Is the FJ70 full time 4WD?

[MalcolmY]

I have a 1990 FJ70 (3F, 5 speed manual) that has a transfer case label similar to the attached image.

Is this a full time 4WD? If so what's the point in having 4HI in the transfer case since the front axle is already engaged in a full time 4WD?

Thank you

 

[coldtaco]

nope, full time and High Range are two different things.

 

[roscoFJ73]

No , these are old school but better

 

[MalcolmY]

So can you guys explain please. I understand that the only thing 4Hi does is engage the front axle, but it's already engaged in a full time 4wd, right?

 

[Hugh Heifer]

Full time 4wd is sort of a misnomer in most vehicles. Full time 4wd is most often one wheel drive that senses slip, putting power to a wheel that may have traction. Like my wife's Honda CRV or even the 100 series LC where it is activated by adding brake pressure to any slipping wheel.

I do not know if a 90 FJ70 has auto locking hubs but they will not engage unless the front drive shaft turns the diff that will turn the front axles. It would appear from the diagram on the glove box it is 2 wheel drive (limited slip so really 1 wheel drive) until you engage the transfer case to H4 engaging the front diff giving power to the limited slip diff in the front (really 2 wheel drive - one in front and one in back).

What you end up with in most 4x4s is two wheel drive. One in the front and one in the rear. Unless you have some sort of locker that prevents the limited slip, locking the axles to turn at the same speed.

Basic 4x4 stuff.

 

[roscoFJ73]

So can you guys explain please. I understand that the only thing 4Hi does is engage the front axle, but it's already engaged in a full time 4wd, right?

No , its in 2wd until you choose 4wd. Your landcruiser is essentially the same as a normal older style car, except you have a transfer case that can engage the front diff with 2 choices of ratios.
H2 on your shift diagram is High + 2 wd

There is lots of good videos on youtube with diagrams,cartoons etc. Its much easier to watch something than have it explained purely in words.
We have something that is descended from the early days of 4x4.

Full time 4wd has its benefits but it also has to find a way of keeping the transmission from winding up from slightly differing speeds between the front and rear diffs.
This requires some kind of mechanical trickery or viscous hub, but it always means extra heat and friction.
Our part time landcruisers dont have to contend with this. Part time transmission is generally considered more heavy duty which is why its still used in large trucks. We can limp home on either the front or rear diff. Full time systems(I may be wrong) will need towing.

 

[hoser]

Full Time 4wd requires a center differential for on-road driving. Limping home in either FWD or RWD is also an option for Full Time 4wd... granted the center differential is lockable.

 

[MalcolmY]

Full time 4wd is sort of a misnomer in most vehicles. Full time 4wd is most often one wheel drive that senses slip, putting power to a wheel that may have traction. Like my wife's Honda CRV or even the 100 series LC where it is activated by adding brake pressure to any slipping wheel.

I do not know if a 90 FJ70 has auto locking hubs but they will not engage unless the front drive shaft turns the diff that will turn the front axles. It would appear from the diagram on the glove box it is 2 wheel drive (limited slip so really 1 wheel drive) until you engage the transfer case to H4 engaging the front diff giving power to the limited slip diff in the front (really 2 wheel drive - one in front and one in back).

What you end up with in most 4x4s is two wheel drive. One in the front and one in the rear. Unless you have some sort of locker that prevents the limited slip, locking the axles to turn at the same speed.

Basic 4x4 stuff.

Thank you

How would only one wheel spin when the shaft is spinning the diff?

 

[MalcolmY]

No , its in 2wd until you choose 4wd. Your landcruiser is essentially the same as a normal older style car, except you have a transfer case that can engage the front diff with 2 choices of ratios.
H2 on your shift diagram is High + 2 wd

There is lots of good videos on youtube with diagrams,cartoons etc. Its much easier to watch something than have it explained purely in words.
We have something that is descended from the early days of 4x4.

Full time 4wd has its benefits but it also has to find a way of keeping the transmission from winding up from slightly differing speeds between the front and rear diffs.
This requires some kind of mechanical trickery or viscous hub, but it always means extra heat and friction.
Our part time landcruisers dont have to contend with this. Part time transmission is generally considered more heavy duty which is why its still used in large trucks. We can limp home on either the front or rear diff. Full time systems(I may be wrong) will need towing.

Thank you.

What added to my confusion, I should've mentioned this, is the existence of locking hubs on each front wheel/side. If the front axle/diff was only powered by H4 and L4, why do we use locking hubs instead of leaving the vehicle in H2?

I hope my question makes sense.

 

[AirheadNut]

Locking hubs are there to disengage the wheel/hub from the axle shaft, reducing wear on the bearings and seals in the front differential when the vehicle is in 2H. In order to engage 4H or 4L the front hubs must be locked.

The reason there are both 2H in the transfer case and locking hubs on the front axle is to completely disengage the front driveshaft and axles when driving in 2H.

I would also recommend going to YouTube and looking at some videos (engineering explained has a good one) that explain the different 4WD systems.

 

[coldtaco]

If you don’t understand 4wd systems then look up descriptions on YouTube like others have already suggested.

 

[Hugh Heifer]

Thank you

How would only one wheel spin when the shaft is spinning the diff?

A fun eplanation is in the movie "My Cousin Vinny."


Differentials are made to allow the outside wheel to turn faster than the inside wheel in a turn. This also causes one wheel to spin if it has nothing to grab traction on. Only a locker in the differential will prevent this. If thr traction differs significantly, one wheel will spin and the other will do nothing. In "posi-traction" this is also the case. Posi-traction works to deliver power to both wheels on an axle so long as traction does not differ significantly.

Here is an article for you:

Traction Aid: Your Guide to Lockers, Limited Slip Differentials, and Spools - TREAD Magazine