Really? I figured spinning all the other components would really drag down fuel economy. So is it the same for say an older ranger with manual hubs and leaving them locked in which so many people say is an absolute no-no? I find it funny I ran around in my 88 Ford F-250 with the hubs locked in all winter and never had a problem. And never noticed any huge loss in fuel economy. Someone told me one time that leaving the hubs locked in caused horrible fuel economy loss spinning all the front drive train components. Who knows, all I know is its a truck its not a fuel saver LOL. I guess it may make a slight difference but at less than 1mpg I don't see why people complain about it.
Thanks for the enlightment adsm08. Makes sense now, never thought of really figuring up the difference.
As was already said, leaving the front end locked on a TTB front end is worse for it because the U-joints can't handle it as well as the CV joints do. It has a lot to do with the stresses put on U-joints when they are operated at high angles, like you get while turning, for extended periods.
I do leave my front hubs locked most of the winter and have sometimes forgotten to unlock them well into Summer. I have never had a failure from it, and myself have only noticed about .5 MPG loss from it. Doing that for almost 10 years I never had a failure. That front axle was all original when I swapped it out for the D-35, with no problems.
One of the other reasons for not leaving the front end locked in when it is not a live axle is the possibility of catastrophic failure if the transfer case should accidentally engage at high speed.
Here are some pictures of an F-550 that was retrofitted with a 700 piece transfer case because the driver left the hubs locked and accidentally pulled on the T-case shifter at 75 MPH.
I thought I had some pics of what it did to the drive shafts (can you say "pretzel"?) but I can't find them.