Really hard to turn in 4hi

Won’t argue that! My first 4WD was in the 90’s... a 1980 Toyota pickup. That twin stick had my dad, my brother, and me scratching our heads. Also had manual locking hubs too. Took us a few weeks but we got it all figured out. When we first experienced the binding, we thought the thing was broken. Little did we know it was completely normal and would be the same on a truck made 40 years later.

The biggest changes are all the crazy traction control and crawl control settings (I have a 2017 manual so no Crawl Control for me). Putting my 2017 in L4 for the first time... it was like Christmas lights on my dash cluster. Never seen so many indicator lights on a vehicle before!

 

This is why the RWD Lo mod is a thing of beauty!

 

Quick attempt. Here goes nothing...

Binding does occur side to side. The open diffs in the axles cannot allow each wheel to rotate at ANY speed they want because the average of the diff output speeds MUST match the speed of the input at the carrier. Therefore, with the driveshaft speeds fixed together in 4wd the wheels across an axle can't necessarily rotate at the ideal individual speed for the path they are taking. This creates windup both across the axle and front to rear as each tire fights through the differential against the opposing tire on the axle which causes a fight at the driveshaft as well to the opposite end of the vehicle where the same may be occurring.

AWD just has another differential between the outputs to the front and rear. It may be an open diff, a limited slip, or any diff in existence. The diffs in the axles for either system can also be any diffs as well. There is nothing inherently special about AWD other than it includes a 3rd differential. AWD systems do NOT "lock" when slip is "detected". The system functions based on the operation and interaction of the 3 differentials.

AWD systems may indeed have a transfer case and they typically do. They just have a transfer case with a differential. A differential is an additional component included in the transfer case. In some cases the "transfer case" may be integrated into the gearbox, but an AWD system will have some kind of transfer mechanism to split engine output front and rear. The center differential does not completely replace all functions of a transfer case, it is in addition to.

Gearing has nothing to do with why an AWD vehicle functions differently than a 4wd vehicle. A 4wd truck is net geared to the same speed range as an AWD car when in 4HI. Also, in 4wd just one wheel is not spinning in the front and rear. The wheels on each axle receive the same torque because an open differential outputs equal torques. The problem is that the torque at each wheel is limited to what the lower grip wheel can handle. That's when you lose forward drive. But if you have traction at all 4 wheels, all 4 wheels are getting torque and being driven, not just 1.

Computers don't have a thing to do with the wheels being allowed to turn at different speeds. The differential allows that. The control systems may operate on top of the base differentials and modify torque distribution, but it's not the computer control system that allows wheels to turn at different speeds, the mechanics of the differential allow that.

 

Some 4Runners and land cruisers have awd + full time t cases. Lucky

I wonder if there are t case with high / low range and awd / full time for all combinations of drive modes possible (2x2 4 modes). Like running 4 low (reduction gears) but with out central diff locked so it’s in awd mode but also in low range. Hummmm

Edit, I forgot about 2wd modes.

ok so the t case could have rwd mode and 4 wheel drive mode. It also has high range and low range. And lastly it has the central differential which can be locked or not.


This is 2 x 2 x 2 = 6 possible drive modes. If you are in rwd mode then locking the central diff makes no difference so that’s is -1 (redundant combo) as far as possible outcomes so... 6 - 1 = 5 possible modes.

I have not even considered the possibilities of front and rear differential locker combos. Also if such a t case can be custom made , you could also have front wheel drive only mode (fwd) which compounds the possibilities even more !

3 x 2 x 2 x 2 x 2 = 44 modes ? (minus the redundant or meaningless combos)

 

Land Rovers and Range Rovers have been able to do that for 30+ years.

 

No, just away for a second and wow, exploded! Hahahaha. Thanks for all the info!

 

The VF4 has all those functions I believe. 2wd, 4HI with center diff, 4HI center diff locked, 4LO with center diff, 4LO center diff locked. I also think some versions used an open center diff and a later model used a Torsen Type-C center diff. I'm not sure I'm remembering this exactly correct but there is a good thread around here somewhere that covers it and some guys were attempting a swap.

Edit: Found it. https://www.tacomaworld.com/threads/transfer-case-swap-multi-mode-2wd-awd-vf3am-vf4am.627123/

 

Here's a neat video that would explain binding through understanding differentials. It's from 1937 but the visuals used can easily help the OP understand why wheels would bind.
Did i mention it's a neat and interesting video?

 

The new way, break it from misuse, then try to figure it out how it works.

 

Excellent visual, thanks for posting that

 

Simple answer the outer wheel turns faster than the inner one on a turn so in 4WD it tries to turn the inner one at the same speed and it ain't going to happen. Stop backup with the wheels straight take it out of 4WD and don't do it again.

 

My 4runner can do that. Standard drive mode is 4HI Center diff unlocked. I can also:
Lock center diff in 4HI (acts essentially as taco 4wd)
Shift to 4LO, center diff unlocked (low range gearing, but no binding)
Lock center diff in 4LO

It'd be cool to have 2WD available too but no big deal

 

Isn't that a great find?
And explained so perfectly.

 

I have abetter understand img about whatbindid wrong. Thanks for all the help. I guess a little more read of the manual on my end would have been a good start.
Thanks to those who were sincere in their help.

 

These days I'm only in 4wd when it's snowy or icy, basically when I need it. If I know I'm going to be making a hard turn on dry or even wet pavement I'll preemptively switch to 2hi to make the turn. It's pretty handy that you can engage and disengage 4hi while you're moving. If you think ahead it becomes pretty seamless to do. If you don't need it, why bother putting all that extra strain on your driveline components and waste fuel?

 

Finally someone stated it correctly! My biggest pet-peeve is when people say "open differentials are one wheel drive"

 

Actually worse: Some self labeled experts calling a 4X4 .......".....well you really only have 2 wheel drive.......".....(This being a standalone stupid comment AND as an aside not even taking into account if the vehicle has lockers, factory or added)

 

Fake it 'til you make it.

 

Really grinds my gears too when people say that!