Gas mileage improvements?

A d30 locking hub conversion costs 900 dollars from what I can find.

900 dollars = 225 gallons of gas (assuming $4 gas which is $1 above what I pay presently.)

let's say you go from 15mpg to 17mpg (I would not expect to see this kind of improvement.) It will take you 29 thousand miles to save as much money on gas as you spent on the hubs. In the real world, where you won't gain that kind of mileage, it will take even more.

My MJ with a d30 in the front, not connected to anything (but still, even with a driveshaft on it all it's doing is spinning the disconnected front output of the TC), gets 17-19mpg. It got worse mileage before I put the d30 in because I fixed a few other things at the same time.
 
Honestly, and don't ask me why, but I HATE manual hubs. They're a PITA to work on when you have to take them apart, and I don't see a big enough advantage to having them, vice not having them. It also sucks to have to get out to lock them in, especially if it's cold outside!
 
keep0njeepin0n said:
Honestly, and don't ask me why, but I HATE manual hubs. They're a PITA to work on when you have to take them apart, and I don't see a big enough advantage to having them, vice not having them. It also sucks to have to get out to lock them in, especially if it's cold outside!
Click to expand...

amen to that brutha forgot about that fun with my ford.
 
bigalpha said:
I would think that locking hubs would work somewhat since you wouldn't be spinning any of the attached drive train when it was unlocked.

I seem to recall some people having used the locking hubs and not noticing any appreciable increase in their mileage.
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In theory, your mileage would increase with locking hubs....but I've taken 300-ish mile road trips with my front shaft disco'ed and haven't noticed any mileage improvement.......call Mythbusters.
 
XJEEPER said:
In theory, your mileage would increase with locking hubs....but I've taken 300-ish mile road trips with my front shaft disco'ed and haven't noticed any mileage improvement.......call Mythbusters.
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Disco'ing the driveshaft doesn't stop everything else in the front axle from spinning, though.
 
CherBear said:
PI used to wheel with a group of friends, one with a Ford, one with a Yota... Both had manual hubs IIRC. PITA to get out and lock them.
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Seriously? If locking your hubs is too much of a PITA, go get back on your couch and turn on some Martha Stewart show.
 
XJEEPER said:
Right.....it's as simple as this, do 2wd XJ's get better mileage than 4wd's and if so, what it the difference?
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The biggest difference would be weight. No t/case, little tube front end.

Here's another way to look at it. If there were significant gains in fuel economy with front axle disconnects, why did the factory eliminate the CAD system?

I wonder what the EPS mileage estimates were for the models equipped with the NP231 with CAD versus the models with the NP242 without CAD. IIRC, they were the same.
 
Speaking of mythbusters...

http://dsc.discovery.com/fansites/m.../dirty-car-more-efficient-than-clean-car.html

I wonder how bad a car has to be for efficiency to drop 10% that sounds like a really dirty car to me.

kastein said:
A d30 locking hub conversion costs 900 dollars from what I can find.

900 dollars = 225 gallons of gas (assuming $4 gas which is $1 above what I pay presently.)

let's say you go from 15mpg to 17mpg (I would not expect to see this kind of improvement.) It will take you 29 thousand miles to save as much money on gas as you spent on the hubs. In the real world, where you won't gain that kind of mileage, it will take even more.

My MJ with a d30 in the front, not connected to anything (but still, even with a driveshaft on it all it's doing is spinning the disconnected front output of the TC), gets 17-19mpg. It got worse mileage before I put the d30 in because I fixed a few other things at the same time.
Click to expand...


you say 30k miles like its a lot :) this is a good point though: ROI is important to think about when trying to improve efficiency of anything.
 
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I would imagine the cad system (vac disco?) was just gotten rid of because of the reliabilty issues.

however, the cad doesnt truly disconnect all that much does it? even with an open diff your still spinning all parts of the axle wouldn't you? the driver's side and outer piece of the passenger going forward, and the inner passenger side going backwards? so you've only eliminate (i think) the driveshaft from spinning. i could be very wrong on this so please correct me if i am wrong.
 
kidarkitect said:
I would imagine the cad system (vac disco?) was just gotten rid of because of the reliabilty issues.

however, the cad doesnt truly disconnect all that much does it? even with an open diff your still spinning all parts of the axle wouldn't you? the driver's side and outer piece of the passenger going forward, and the inner passenger side going backwards? so you've only eliminate (i think) the driveshaft from spinning. i could be very wrong on this so please correct me if i am wrong.
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The front driveshaft does not spin while driving a vacuum disco front end. Only the spider gears in the front diff along with the axles.

Again, what difference was there in the EPS mileage estimates between XJs and MJs that were produced in the same year, some equipped with CAD and some not depending on which transfer case was used?
 
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