T-case with VC

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VC or as Toyota calles it "controll coupler" (tuna can)
The center diff actuator is behind it. They have nothing in common, it is just holding the vc up.
This is what makles a vehicle a 4X4 " The T-Case"
This is the 'thingy' that locks the diff up to 4WD. It is connected to the actuator that slides it back to lock the t-case. It is in the front output shaft housing
#1 is in the front output shaft#3. When you lock the diff #1 slides onto #3 and locks the front shaft up with the rear shaft via the center diff #2
This is the front output shaft (top), the center diff and the rear output shaft (bottom)
Would you mind cutting a cross-section out of the VC and posting a couple of pics? We'd like to see the innards of that thing if possible.


I was going to but was unsure if the stuff in side was under pressure or not.
This is what it looks like.
#1 is the fork that moves the gears from H to N to L. Its in low range now.
#2 fork that locks the center diff ( either from shifting into low range or the switch if you have one on the dash)
#3 Viscous Coupler or controll coupler
#4 high rand gear
#5 low range gear
#6 input shaft (from tranny)
#7 rear output shaft (to the rear tires)
#8 front output shaft (to the front tires)

Great stuff! Question for you. In the 2nd post above, you indicate the VC has an activator. Are you certain of that? I'd thought the VC is simply a coupling that allows for slight differences in speed of the F/R shafts, and it accomplishes it simply with fluid friction/temp - no electrical activation.

I fixed the post, thanks
The actuator is just holding it up in the pic.
The vc is locked by heat or friction not sure.
Also, a clarification on the VC's function in our 80. Typically in an automotive center diff application, a driven shaft comes in one side (usually from the front) and a shaft the VC will drive when slippage occurs goes out the other side (usually to the rear). The key here is that without slippage, there is little (residual, or "spin loss" basically) torque sent through the VC.

On the 80, I believe at all times 50% of torque goes to the rear, and 50% to the front - there is no speed related torque splitting variation. The coupling is there to allow a bit of differential in shaft speeds for cornering in high range, but does not split or alter the torque like what we normally refer to as a viscous coupling. In low range the diff lock bypasses this slippage function. Having said that, there are full time viscous systems as I believe the original Daimler-Puch synchro system on the VW Vanagon was.

Just a note of interest, which I gleaned from the notorious Nermy (that ours is only to allow shaft speed differentials not torque split).

Hey guys I am new to the site... and I need help. I have a 95' fzj80. My truck doesn't have front and rear lockers and also doesn't have the center diff lock button. I had the truck in 4wd low range backing up a heavy trailor up a slight hill. I did'nt have any problems then and it worked fine. A few days latter I changed the front diff fluid and began to notice the problem. It fells like the center diff is still locked. The steering is real darty and at high speeds,ie 70mph, its hard to hold in the road. It also roars going down the road. I took it to a buddy thats done a good bit of 80 work and he pulled the actuator motor on top of the TC and it was still working. The Center Diff light on the dash goes off once the TC is taken out off low range. We had the front-end looked at and an alignment done... still got the problem. So next we pullled the front drive shaft out and the truck drives like a dream! What is up ??? ???
Do you have any ideas... I am guesseing something in the TC. Also when we had the actuator motor out we manually , with a screwdriver, unlocked the center diff. Please send any help... I am stuck

Hello Chuck and welcome to the 80/100 section here on ih8mud.

Sorry to hear that you're having problems with your truck. How long have you had it and what is the mileage?

You will want to get the CDL switch at some point so check out the Slee offroad site or give C-Dan a call one or the other should be able to set you up with the switch.

>> A few days latter I changed the front diff fluid and began to notice the problem. <<

Did it work OK for a few days, then you changed the diff oil, and then it began to act as though the CD was locked? What gear oil did you use in the diff? Quantity? Color and texture of the fluid that was drained?

>> It also roars going down the road. <<

Please elaborate. Is this a gear noise? Front? Center? Rear? Do you notice any abnormal heat coming from the Xfer case?

>> So next we pullled the front drive shaft out and the truck drives like a dream! <<

This eliminates the front R&P and the birfields from being the source of the roaring.


(If you don't get any suggestions then start a new thread. There are a lot of people that are ignoring this thread by now.)
Well if you were able to move the truck in Hi range then the problem is in your t-case. Basically the center diff isn't free to allow the front and rear driveshafts to rotate at different speeds and is locked/frozen. I don't know of any way to diagnose this except to pull the unit and tear it down.
A locked center diff should not cause the other bizzarre behaviour he describes should it? Darty steering, hard to hold on the road, excessive roaring?

I've locked the CD in high range for short periods and don't notice any of that.

Maybe it's hung in low range but he would definitely notice that if he's had the truck more than a few days. 70 might be hard to reach in low but there would be a lot of ROARING going on. :D

Definitely need elaboration on the roaring. Is this engine noise due to high RPMs, etc??

Having the center diff locked in high range can make the truck very darty if any of the 4 tires are not identical, and also identically worn as well as at proper pressures. Obviously this would simply come from a different rolling circumference and all 4 being locked together, and explains why it drives fine without the front shaft (there's no f/r fighting). If there's a serious tire difference, then you'd literally have roaring as the off tire was getting tortured by the other 3. Here's what I'd do immediately:

1- Drain the center diff into a large clear container with a piece of screen across the top (dent it deeply into the container to minimize splashing).

2- Lift and measure each tire's circumference as precisely as possible down the center.

So, what's with the roaring? Speed it occurs? Direction it seems to come from? Change with coasting? With acceleration? Tied to vehicle speed? Tied to RPM? Also, how familar are you with the truck - ownership length, etc?

Darty steering is a serious worry and may indicate something's about to let go - I'd take this very seriously.

B, with the center diff locked you'll get some drive line windup.

My basic conclusion to the diff lockup is that he has no center diff lock switch and when he removed the front drive shaft he could drive the vehicle. The diff has to be locked otherwise the front output flange would just spin and the truck wouldn't move.

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