This is more of a personal curiosity than a problem I'm having. My 1999 Ranger 3.0 Off-Road features Ford's pulse vacuum activated 4x4 system that was common in the Ranger and Explorer of the period. The system had a reputation of being finicky and prone to failure due to vacuum leaks, etc. I've read about a modification that can be done to the OEM hubs to bypass the pulse vacuum activation, which permanently locks in the front wheels to the differential and drive shaft. One of the prior owners of my truck performed this modification to the front hubs, so my truck's front end acts like a live-axle, and only receives power when 4x4 is engaged on the dash. I confirmed this a while back while doing shock work, as rotating the wheels causes the front drive shaft to spin. Does the front end being permanently locked in have a noticeable affect on your MPG and acceleration up to speed on the highway? I've considered buying a conversion kit to release the front wheels when I know I won't need 4 wheel drive, if this does have a noticeable effect on MPG. I've also searched area junkyards to find unmodified hubs, to see if my system functions normally, but haven't had any luck.
Thanks!
It will definitely affect fuel consumption. The engine has to work harder to accelerate all that rotating mass (which takes more energy than static mass).
How much? I don't know for your specific vehicle. I would estimate that it'll be up to 3 mpg.
I ended up getting the manual hubs a week ago today and did the swap. There was a pretty significant change in my gas mileage, I usually average somewhere between 14.5 and 15.5 MPG. I unlocked them about 50 miles into a fresh tank of gas and ended up getting 17.23 MPG on the rest of the tank. I've only seen a gas mileage number higher than that one other time, after driving 5.5 hours on the highway I got a little over 18 MPG.
nice work. Hopefully the swap pays for itself over time.