Understanding Open Diffs

[hobiesbestfriend]

I read a lot about mini's and LC's owners being warned not to drive on dry pavement etc.. in 4 or with hubs locked. what I don't really understand is that if most toy's have open diffs, then what would it matter if the hubs were locked, as the axles could still turn individually of each other around the gears. I know my thinking is obviously flawed, I just can't figure out why? Can someone shed a bit of light on this. I'm just missing one pice I think for my my brain to get around this.

 

[goschbrandon]

Can't speak for locking the freewheeling hubs other than maybe a fuel economy loss, but driving in 4H or 4L locks up the center differential and forces the front and rear axles to turn at the same rate of speed. Since dry pavement yields no wheel slip, this can cause the drivetrain to "wind up" under the tension since the front and rear ends wouldn't be turning at the same rate with an open center differential. This windup is hard on driveshafts, u-joints, etc, and can cause breakage under extreme windup.

 

[2ndGenToyotaFan]

Open diffs are great for on road driving, because they allow one tire on an axle to turn faster (when going around a turn).

What you are hearing warnings about is driving with the front hubs locked and the transfer case in 4 wheel drive, because the front and rear wheels take different paths durring turns. The front wheels travel much farther in a turn, and the difference between the front and rear axle causes binding in the t-case.

Here's a good link, it's about the 80 series land cruisers. Our trucks work the same, but there is no center diff in the truck/4Runner t-case.

http://www.safari4x4.com.au/80scool/george_couyant/diffs/diffs.html

 

[2ndGenToyotaFan]

There is no center diff in the truck/4Runner transfer case.

Just so we're clear on this. That's why it's a part time 4WD system.

It is ok to drive with the front hubs locked with the T-case in 2wd, or with the t-case in 4wd if one or both front hubs are unlocked.

Do not shift into 4wd while moving, unless BOTH front hubs are locked!

 

[goschbrandon]

There is no center diff in the truck/4Runner transfer case.

Just so we're clear on this.

Good catch- after getting an 80 my thinking has been muddled a bit...

 

[hobiesbestfriend]

There is no center diff in the truck/4Runner transfer case.

Just so we're clear on this. That's why it's a part time 4WD system.

It is ok to drive with the front hubs locked with the T-case in 2wd, or with the t-case in 4wd if one or both front hubs are unlocked.

Do not shift into 4wd while moving, unless BOTH front hubs are locked!

I understand all this and am familiar with the concept of PT 4WD, and open diffs etc... I also get that it's ok to drive with hubs locked(again openb diffs) etc... I just don't get the corelation between the hubs and the T-Case. Seems the Hubs really don't matter (other than wear and tear), but it's really only the T-case that poses a problem, between the front wheel speed and the rear, correct? Therefore, it's really not ok to drive in 4wd regardless of whether the hubs are locked or not, is that right?

 

[Symon623]

I understand all this and am familiar with the concept of PT 4WD, and open diffs etc... I also get that it's ok to drive with hubs locked(again openb diffs) etc... I just don't get the corelation between the hubs and the T-Case. Seems the Hubs really don't matter (other than wear and tear), but it's really only the T-case that poses a problem, between the front wheel speed and the rear, correct? Therefore, it's really not ok to drive in 4wd regardless of whether the hubs are locked or not, is that right?

Incorrect, in some of the older Toyota manuals thay actually suggested you drive the rig occasionallly with the transfercase in 4-hi to get oil in the front diff and teh grease in the birfs moving and warmed up to keep the moisture out of them. Or you can drive it all you want with the hubs in and the T/C out (2-hi) and not hurt anything except MPG. When I lived in Washington, occasionally it would snow and I would drive around my 84 truck with the hubs in for weeks, this enabled me to have "shift on the fly" as long as I wasn't in a turn or spinning on some ice.

When you drive a part time rig in 4-hi on good traction surfaces then you create a "bind" in the drivetrain cos all 4 tires will be turning on a different radius, now the open diffs allow the front or rear to "split" between teh left and right tires but the t/c will bind between the front a rear tires, this is why the full time 4wd/AWD rigs have the viscous coupler in the t/c and the "center diff lock" button on the dash to make it like a part time t/c.

 

[tntoyota]

Incorrect, not all have viscous couplers L.C 93-97 do, 91-92 do not.
The diffloc switch is L.C 91-92,
but not the 93-97, only if modified to do so as is part of the wiring harness like the clock in mini's (non std. of course)

HaHa............. I know what you are saying I just think it's funny when people jump all over some body because they left something out or something that doesent even matter.

I dispatched an Email that I think will help I'll try to find it and post.

How center diffs work......newbie here FJ80 soon

--------------------------------------------------------------------------------

Ok, I'm not gonna read this whole thing

I am soon to get a 91 LC 80, I know traction already.
(I think?)

My question, If you can remove the VC can it be installed into non VC T.C?

Is'nt a T.C like a Diff, i.e

Non VC (open) center diff betwean frt. & rear axle looking to slip, dividing power evenly/ until slipage/ loss of traction

VC (ltd. slip) enguaging axle at instent slip/loss of traction


VC/non (locked) like enguaging 4WD in non AWD T.Cs?

P.S. How are those Defender boys doin it?
Is'nt that like having a TruTrac in the T.C? (My theory)
If you know.......
THX, tntoyota

 

[2ndGenToyotaFan]

Uhmmmm Are you asking questions about your 80 T-case? Try in the 80 section....

And he didn't say Land Cruiser, he just said full time 4wheel drive/All wheel drive..... FWIW......

Here's a great annimation of how an open diff works:

http://auto.howstuffworks.com/differential2.htm

Maybe try imagining the t-case as a diff where the ring gear is driving one axle shaft (rear drive shaft). When you shift into 4 wheel drive the "diff" locks in with the other axle shaft (front drive shaft) and they both turn together with no slipping or rpm difference between the 2.

In a t-case with a center diff or viscous coupling, the front and rear drive shafts can both be engauged while on a dry hard surface (road) because the diff or VC will allow for differences in rpm between front and rear.... and the front and rear diffs allow for differences between left and right and you dont' get any binding in the drive train.

The trucks/4Runners do not have center diffs or VC's.

Any more questions?

 

[Symon623]

I was just using the t/c as a comparison to a differential, or a swtchable locking differential. Not jumping anyones case just lettin them know it's OK to drive in 4 with the hubs out or with the hubs in a t/c out is all.

 

[hobiesbestfriend]

Incorrect, in some of the older Toyota manuals thay actually suggested you drive the rig occasionallly with the transfercase in 4-hi to get oil in the front diff and teh grease in the birfs moving and warmed up to keep the moisture out of them. Or you can drive it all you want with the hubs in and the T/C out (2-hi) and not hurt anything except MPG.
When you drive a part time rig in 4-hi on good traction surfaces then you create a "bind" in the drivetrain cos all 4 tires will be turning on a different radius, now the open diffs allow the front or rear to "split" between teh left and right tires but the t/c will bind between the front a rear tires,

I was just using the t/c as a comparison to a differential, or a swtchable locking differential. Not jumping anyones case just lettin them know it's OK to drive in 4 with the hubs out or with the hubs in a t/c out is all.

Seems this is exactly what I said earlier on, not sure what you are trying to correct? If they do recommend that in the earlier manuals, then they also must recommend to do it on wet or loose ground, correct? The "bind" in the t-case is exactly what i was talking about before also. And, I really hope you're NOT telling people it's OK to drive in 4 with the hubs in on dry ground.

For future posters, I understand all this, I had just forgotten that the open diffs would only solve the side to side variations between wheels and not the fact that the driveshafts are effectively locked together.

I suppose you could drive in 4 with the hubs locked, just make sure to go flying around every corner to get the inside wheels off the ground!!

 

[Symon623]

Therefore, it's really not ok to drive in 4wd regardless of whether the hubs are locked or not, is that right?

Seems this is exactly what I said earlier on, not sure what you are trying to correct?

This is what i was trying to correct in teh first quote.....I'm glad you got it figured out before any damage took place. I like the plan of getting the inside tires off the ground while cornering.....Have to try it.

In the end NO you should not drive in 4wd with the hubs in on dry pavement. If either the hubs or the T/C is out then you'll be OK. But NOT both in.

Sorry for the confusion.

 

[hobiesbestfriend]

Never an issue. I'd rather ask a thousand "dumb" questions than do one "dumb" thing and ruin something. Plus I usually keep it in 2 hi until I can't make something, then I shift into 4. So little to no chance of me trying to lock it all up on dry ground. Thanks for the info all.