Viscous Coupler removal and AWD

hank14

 
Joined
Nov 26, 2004
Messages
2,451
Location
Texas
Does removing the viscous coupler from the transfer case make an 80 2WD until the center differential is locked? I am asking because of this thread and would appreciate any info, or a link to a thread. I couldn't find a clear answer using the search.

https://forum.ih8mud.com/showthread.php?t=100504

My assumption was that without the VC, the vehicle was still AWD, but had the equivalent of 3 open diffs like the 100 series.
 

-Spike-

 
Joined
May 26, 2005
Messages
7,235
Location
Phoenix
I don't have a real answer for you, as I've never been into the T-case, but if all he did was remove the v-coupler then it must act like a normal diff or he'd have to lock the CDL to move it. I didn't see locking hubs, so he's not doing that.

-Spike
 
Joined
Nov 16, 2003
Messages
6,048
Location
Dixie co. Florida
you are correct witout the VC you have 3 open but lockable diffs, unless he has done some other work that he did not tell us about it is sitll in 4 wheel drive
 

Beowulf

 
 
Joined
Mar 27, 2003
Messages
12,524
Location
Somewhere in the foothills...
hank14 said:
My assumption was that without the VC, the vehicle was still AWD, but had the equivalent of 3 open diffs like the 100 series.
I believe the ABS will be inactive or will not work properly without the VC. I cannot remember why, but the VC was an integral part of the ABS system and I realize they are not directly connected.

If it were me, I would ask him to have the VC reinstalled before buying the truck. He admits that it gained little as far as an improved MPG.... (and I'll bet a case of Boddington's that it didn't gain the 1/2 MPG that he says.)

-B-
 
Last edited:

IdahoDoug

 
 
Joined
Aug 9, 2003
Messages
8,868
The VC is not an AWD viscous coupler as you seem to be implying. It does not transfer torque from the rear wheels to the front, or vice versa as a typical VC does - they operate full time in that capacity. On the 80 it is much more a device that allows for a bit of slippage for turning.

Any stock 80 has three open diffs, with the center lockable. The 93+ models offer F/R lockablel discs as well, and a 1 hour mod allows the owner full manual control of the diffs.

DougM
 

medtro

 
 
Joined
May 31, 2003
Messages
7,262
IdahoDoug said:
The VC is not an AWD viscous coupler as you seem to be implying. It does not transfer torque from the rear wheels to the front, or vice versa as a typical VC does - they operate full time in that capacity. On the 80 it is much more a device that allows for a bit of slippage for turning.

Any stock 80 has three open diffs, with the center lockable. The 93+ models offer F/R lockablel discs as well, and a 1 hour mod allows the owner full manual control of the diffs.

DougM
If stock 80 has three open diffs, why does it need such a device to allow slippage for turning? What is locking up?
 
Joined
Jun 16, 2003
Messages
1,805
The viscous couple biases torque between front and rear axles when the front and rear drive shafts rotate at different speeds. Its purpose is to to provide additional torque to the axle with better traction.

Without the VC, the unlocked center diff would always equally split torque between front and rear axles.

The VC can be thought of as a semi locker for dummies. It is automatic in operation, and requires no action be taken on the part of the driver in order for it to activate.
 

IdahoDoug

 
 
Joined
Aug 9, 2003
Messages
8,868
Medtro,

The speed of the F/R driveshafts must be slightly different in a turn. The speed of each shaft is determined by the distance traveled by the average of the two tires on each axle. If you drove in a circle through a puddle of water, you'd find 4 separate tire tracks, with the two rears describing slightly smaller circles than the two fronts. It is this small amount of axle windup or binding that Toyota sought to eliminate on its full time 4WD beastie by installing this device so it would be easy to drive on the street, and easy on component wear by relieving pressure. It is not activated by tire slippage, for instance, such as today's typical AWD viscous couplings are - the diff gears handle that. Apparently it requires a great deal of pressure and only provides a small amount of slip.

DougM
 

hank14

 
Joined
Nov 26, 2004
Messages
2,451
Location
Texas
IdahoDoug said:
It is this small amount of axle windup or binding that Toyota sought to eliminate on its full time 4WD beastie by installing this device so it would be easy to drive on the street, and easy on component wear by relieving pressure.
DougM
So what is the effect of it being removed? Isn'y this tranny the same one in the 100 series, which does not have a VC, or did I misread that at one time?
 

CJF

 
Joined
May 31, 2005
Messages
7,205
I honestly don't think anyone knows what it does.

I'm serious.

Curtis
91FJ80, no VC
 
Joined
Jun 16, 2003
Messages
1,805
IdahoDoug said:
Medtro,

The speed of the F/R driveshafts must be slightly different in a turn...It is this small amount of axle windup or binding that Toyota sought to eliminate on its full time 4WD beastie by installing this device so it would be easy to drive on the street, and easy on component wear by relieving pressure. It is not activated by tire slippage, for instance, such as today's typical AWD viscous couplings are - the diff gears handle that...DougM
Doug, I don't follow this explanation. If the VC were omitted by Toyota, there would never be any binding in the center diff. By itself, the center diff allows the driveshafts to rotate at different speeds as wheel rate varies.

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.

With the VC installed, the "binding" that does takes place is when the VC itself "couples" biasing torque to provide more torque to the axle with better traction. Which is another way of saying the purpose of the VC itself is to bind (partially, it doesn't bias torque 100%) the drive shafts to each other, automatically, when there significant slippage between the two axles.
 

IdahoDoug

 
 
Joined
Aug 9, 2003
Messages
8,868
VC, VC, VC - get that out of your heads. Here is what a VC does. It determines torque split between the F/R output shafts of an AWD vehicle. It uses a bunch of discs with holes in them spinning in thick fluid that constantly varies the torque split - perhaps from 80/20 to 50/50. Great little device, and it generally replaces the center diffy altogether though there are a few variations.

The device in the 80 is not this device at all. In normal operation, torque is transferred by the steel gears in the 80s traditional 4WD center differential at 50/50. When cornering, this is still the case. So the gears are in conventional use. The device on the 80s center diff merely allows a small amount of rotational speed difference without varying the 50/50 torque split - a key difference.

There was a great discussion and explanation about this device by Norm on 80sCool a few years ago. Norm is one of the Cruiser Gods, and owned a well known shop in Oz.

So, it's definitely NOT a viscous coupling. Can't remember the term to describe it as it's very unusual. I'll think of it.

DougM
 
Joined
Jun 16, 2003
Messages
1,805
hank14 said:
So what is the effect of it being removed?...
The result of removing the VC is that there will not be any biasing of torque between front and rear driveshafts, unless the electric center diff locker is engaged.
 

IdahoDoug

 
 
Joined
Aug 9, 2003
Messages
8,868
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
 
Top Bottom