Driving my father-in-law's Toyota 4Runner and I put it in Hi4 because I thought, "Why on earth would you ever drive in 2WD when you've paid for a 4WD vehicle?" You're just wasting MPGs with a disabled and heavy transfer case. Then I noticed something — binding at slow speed turns, as well as other strange issues. I've heard of this issue with various part-time 4WD Toyotas that friends have — they can't actually drive them in 4WD all the time without problems.

Are you not just connecting the transfer case in one of these part-time 4WD vehicles? And why can't the transfer case handle slow turns? It's not like they're locking a center differential — are they? What am I missing here? Andrew St. Pierre White at 4x4overland makes many strong cases for always driving in 4WD, both because there's no measurable difference in fuel economy (he's tested this extensively on long overlanding trips, with 4WD engaged vs disengaged) and you gain immensely in traction control and safety. I'm confused as to the difference between our full-time 4WD and a Toyota's 4WD when activated. Somebody please enlighten me!

 

As far as I understand it, a part time 4x4 does not have a differential in the transfer case so when the hubs are locked and the front wheels are driven the system wants them to spin at the same speed as the rear wheels. When you turn, the front wheels spin faster than the rears which is why they feel like they're skipping / binding. It's pretty hard on parts. For this reason, a part time 4x4 really shouldn't be run in 4x4 when there's good traction. The Disco is full time 4x4 so it has a differential in the transfer case allowing for different wheel speed front to rear.

 

The open differential in our Discos allows the varying speed transfer front to back, and these part-time 4x4's don't have an open center differential then?

 

The big difference is that our Discos have a central differential and part-time 4x4s have a transfer case. They aren't the same. The transfer case's job is to send power to both the front and rear wheels when engaged. Some are chain driven, others use gears. When engaged, the transfer case doesn't allow for differing wheel speed front-to-rear when the wheels have traction. If it's not a locking transfer case it will let the front wheels spin if the rears have traction and the front doesn't, and vice versa because power goes down the path of least resistance. However, it won't allow either end to spin faster than the other when all wheels have traction.

I knew a guy that had an old suburban and the previous owner had swapped the rear axle in the past and he didn't know. He found out because he put it in 4x4 and it sounded like the transfer case was going to explode - it was making this awful "clink-crack" sound. It turned out that it had 4:10s in the rear and 3:73s in the front. Since the transfer case doesn't allow for different wheel speeds front to rear it sounded like it was going to explode. There's a show called Dirt Every Day where they had this happen as well. It was a square body Chevy that they took on the Rubicon. If you want to hear what an angry transfer case sounds like, that's a good episode. It's season 7 episode 11. They find that the front and rear have different gear ratios on season 9 episode 13.

 

Hopefully this helps show the difference. I got this image from https://www.mri-auto-diagnostics.com...-differential/

 

Part time 4x4 come with a central differential too. I owned a Mitsubishi Montero and it came with a 4WD selector as well as CDL and even a rear diff lock from factory. 2WD gained slightly better fuel economy. When in 4WD the noise from the drive train was higher than in 2WD. Driving in 4WD had no advantage in handling in the city and on highway/freeway.

 

You are correct, some of them do. I shouldn't have made such a blanket statement. I should have said the ones that bind are the ones without a differential.

 

Montero/Pajero is the only one I know of that does this. Brilliant 4WD system Mitsubishi came up with for those - far better than the mediocre Land Rover system.
Some newer American trucks have an auto setting for 4x4 that turns the front axle on and off as necessary. It's pretty failure prone and nowhere near as good.

Part-time 4WD (conventional, like old pickups or Toyotas) have no center diff, so it'll bind up in corners. It's also more efficient in 2wd - there's no need to put it in 4wd unless you're off road or in snow. Think of it like your Disco with the center diff locked.

 

I didn't know that. Now I have a good point, when my wife asks again why we don't buy a Tacoma. Driving on snow in 4WD sounds more dangerous without a center diff. And you have to switch back and forth between 2WD and 4WD depending on surface, because on pavement there is more wear on the tires in 4WD without a center diff. The conditions on the windy roads of the Sierra Nevada in winter can be changing with every mile because of elevation change and sun exposure. With the Land Rover I just zoom through.

 

The Land Rover system is great if you want to sit back and not have to deal with any controls. The Tacoma's system is more capable though, comparing stock for stock (unless you have an 04 with the center locker). No center diff in the snow means equal power distribution to each axle, giving more wheels the opportunity for grip, and preventing the one-tire-fire you sometimes get with these trucks when trying to accelerate aggressively on icy surfaces (or at weird angles off road). Better traction, but you can get sideways somewhat easily. Fun for people (like me) that enjoy those kinds of shenanigans, not so fun if you don't have much car control experience or didn't intend to slide.