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Old 03-08-2012, 04:15 PM   #1
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Thinkin about going to 4.88

I want to get some people's opinions on how much of a difference it will be going from 3.73 to 4.88. I have 35s on it now and the way it sits now is the way I bought it so I'm used to the 35s and 3.73s and to me it pulls really good now, but I'm about to start converting it from a freakin mall crawler to an actual off road rig. So I'm wanting to regear first along with currie steering. I'm just wanting to hear from people that made the big jump from 3.73 to 4.88 cause it seems to do good on the road to me now and I don't wanna start snapping axles and driveshafts.

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Old 03-08-2012, 04:19 PM   #2
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What axles do you currently have?

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Old 03-08-2012, 04:31 PM   #3
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It's a 99 sport 4.0 manual trans so I'm pretty sure d30 front and d44 rear
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Old 03-08-2012, 04:31 PM   #4
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Please don't tell me it's a d35 ha
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Old 03-08-2012, 04:35 PM   #5
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4.88-3.73 = 1.15

1.15/3.73 = .31

31% difference. What RPM are you at in top gear and 65mph now? Multiply that by 1.31 and that's what you'll be at with 4.88's. It'll pull about 100% better and crawl a lot slower.
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Old 03-08-2012, 04:39 PM   #6
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well i have a 2.5.. 5 speed/with 35's.. i went from 4.11 to 4.88 the biggest difference is driving on road i can actually pull a hill in 4th and even get to use 5th gear from time to time..lol off road im usually in low , it does crawl better for sure
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Old 03-08-2012, 04:42 PM   #7
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Please don't tell me it's a d35 ha
Why don't you go peak under instead of guess? Seems obvious enough.
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Old 03-08-2012, 04:45 PM   #8
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I have looked at the shape of the diff covers and found a website that identifies the axles so that's why I'm pretty sure it's d30 and d44
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Old 03-08-2012, 06:28 PM   #9
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We're running 4:88s and a 5 speed in my Dads TJ and they are a little low for DD use. Off the line response is great but on the highway constantly looking for another gear 65 is around 2000 and there is not a whole lot left to go much faster. For a manual rig that still sees a lot of street use I would personally run 4:56s
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Old 03-08-2012, 06:35 PM   #10
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I have looked at the shape of the diff covers and found a website that identifies the axles so that's why I'm pretty sure it's d30 and d44
For 35" tires, 4.0L engine, and 5-speed transmission, 4.88 is the way to go. I ran that combination in my previous daily-driver TJ and it was perfect on the highway as well as offroad.

Your rear axle needs to be a Dana 44 and look like this to be up to 35" tires....
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Old 03-08-2012, 06:54 PM   #11
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Originally Posted by Irongrave View Post
We're running 4:88s and a 5 speed in my Dads TJ and they are a little low for DD use. Off the line response is great but on the highway constantly looking for another gear 65 is around 2000 and there is not a whole lot left to go much faster. For a manual rig that still sees a lot of street use I would personally run 4:56s
You're assuming the 4.0 is a higher displacement V8 that likes to run down the highway at under 2000 RPM, under the hood of an aerodynamic vehicle, with small tires.....that's not the case. At 65mph, if you've really got 35" tires, 4.88 gears and a 5 speed, you're at more like 2500 RPM, which is perfect. Less RPM's would not do you any good and a few more RPM's wouldn't hurt a thing.

Believe me....I've been DD'ing mine for the past 3 years and driving anywhere from 90 minutes to 6 hours to the trail. Hell, if I could run 5.13's I would.
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Old 03-08-2012, 07:44 PM   #12
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Originally Posted by Irongrave View Post
We're running 4:88s and a 5 speed in my Dads TJ and they are a little low for DD use. Off the line response is great but on the highway constantly looking for another gear 65 is around 2000 and there is not a whole lot left to go much faster. For a manual rig that still sees a lot of street use I would personally run 4:56s
What is running 2000 rpms at 65? Not the TJ with 4.88 gears, 5-speed, and 35" tires. I ran that combination for over 100K miles and was never looking for another gear at 65-70 mph. Don't confuse the RPMs a Jeep requires with the much lower rpms a sleek lighter weight car can get away with. If you yourself owned a TJ with 4.88 gears, 5-speed, 4.0L engine, and 35" tires, you'd understand why it's the ideal combination and you wouldn't be pushing 4.56.
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Old 03-08-2012, 07:53 PM   #13
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I have the same question with a different set up. I have a 98 4cyl with a 5 speed. 4" lift with 33's. I drive 75 miles round trip a day and 5th gear is almost useless unless im level or downhill. Would 4:56 or 4:88 gears be better. She will go offroad @ the beach and light trails but nothing crazy.
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Old 03-08-2012, 08:01 PM   #14
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I have the same question with a different set up. I have a 98 4cyl with a 5 speed. 4" lift with 33's. I drive 75 miles round trip a day and 5th gear is almost useless unless im level or downhill. Would 4:56 or 4:88 gears be better. She will go offroad @ the beach and light trails but nothing crazy.
The 2.5L requires slightly higher RPMs than the 4.0L so for 33" tires and 5-speed transmission, 4.88 is what you want for your 2.5L equipped TJ. That is the sweet spot for the 2.5L.
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Old 03-08-2012, 08:20 PM   #15
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Very good, thanks for your help. 4:88 it is.
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Old 03-08-2012, 08:41 PM   #16
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I run 4.88s with a 5 speed, 4.0L, 35s. Great on the highway, and awesome when crawling in 4LO.
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Old 03-09-2012, 02:01 PM   #17
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You'll feel a significant difference. I run 4.88s in my 8.8 with 35s.
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Old 03-09-2012, 02:19 PM   #18
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I went from 3.73's to 4.88's. 4 speed auto tranny and 35's. Wish I could of went lower, but 4.88 is all I get right now running a D30 up front.

Still, the difference is amazing. It drives and wheels like a different Jeep.
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Old 03-10-2012, 09:32 AM   #19
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You'll feel a significant difference. I run 4.88s in my 8.8 with 35s.
Just to have the torque back in the gears is amazing. I went from 3.07's with 35's to 4.88.
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Old 03-10-2012, 09:48 AM   #20
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If you are correct about having a D30 and D44 with 35" tires the 4:88s will work good as long as you don't get too heavy on the skinny pedal. With the increase in torque comes real problems with the D30. Any time it gets into a bind... especially when turning, you are waaaayy over the limits of what it was built to take. Breaking front axles might become usual and you don't want that. Take some time to see if you can't afford to upgrade the front to a D44 and then change the gears. You'll save a lot of broken axles that would have happened and paid for the D44 anyway.
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Old 03-10-2012, 10:28 AM   #21
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Without a locker, the front Dana 30 is up to 35 inch tires. With alloy 27 spline replacement axle shafts, the Dana 30 is up to being locked with 35" tires.
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Old 03-10-2012, 11:33 AM   #22
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Without a locker, the front Dana 30 is up to 35 inch tires. With alloy 27 spline replacement axle shafts, the Dana 30 is up to being locked with 35" tires.
My buddy beats hard on his locked D30 with alloy axles and 35's. (SBC 350 motor) They have gone 4 years without breaking so far. He has broke only 2 ring gears.
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Old 03-10-2012, 11:50 AM   #23
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Without a locker, the front Dana 30 is up to 35 inch tires. With alloy 27 spline replacement axle shafts, the Dana 30 is up to being locked with 35" tires.
Oh how wrong you are, Ive been wheeling my D30 hard. I dont do mud bogs, I spend little time on trails, but must of my wheeling is on rocks. I run 30 spline molly shafts with Eton E locker and very heavy (150lbs a corner) 37's with 4.56 gears. Never had one issue with my little Dana 30. The real down side of the D30 is no manual hubs and the one piece hub gets replaced about 10-12 months on my rig due to the heavy tires and the pounding it takes on the rocks. My friends XJ has 36' Iroks with stock shafts, 4.88 gears and Auburn Elect locker. He has been wheeling his for over 6 years and has only broke one outter shaft.
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Old 03-10-2012, 11:53 AM   #24
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Oh how wrong you are, Ive been wheeling my D30 hard. I dont do mud bogs, I spend little time on trails, but must of my wheeling is on rocks. I run 30 spline molly shafts with Eton E locker and very heavy (150lbs a corner) 37's with 4.56 gears. Never had one issue with my little Dana 30. The real down side of the D30 is no manual hubs and the one piece hub gets replaced about 10-12 months on my rig due to the heavy tires and the pounding it takes on the rocks. My friends XJ has 36' Iroks with stock shafts, 4.88 gears and Auburn Elect locker. He has been wheeling his for over 6 years and has only broke one outter shaft.
He's talking about where he wheels, not where you wheel. Traction breaks stuff. Personally, I wouldn't run anything over a 35" tire on any type of TJ/XJ D30, period.
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Old 03-10-2012, 12:39 PM   #25
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I run 4.88 and my heep used to be my daily driver. I run 35x12.5r15 falken rocky mountain(34") and 36x12.5r15 TSL radial(35.5"). Both can maintain 70 at what I remember was perfect RPM. I forget exactly what it was because it's been a while since I've driven my jeep. I have 4.0l/nv3550/np231. Off road it crawls nice and slow... way better than stock.
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Old 03-10-2012, 02:59 PM   #26
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We're running 4:88s and a 5 speed in my Dads TJ and they are a little low for DD use. Off the line response is great but on the highway constantly looking for another gear 65 is around 2000 and there is not a whole lot left to go much faster. For a manual rig that still sees a lot of street use I would personally run 4:56s

Right now I have a 99 with 4.10 gears, 35s, 4.0 and 5 speed. At 65 I'm right at 2000 rpm give or take a couple of hundred. The Jeep is much more comfortable (and gets better mileage) if I keep it in 4th, running around 2500 rpm.

That seems to be the engines "sweet spot" and makes for a much more enjoyable experience. Wind doesn't bother me as much, hills aren't much of an issue and I can actually pass people!
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Old 03-10-2012, 03:13 PM   #27
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Right now I have a 99 with 4.10 gears, 35s, 4.0 and 5 speed. At 65 I'm right at 2000 rpm give or take a couple of hundred. The Jeep is much more comfortable (and gets better mileage) if I keep it in 4th, running around 2500 rpm.

That seems to be the engines "sweet spot" and makes for a much more enjoyable experience. Wind doesn't bother me as much, hills aren't much of an issue and I can actually pass people!
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Old 03-13-2012, 07:36 PM   #28
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I went from 3.73's to 4.88's. 4 speed auto tranny and 35's. Wish I could of went lower, but 4.88 is all I get right now running a D30 up front.

Still, the difference is amazing. It drives and wheels like a different Jeep.
I am in the same boat with the auto trans, 35's & D30/D44 but I now have a 4.7L Stroker and the 4:88 gears are just fine on the highway with the auto trans. I travel all over the state of Florida for work in my Jeep.
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Old 03-13-2012, 07:52 PM   #29
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What is running 2000 rpms at 65? Not the TJ with 4.88 gears, 5-speed, and 35" tires. I ran that combination for over 100K miles and was never looking for another gear at 65-70 mph. Don't confuse the RPMs a Jeep requires with the much lower rpms a sleek lighter weight car can get away with. If you yourself owned a TJ with 4.88 gears, 5-speed, 4.0L engine, and 35" tires, you'd understand why it's the ideal combination and you wouldn't be pushing 4.56.

Jerry: I have this precise combination - - At 60 MPH I am hittiing 2500 rpm with my 35" tires, 4.0L and ford 8.8 with 4.88 gears.

I agree that the jeep can roll 3000 rpm all day without damage.

That said: I wish I could hit 70 at 2500 - - I like to cruise at that speed and I do not like to have the motor screaming at me.

When I get on the road with my jeep I usually hang out at 60MPH and 2500 cause it just feels better to me. I know it can hack more.

FWIW: The 4.88/35" combo does give me plenty of zip around town - - I do have a useable 5th gear. Taking off in 2nd? No sweat foot off the accelerator and no stall. Another benefit... in sand I can take off in 4HI without struggling....previously with 33's and 3.07 ratio - - I had to milk the clutch.

Yes I have the correct speedo gear. If I had it to do again...I would probably go with 4.27: But I aint changin!
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Old 03-15-2012, 07:23 PM   #30
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We're running 4:88s and a 5 speed in my Dads TJ and they are a little low for DD use. Off the line response is great but on the highway constantly looking for another gear 65 is around 2000 and there is not a whole lot left to go much faster. For a manual rig that still sees a lot of street use I would personally run 4:56s
I have 4.88 gears in my 2006 LJ with 35's and I can travel 80MPH on cruise all day without poping out of overdrive. I travel in my state for work in my Jeep.

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