freewheeling hubs on Previa all-trac

Manual locking hubs (I assume that is what you mean by "freewheeling") don't make much sense on a Previa All-Trac because the center differential would still be spinning the front driveshaft and axles so there is little or no fuel savings and reduction in drivetrain wear. On a 4Runner with a transfer case, installing manual locking hubs would stop the front drivetrain from spinning.

It would save a bit because you eliminate some of the fronts road rolling resistance, but it's mostly like Ray said. If you really need to improve mileage you can drop the front prop shaft for the good weather months. I don't know if that is a possibility for you on your Previa, but I know a few that do it to larger fleet 4WD trucks.

I heard an energy analyst talking head on TV last week predicting gasoline prices at $3.75 / gallon in April, so I guess the pricier energy becomes, the more effect little things will have on your pocketbook.

The rear shaft is easy to drop, but I think the front would be problematic. I dont know though, I havent tried, I just think its harder to get at. The problem with dropping the rear shaft is that the tranny doesnt hold in Park anymore. This leads to unwanted insurance claims in parking lots. :(

The front driveshaft on the All-Trac Previa is 3 or 4 times as long as the rear driveshaft, which is about a foot long.

Removing the driveshaft is actually fairly easy, but putting it back in without causing a vibration can be more problematic if the vehicle is driven with the driveshaft removed. The trick is to mark the exact relationship between the companion flange on the front and center differentials and of the U-joints on the driveshaft. If they are put back out of phase, you may end up with a vibration, and the possible permutations when putting it back together can drive you nuts. Speaking of nuts, also mark the exact hole that the bolts came out of because weighted bolts are sometimes used to balance the shaft - put a bolt in a different hole and you may end up with a vibration.

IMO, it is not worth the effort to install manual locking hubs or remove the driveshaft on an all wheel drive vehicle. You are better off doing basic things like additional air pressure in the tires, looking for lower rolling resistance tires, keeping the engine in perfect tune with OEM ignition parts, and unloading any unnecessary weight in the vehicle like mother-in-laws ;-)

Ray, I'm just guessing that your MIL or wife are not members of this NG.

Nope!

I just learned from the archives they made a part-time 4WD version east of the Atlantic. I wonder how hard it would be to convert one? I'm sure its beyond my budget, but I sure would like to see it.

On a related note, I keep seeing people advertise front wheel drive Previas but I thought they were all either AWD or RWD in the US??

A part-time 4WD system usually uses a transfer case instead of a center differential so plan on at least $1,000 to change over to the transfer case, plus any changes in the driveshafts and control/shifter mechanism. At a savings of 1 or 2 MPG, you would have to keep the van for a loooong time to recover the expense.

Previas sold in the U.S. are either RWD or AWD. Toyota's first FWD van sold in the U.S. is the Sienna.