What Turns in a 4x4 in 2WD to Reduce Mileage?

I searched this forum and Google and couldn't find the answer...

What turns in a 4x4 Tacoma when its in 2WD that causes the mileage hit over a PreRunner? This is my first 4x4 so I don't fully understand how it works yet.

I took a look under the truck and I think that the front wheels turn the front driveaxles whenever the truck is moving? More rolling resistance? There is a boxy assembly with a large electrical connector at the transfer case and I'm guessing that is where the front driveline is engaged when the 4WD switch is turned.

How is the setup in the Tacoma different from the older 4x4s where you would have to get out and lock the hubs?

-Thanks!

 

The 4x4 consumes more gas because it carries a transfer case and front differential for extra weight. And since we don't have locking hubs, the front differential and axles are spinning all the time which consumes more fuel too. Locking hubs can be unlocked with the transfer case in 2wd and the front axles and differential stop spinning all the time.

 

Thanks guys! The Toyota website does say the curb weight of the 4x4 is 235lbs more than the PreRunner (4045 vs 3810lbs). Too bad hubs aren't available for the 2nd gen Tacomas so the front axles don't have to freewheel all the time. I'd think we'd get a little better gas mileage.

 

The pre runners are heavier than 3810 lbs. I had mine weighed with an empty tank and all the extra stuff removed. i.e spare tire, tools, etc.. and it was right around 4100 (IIRC)

 

My last trip out we were loaded at 5,600#s.

The best bet for mileage improvements is light skinny tires. In my other trucks I cannot say that hubs made as much of a difference as tires do.

 

I did a search and couldn't find anything - is it even possible to convert a 2nd gen to manual hubs?

 

If you put a solid axle under it.

SManz - you won't notice any gas mileage improvements simply by stopping the rotation of the front axle shafts. The only thing that really does is prevent wear/tear on the front axleshafts & bearings.

 

that's why i got a regular cab 4x4 with the 4cyl....best of both worlds

 

The Truck has to spin 4 wheels instead of 2. More rotational mass is probably the key cause not including the added weight and kinetic energy loss through added mechanical components.

 

Correct me if I am wrong, I believe the Tacoma hubs are always locked it is the transfer case that disconnects. Thus, the wear marks on the CV boots?

Anyway, of all my 4x4s I like the Toyota hub system the best. I use shift on the fly in the rain while on the street. If I am entering a wet corner I will shift into 4wd to go through it. That eliminates that inside wheel spinning on wet asphalt.

Being an old guy But I am listing the different setups I had in order of preference:

1. Continuously locked hubs because I use shift on the fly 4x4 on the street during slick conditions.

2. Manual locking hubs are next choice because I will lock the hubs in when I think I may have slick conditions that day, month, etc.

3. Auto locking hubs like Ford used on their 1990's pickups just sucked IMO. They never engaged unless you were moving. I got stuck on ice at a stoplight in Michigan and 4wd would not engage because the rear wheels spun and the truck would not move to engage the hubs.

 

DC's weight a lot more than the Xcabs or Reg cabs too.... just a note. They don't differentiate the MPG difference, between the cabs. just the engine and trans/drive. So according to the EPA & Toyota the reg cab vs DC long bed doesn't make a difference.... right. I'm sure theres quite a bit of extra weight. 4cyl 5spd Xcab 4x4 my friend...

 

These are not auto locking hubs, they are drive flanges. It is much similar to the Toyota's of the 90's, they have a disconnect at the front diff.

 

Correct bsfarmer. the CV is flange bolted to the front hub/wheel with no disconnect. The only real advantage of having manual hubs is if you break something, like say the front Ring & Pinion you can still drive home Ask me how I know this....

 

One thing that affects the mileage in a 4x4 is the gear ratio, taller gears for a 4x4 mean less mileage. I know on my 89 Jimmy locked verses unlocked was about 2mpg which was more than 10%, but from looking at the cost, time and effort of an aftermarket conversion its probably not worth it. Personally I think manual hubs should be standard equipment on all 4x4's and those that feel they need a 4x4 to negotiate the odd wet road or thick covering of leaves in their driveway can order the automatic ones.

 

Licking hubs are also not going to release when you need them the most like many self-locking hubs do.

 

To get more technical...and more for offroading situations.

There are more advantages to having manual hubs.
They prevent wear/tear on the front driveline components (bearings, gears, etc) by not running them constantly.

If you have a locker in the front & it's engaged - you can unlock one side (hub) at a time to help with turning, prevent breakage, gain more traction to one side....etc, etc, etc.

Besides all that... manual hubs are easier to maintain & repair when things fail.

 

Yes, you are correct... what I thought were called auto. locking hubs (from my old Jeep days with auto. locking hubs) is really called an ADD (auto. disconnecting differential) and by disconnecting one of the half axles from the differential, the differential and front drive shaft does not rotate when the front tires rotate when in 2WD.

 

Man, I do love my 1999 with manual hubs.