Viscous Coupler removal and AWD (2 Viewers)

[medtro]

FWIW, words from Toyota.

The center differential is equipped with a viscous coupling type LSD (Limited Slip Differential). In addition, a mechanism to mechanically lock the center differential when the transfer is shifted to “L” has been provided.​

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[Rich]

Rich,

There is no biasing of torque. It's 50/50 via steel gears at all times. In high range, you're running steel gears, in low range the same - steel gears. Repeat after me - this is NOT a viscous coupling.

DougM

Doug, it is a viscous coupler. It does bias torque. That is the only purpose of the VC in the 80 series Land Cruiser center diff.

In the Toyota doc above, "limited slip differential" is equivalent to saying "a differential that can partially, but not 100%, bias torque".

In the Toyota doc above "When a rotational difference is created between the front and rear wheels due to slippage, torque is transmitted by the viscous coupling from the high-speed wheels to the low-speed wheels, thus reducing the rotational difference" is equivalent to saying "The VC couples, or in other words biases torque, when the driveshafts rotate at different speeds, as would happen when the tires on one axle slip more than others, due to loss of traction."

 

[Beowulf]

If the center diff is locked then ABS is turned off by the ECU.

-B-

 

[hank14]

So, removing the VC would retain AWD under similar traction situations at all 4 wheels. Under a front or rear low traction situation with all 3 diff unlocked (for instance, the rear wheels on ice), the rear wheels would get all the torque and the front wheels would get none?

Again, this is how I believe the 98-99 100 series functions with the center and rear unlocked.

So, driving an 80 with the VC removed would not be harmful, it would only effect its ability to distributs torque front and rear in unequal traction situations.

Is this correct?

 

[RavenTai]

I honestly don't think anyone knows what it does.

I'm serious.

Curtis
91FJ80, no VC

plenty of people in this thread know exactly what the VC does, if you have been here long enough then you have been round and round abotu what the VC does on several ocations

So, removing the VC would retain AWD under similar traction situations at all 4 wheels. Under a front or rear low traction situation with all 3 diff unlocked (for instance, the rear wheels on ice), the rear wheels would get all the torque and the front wheels would get none?

Again, this is how I believe the 98-99 100 series functions with the center and rear unlocked.

So, driving an 80 with the VC removed would not be harmful, it would only effect its ability to distributs torque front and rear in unequal traction situations.

Is this correct?

that is correct,

your FZJ80 HF2AV just became an HF2A of the FJ80 and UZJ100

 

[Rich]

So, removing the VC would retain AWD under similar traction situations at all 4 wheels. Under a front or rear low traction situation with all 3 diff unlocked (for instance, the rear wheels on ice), the rear wheels would get all the torque and the front wheels would get none?...

With the VC removed, full time 4 wheel drive is retained. With the VC removed, and all three diffs unlocked, the torque distribution to all wheels will always be equal, regardless of variations in the traction at each wheel.

 

[sleeoffroad]

The easiest way to think of it, as has been mentioned before is that it is a limited slip locker for the center diff. You have three systems in parallel, open diff using spider gears, electric central locker and then the VC coupler.

With the VC coupler removed the transfercase is still AWD, but with a complete open diff. Just like a open axle differential. The central diff lock is used just like an axle locker and ensures a 100% lockup and 50/50 power split between front and rear.

 

[Beowulf]

Christo,
What are the real world benefits of removing the VC from the transfercase?
-B-

 

[landtank]

With the VC removed, full time 4 wheel drive is retained. With the VC removed, and all three diffs unlocked, the torque distribution to all wheels will always be equal, regardless of variations in the traction at each wheel.

I was going to mention this before. I also used torque to describe what I was refering to and it would seem that it is the wrong terminology. I think the term "drive" or "power" might be more accurate and could satisfy those nit pickers out there.

To me it seems you get the jest of it.

Removing the VC could only have a single benefit from what I can see and that is Fuel economy. And that would only be when the VC is "working" which would cause some drive line wind up, although minimal.

 

[Beowulf]

Removing the VC could only have a single benefit from what I can see and that is Fuel economy. And that would only be when the VC is "working" which would cause some drive line wind up, although minimal.

I'm having trouble seeing how removing the VC would improve fuel economy. When the VC is "working", there will be heat (energy) lost as the F/R bias is being changed by the VC. This translates to more fuel usage, correct?

With no VC, there is no F/R bias changing going on, therefore no heat (energy) loss, therefore improved fuel economy... correct?

If the above is correct, then can anyone explain how this would be translated to measurable fuel savings?

-B-

 

[Rookie2]

I'm having trouble seeing how removing the VC would improve fuel economy.

-B-

I think the theory here is that under normal driving conditions the discs of the VC coupling are rotating through a fairly thick fluid. It takes more energy for those parts to move through that fluid, than if the fluid or parts themselves were not there. I'd be suprized if it made much difference, but in theory it would make some. Having said that, when my front axle seals blew and my pumpkin was full of birf soup, I notice a significant (to me) decrease (maybe 10 to 15%) in fuel mileage.


Rookie2

 

[Waggoner5]

I agree. I don't see the removal as being a fuel economy booster. Now add the front hubs and the 2wd kit, since you are in there anyway, and in theory, one should get better MPG.

 

[sleeoffroad]

Christo,
What are the real world benefits of removing the VC from the transfercase?
-B-

Save you money when it is locked up Actually my theory is that Toyota put it in to get rid of some of the clunk in the driveline.

 

[Grench]

Snow?

Save you money when it is locked up Actually my theory is that Toyota put it in to get rid of some of the clunk in the driveline.

A very high possibility.

Wouldn't this style of VC show the greatest practical benefit on snowy roads? In the constant high/low traction scenario in starting up on patchy surfaces it should work well. Unlike a Detroit locker it should engage relatively gradually.

These trucks predate the onset of active braking systems for traction control. If you have ever driven an older GM 4x4 (Blazer, etc...) on snow, you get a whole new dimension on the lyric, "One foot on the brake, and one on the gas." I don't think I've ever had to use that trick with my '96, but I did have to do it once on a real slop mud road in the '92. The presence of the VC could explain the better manners of the '96.

In normal daily driving or for those of you who only see snow when you're already locked... maybe not so much.

You would have to have a rear wheel spinning to 'engage' the VC substantially and move power to the front wheels. If you're crawling over stuff, thats what the lockers are for.

The more I learn about these trucks, the more I think... Cool design!
The more I work on these trucks, the more I think... WTF is that and what does it do?

 

[70sguy]

I'm having trouble seeing how removing the VC would improve fuel economy. When the VC is "working", there will be heat (energy) lost as the F/R bias is being changed by the VC. This translates to more fuel usage, correct?

With no VC, there is no F/R bias changing going on, therefore no heat (energy) loss, therefore improved fuel economy... correct?

If the above is correct, then can anyone explain how this would be translated to measurable fuel savings?

-B-

I think the only scenario you are going to realize any fuel savings is if you like to drive your 80 in figure 8s all day or used your 80 for some sort of parking lot shuttle service.

Christo's explaination is dead on.

Some first hand experience.. I swapped my 93 to a JDM HF2A (NON Viscous)along with the 1HD-T/A442F and noticed that the vehicle felt more nimble and lighter steering in parking lot situations. Like you can just coast through a tight turn into a parking stall. I quite like it. In slick/snow situations you can bust the back end loose almost like a 2wd, best to lock up the center.
I really want to try a VC 80 again just for a subjective comparison.

As far as some sort of connection to ABS, the jury is still out on that one.
It so far has not effected the function of my ABS in any way....research continues.

 

[landtank]

I'm having trouble seeing how removing the VC would improve fuel economy. When the VC is "working", there will be heat (energy) lost as the F/R bias is being changed by the VC. This translates to more fuel usage, correct?

With no VC, there is no F/R bias changing going on, therefore no heat (energy) loss, therefore improved fuel economy... correct?

If the above is correct, then can anyone explain how this would be translated to measurable fuel savings?

-B-

OK, when driving down the road in a straight line there is no speed difference between the front and rear drive shafts so the VC (for lack of a better word) is idle. Now when driving down the road and making a turn, however small, the front and rear drive shafts are rotating at different speeds and the VC is working and causing some binding between the two drive shafts. Over coming this binding costs fuel. Now I never said you would notice it or could measure it and that it's a reason to yank the thing.

I personally think it's there for the ABS system. Even though we have sensors at every wheel the rear axle is controlled as a single unit. So if you were to lock up one of the rear tires both would be affected by the ABS system.

So in a heavy stopping situation when the truck is nose down the VC will help avoid an early locking situation so that the rear brakes stay "on" for an extended period of time avoiding early ABS activation.

 

[Tools R Us]

I doubt your going to see any mileage improvement by removing it. It has relatively little drag when idle and takes a bunch of difference in speed between the shafts before it comes into play. Remove one drive shaft and turn the flange, it can be easily turned by hand and you won't be able to turn it enough to make it develop significant drag.

When I had the CDL actuator issues, wound up running two trails with the CDL unlocked. On steep hill climbs when one wheel lost traction the truck would roll slightly back, by applying more skinny peddle it would smoothly move forward. The more power applied, the more active it becomes.

Hit the trail, turn off the CDL button, climb some hills and you will soon see how it operates. It requires significant shaft speed differences (wheel spin) before any torque is delivered. Normal driving, turning, etc. is not going to activate it.

http://webpages.charter.net/raventai/HF2AV TRANSFER.pdf

 

[Rich]

With the VC removed, full time 4 wheel drive is retained. With the VC removed, and all three diffs unlocked, the torque distribution to all wheels will always be equal, regardless of variations in the traction at each wheel.

I was going to mention this before. I also used torque to describe what I was refering to and it would seem that it is the wrong terminology. I think the term "drive" or "power" might be more accurate and could satisfy those nit pickers out there.
....

In writing that I was taking care to be precisely correct. Open diffs by design distribute torque equally. I think one can state that drive is synonymous with torque. Power, however is not same as torque, and an open diff distributes power equally only when all wheels are all rotating at the same speed.

 

[Rich]

I'd suggest that Toyota installed the VC for the straight forward purpose of improving the ability of the truck to handle lower traction situations without requiring any technical knowledge on the part of the driver regarding engaging lockers or shifting into low range.

I don't see any reason to remove the VC, other than if it has failed and permanently locked up, and one chooses not to spend the money to replace it.

 

[landtank]

In writing that I was taking care to be precisely correct. Open diffs by design distribute torque equally. I think one can state that drive is synonymous with torque. Power, however is not same as torque, and an open diff distributes power equally only when all wheels are all rotating at the same speed.

Then power it is