with a smaller tire and 4.56's

 

[Larry D]

4.10s are a really close match with 37s to get it back to stock. Gear calculator says it should be a 4.18 Gear. I just wish nitro had the 4.30s available problem solved

 

[Larry D]

You won't be happy with 4.10s

Have you ran the 4.10s?

 

[Mbryson]

Well I got 456s in the wife's rig with 38s and not really happy with them. Can't imagine it would would be better or me being any happier with a smaller tire and 4.56's

I'm about to just go to the 4.56 and put my trail rig 39" BFG MT. As you allude to, I like to be close to stock + just a bit when considering gearing changes. Your experience causes me pause

Gearing is a VERY subjective subject. I have run 4.88 with Kevlar MTRs on an XJ. Hated it and thought I was overgeared. I made the same mistake with a 2012 JKU and went with 4.88 and 35" tires. Everyone on the interweb thought I was an idiot for not liking being overgeared. I'm the one driving it. I'm the one that paid for it. I again ran the Kevlar MTR on that rig as they ran more true to size making the overgearing slightly more palateable. I got about 7-8 mpg in the JKU driving from SLC to Vegas and back on one trip. 80-85 mph speeds. Was not that happy with it in that trip. (there is the whole flying brick aerodynamic thing to think about as well)

The JKU with the 4.88 was pretty bitchin' towing a small enclosed trailer. That was probably the only time I was truly happy with the 4.88 gears. If I did the XJ or the JKU over again, I'd go to 4.56. Trying not to make the same mistake if I were to do the JT

If I gear the EcoDeezel, it'll be to 4.56 (seems like that's what's available? 4.30 would seem ideal as you mention) and I think I'll be overgeared with the 37" tires. I'm not sure if moving from 3.73 to 4.10 is enough for me to go through the work/expense? It may be to you? I'd love to hear what you think when you do the 4.10 and 38" tires. Being in OR, I assume you'd have similar driving experiences with actual mountains that I'd have in UT.

I'm doing enough stuff through the summer that the JT is not quite enough truck for me. It's close but not quite. Nothing else even compares in the mid-size to the JT. Full size trucks do what I need them to do during the summer but the spring/fall/winter when I'm playing with the truck more than anything else, full size is bigger than I'd like it to be on the trails.

I have put 20k on the truck since buying it on Labor Day 2022. Something must be working for me. I'm kind of inclined to just leave well enough alone and steal my wife's Navigator for some of the hauling duties the JT is just barely adequate for.

 

[Larry D]

I do my own gear work so it's just parts for me and my time. I personally thought 3.73 with 33" and anything over 70 sucked fuel mileage goes down a bunch at anything past that. My thoughts is 4.10, 37s and 75 and 80 mph.

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