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Discussion Starter · #1 ·
I have a 03 TJ Rubi and I’m thinking of installing the Yukon free spin kit. I know the kit will not provide a ROI to cover the cost of the kit for years on fuel savings alone. But does anyone here run one and have accurate data on MPG increase?
 

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2004 TJ Rubicon
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ROI is return on investment. OP - I would venture to say you're probably more likely to recoup costs from less maintenance on the front driveshaft over time (less rebuilds/overhauls of the u-joints and CV joint), but I have no hard data to prove that... only "angry sparrows" that appear every few years and need quieted down.
 
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I have them on the Dodge and by default the JKU with 60s. Not sure I really noticed that much gain from locking hubs.

on the TJ as I recall, you also change bolt pattern so costs go up with new wheels needed...

IMHO, any drivetrain changes to the front axle should be saved up for a 60, or at least a late model 44. Heck, rear axle as well.

YMMV
 

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My 2 cents:
I just put them on last year. They make two types: I did the hubs where the lug pattern went to 5 x 5. So had to get new wheels...therefore had to get new rear rotors, pull the rear shafts and change the pattern on those too. I also added the big brake kit to help with stopping. And since the front was apart, replaced the ball joints. Then added the heavy-duty steering link. Refreshed the steering dampener.

Did I know in advance over reading extensively on ROF and other websites that there would be no gas mileage, wear and tear on the front shaft, or any other economically noticeable benefit other than my wallet going skinnier? YES. I will never recoup a 1 cent fuel savings...ever. BUT, did I have fun in selecting the parts for the build, talking with those who know much more than me about how to proceed, understanding the interplay of all components and the need for sequential upgrades, spending the time to work on the Jeep, enjoying my time in the garage, and other overlooked but real-to-me benefits? ABSOLUTELY. That's what I was mostly going for: concept implementation and skills practice with loud music and a few beers after each day while standing around admiring the day's work, then proving that it all worked as envisioned.

The biggest benefit would be to isolate the front from a broken shaft and still be able to make it home from the trail (please correct me if I'm wrong or know of others). I can't claim that need as my prime factor for the upgrade as my real off-roading pretty much stopped a few years ago when we moved out of California.

Enjoy!
 

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Discussion Starter · #8 ·
So no one has tracked mileage before and after to document this? I know for me that simply inflating my to 30 psi I get increased mileage.

I find it odd that there is no increase. Simply because when I coast down a hill I hardly need brakes. So I’m thinking turning the front diff and shaft eat quite a bit of power.

I could be wrong but I’m going to find out !
 

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Low range burnouts in 2wd.
 

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I’m cleaning my injectors for the first time in 18 years and 170K. The only reason I’m doing that was my injector heat shield was like oily cotton candy and I was heat soaking #3.
 

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on the math part

If gas were $5 a gallon and you got 20 MPG, then it would cost $0.25 per mile to drive.
If gas were $5 a gallon and you got 19 MPG, then it would cost $0.26 per mile to drive.

So, and extra $.01 per MPG gained in that general 20 MPG area
So, at 15 MPG the numbers are closer to $0.03 change per mile
Then at 10 MPG they are about $0.05 per mile

Hmmm, Savings, we need to account for $2K to make this about MPG gain....

If you saved $0.1 per mile, its about 20K miles you need to drive
If you saved $0.05 per mile, its about 50K miles you need to drive
If you saved $0.01 per mile, its about 200K miles you need to drive

If I did all my excel stuff correct today... But this topic has been beaten to heck on the Cummins boards for years.

so I agree with @Butter Bean, do it cause you want, not for any perceived savings.


On tracking mileage, I was kind of good at it before the cars started taking over that math problem for me. I don't think I noticed a considerable bump from the dodge conversion. Ill also say the impending unit bearing failure doom and gloom I don't think that is a big deal either. I almost converted back to unit bearings, and maybe I should next time its time to rebuild the front end. The Unit Bearings may just be cheaper than all the bearings, races and seals, they are for sure easier to replace overall.
 

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2004 AiRubicon
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I'm sure there is some kind of fuel savings with unlocking hubs. New Jeeps now have FAD (front axle disconnect) to eek out any miniscule mpg gain. On a TJ your best bet is to keep your speed down on the highway, because the faster your speed the more drag and mileage plummets.
ShoeBoxes on wheels are not very aerodynamic
:LOL:
 

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There was a period of a few weeks I drove my 03 with 35's and 4.88s around without a front driveshaft. That didn't make much of a difference that I could notice MPG wise but I didn't really do a scientific study of it either. I'd have to agree that I think most of my gas goes to push the giant brick shape of the jeep and tires through the air it has to go through :D

I could drop a bunch of weight off it though .. prolly about 700lbs if I removed the top, doors, rear steel trunk drawer and crap in it, rear spare and carrier ... and I could switch to lighter wheels than the steelies I got ... but thankfully it's not my daily driver.
 
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