johnfkellogg

I am looking for anyone with experience running 4.88 gears in general and secondarily do these gears help for towing a trailer up to 3,800 lbs loaded with gear, water, etc.

The problem I see coming for me is my 2000 xj now weighs 4,600 lbs. loaded. I already have back and forth shifting in 3rd going up miles of elevation from 2300 to 9,000ft in Arizona and surrounding states.

I currently have 4.10 gears; 33 inch All Terrain tires; 3.5 inch Rubicon Express with upper & lower control arms; ARB lockers front and rear; transmission cooler, SYE, etc.

I am considering staying where I am and getting a small pop up/expedition trailer; go up one notch to the 4:56; or go 4.88; but would like to ask before I go or stay.

Thanks
John Kellogg
Tucson, Az

XJwonders

What engine do u have?

Fred/N0AZZ

He has the 4.0.


John like I said in another thread I think the 4.88's would be your best choice for what you plan on doing as I run 4.56's with 33 and 35" tires and wish I had went with the 4.88's instead as mine is used mostly off road.


The 4.56 gear and 33" tires give you a stock setup, the 4.88 would give the gearing like in a factory tow package as such going from a 3.55 to a 3.73.


You said the mileage wasn't an issue so the 4.88 is about the only way to haul 8400# up to 9,000' and the lower gears will help when exploring the trails off road or making your own.

XJwonders

I agree on the 4.88

johnfkellogg

Thanks,


I wanted to check one more time with someone who is using 4.88 gears before I committed.


I am going with 4.88 post results later.


Order 4.88 gears (that fit Dana 30 & Chrysler 8.25 with ARB lockers).


Keep 33" tires 3.5 lift


Note: just replaced rear springs with new Rubicon Express R#1463 & gained back 2" rear lift due to sagging 10 year old RE1463's (front coils have lost 1/2' due to age/sag)


Get use to gear change and evaluate application for trailer/hills/off road. With 31's this should give me 4.56 actual - if I read chart correctly.


make decision regarding 4.5 lift with 33's which should then give me 4.10 actual or back to where I am today, correct? --- we will see.


I think that is it....appreciate your responses.




John
Tucson, AZ

nolanbalzarini

you sound like me. az life. 5000 lb xj. mountains and ****. towing trailers sometimes. 33's and 3.5" lift. i went 4.88s and i do love it. i know some people think its too low but i don't.
and also 34's or 35's might be in the future and a 4.5" lift. maybe(probably not). gears are good. get the deepest ones you can handle. and low range is low as ****
if you were in prescott i would even go as far as letting you try before you buy and drive mine around a bit.

Fred/N0AZZ

John with the 33" tires a 4.56 gear would be equal to stock gears and tire size. The 4.88's are a step above that and would equal a 35" size tire as stock or make the 33's with the 4.88's like a towing package gear in a stock size ie. 3.55 stock/towing pkg. 3.73 understand?


A 31" tire with 4.10 gears would equal stock with the 4.88's the 31's would seem like a 5.13 gear, smaller dia. I think I screwed you up somewhere sorry if I did, anyway hope this helps a little.


John when I ordered my gears Rustys had the best prices on Motive gears (I have used these in my race cars for many years in apps up to 1500+ HP with a transbrake no failures). The set for my D30.Chy 8.25 in 4.56 was under $500 with good quality master install kits. The 4.88 could be higher and not all mfg's make that ratio.

thatXJguy

From my understanding, 4.56 was a little higher than stock with 33s? Kinda like the towing package? I got this information from the grimmer Jeeper website that caluclates the best ratio. That's why so many people wanted 4.27 even though no one made that gear ratio for our axles.

Anyways, I had the choice between the two and I went 4.56, but I don't do any towing. I have 33 inch tires and I won't go any bigger. Deeper gears are probably better if you're going bigger than 33s though.

The weight and type of 33-inch tire you go with has a lot of say in what kind of torque rating you need. For example, my Cooper STT Pro tires on 15x10 steel wheels are significantly heavier than my Goodyear Wrangler Duratrac tires on 15x8 steel wheels were. So much heavier, in fact, that doing a tire rotation makes me sore the next morning now, and it never did before.

If you go with a really heavy tire/wheel combo, then the torque rating should be increased so you don't lose your power. And as XJWonders knows, I'm currently installing a heavy duty steering brace to deal with my new tires.

I guess the driving I do had a lot of say in what I chose too. I drive a lot of 50mph roads, and some of them even increase to 60 or higher. My MPGs suck right now when I go over 60mph, and I would feel bad for anyone that goes with deeper gears than me and needed to do that kind of driving on a daily basis. As far overall gas mileage goes – I didn't see a single change in my MPGs around town when going from 3:55 to 4:56 because I always drove carefully even on the 3:55s. The only difference I see is faster takeoff and better shift points, and MPGs suck worse on highways.

XJs NEED gears, don't get me wrong. I love my gears. Would I go 4:88? Not unless you need the extra power for larger tires in the future. I'm staying 33, so it made sense to stay around the factory power band for me. For heavy off-roaders, I understand that the 4:88 ring gear is also weaker?

XJwonders

that's right 4.27 is better ideal for street use on 33's. That's why I'm gonna do 4.27 on my purple jeep.

Yes that's right the pinion head on the 4.88 gear is much smaller but I don't think there would be any problem if running 33's. There's plenty of people running 4.88 on Dana 30 with 35" tires with no problems.

2000CHERO

I DD mine on 33's with 4.88. And will be making its first 9hr trip since regearing in a couple weeks. Around town it's awesome.

I agree with thatXJguy that tire size/weight plays a role. I had 33x10.5 BFG A/T's on with the 4.88 and it had plenty of power but was a little high in the rpms.

Since getting meatier 33x12.5 Goodyear MTR's it seems to be right where it needs to be. You could feel the difference from going from that thinner tire to the wider meatier. Even if you plan to stay at 33's take Fred's advice and get the 4.88's. With all my armor, and any gear/people that go into the jeep, the 4.56 would not have cut it even on 33's.

And like XJwonders said the ring and pinion are smaller, however don't be scared off by the Internet myth of broken r/p in the 30. Could it break, sure anything can. They key is proper setup, so use a very reputable shop. Also a full case locker and heavy duty diff cover help keep carrier deflection to a minimum.

nolanbalzarini

I think for a dedicated crawler 4.88 might be too deep and therefore weak, but I don't know any dedicated crawlers on a dana 30. for an exploration or dual purpose rig on 33s (like mine, and the op) I know now that I would not have been happy with 4.56. when I drove to moab I got 20 highway. I still get 12 city, but that's partially my fault. I used to always get 12, whether going up hill or falling out of an airplane.

2000CHERO

Not trying to argue with you, just playing advocate, but show me anything that proves there was a failure because it was "weaker".

I agree it there is less contact and the pinion is smaller. But 75% of failures I've seen were contributed to improper install, and the remaining 25% were a situation that would have broken even 4.56. The only thing you really need to worry about if running open carrier is deflection. Even then it's not as bad as everyone makes it out.

You want the deeper gears for a crawler, why do you think people put up to 5.38 and beyond under their axles, not a in a 30, but still deep.

We're not talking about dedicated crawlers, op asked about towing, and with his vehicle weight and what he plans to do 4.88 are really the only way to go. I was just saying he doesn't need to be worried about his 30 exploding if he does 4.88.

Fred/N0AZZ

Something is really wrong there if you saw no increase in MPG after a swap from 3.55 to 4.56 gears. The constant up/down shifting between 3rd and 4th of the trans all the time with 33" tires even on level ground should have told you something when it stopped. That eats a lot of fuel in itself not holding a steady MPH ever it seemed. My XJ is heavy and always loaded in the cargo area to boot, I increased by a min. of 5 MPG with the change. In fact that alone ended up being one of the most cost effective swaps done to my XJ, fuel savings.


I think you are the first to say you gained zero MPG's with that swap on 33's what might be the cause?

thatXJguy

I honestly think it's just because any normal person mashes the gas pedal when they have 3:55 gears and 33's to actually get going, and I was careful not to do that. So many people would pass me. Now, with my 4:56, I mash the gas pedal all day long and get the same mileage as I did being a granny with the 3:55s.

That being said, did I see an increase in gas mileage? – No. I still fill up at every 220 miles. Is the Jeep more efficient with fuel on a power/efficiency standpoint? That I'd say it is.

You are right, I no longer have downshifting issues, but that's only because I have the proper torque ratio now. MPG is all related to manifold pressure, and when you're turning higher RPM, you will be burning a higher quantity of air/fuel per minute. I know you're one to refute this claim in the past, but it only seems to make sense, to me anyways.

From what I've understood and always believed, turning those pistons with the crankshaft means your engine is going to use its vacuum to pull in a set volume of air from the intake system, and your computer needs to add a proper amount of gas so that you don't run lean or rich. By rotating faster, it just means you're creating a chemical reaction with a higher volume of air per second. It's not going to add less fuel if you're dumping a ton of air in because that'd be bad for the motor and could lead to spark knock. It's going to use more fuel if you're pulling in more air to keep the balance just right, which is essentially exactly what higher RPMs will do. I never really could wrap my mind around why gears would make a difference in fuel usage in that respect. It'd all have to be in your driving habits.

The downshifting never really occurred with the Goodyear Wrangler Duratracs. I really had to be putting 75 MPH to the road and traveling uphill for my Jeep to downshift. That was when life was good and I never really felt the need to re-gear. But man, I tell you, the Cooper Discoverer STT Pro tires I just put on mid-last year are so much heavier that my Jeep would downshift at 55 MPH on an incline, so that really changed my perspective and made me re-gear. The Jeep felt undriveable on those tires with stock gears – a true dog. Now I can maintain a good speed without that downshifting crap!

Fred/N0AZZ

Gears are a big factor that I found out many yrs ago with race cars and different track lengths from 1000', 1/8mi., 1/4mi.. I had to run different gears for each of them or the car suffered 3 different sets all Ford 9" setups so change was very easy.


I'm not an expert but people have written books on gears/tire size lol. All I ever cared about till a few yrs. ago with the Jeep was which one of my cars was running a "Big Tire" unlimited size or "Small Tire" 29" tall and 10.5 wide slicks. All you wanted was to hook at the line, 60' well and keep the engine in the max HP/Tq range through the gear ratio and shifts. If you made a bad call on those or the tune you lost and went on the trailer.


EPA mileage is given using the facts given on the door of an XJ or any car for tire size and pressure along with factory gear ratio change any of those and the mpg will also.