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VC. What's the real deal?
- Thread starter etantshi
- Start date
ironpanther
New member
etantshi did you read my description of viscous coupler operation in the rwd thread? barring an actual breakage inside the VC they don't ever wear or break down. The fluid does though.
Viscous couplers operate under the fact that a fluid resists differences in motion within that fluid. The degree of a resistance to differences, also known as shearing, is a fluids' viscocity. Viscous couplers use a fluid that is very resistant to shearing so it is quick to transfer rotational acceleration throughout the fluid. Think of our VCs as an enclosed tube filled with a fluid of decent viscosity with a pinwheel inside each end and the shaft of the pinwheel protruding out like an input shaft. If we spin one pinwheel the fluid within the tube will begin to spin and shortly there after will cause the other pinwheel to turn because the churning fluid forces the other pinwheel to churn in sync with it. This is disregarding the friction of the pinwheels' bearring and the fluid against the tube's walls. Now if we changed the viscocity of the liquid to something thinner, less of the turning power will be transfered to the other pinwheel because the fluid is less resistive to the shearing within itself.
The way in which our VCs fluid insures that it is very resistive to shearing and thus able to transfer high torque is two fold. One the pinwheel like devices are VERY close to each other, and two the fluid contains within it what are called long strand polymers. These are microscopic elastic like polymer chains that cause the fluid to be almost weaved together and thus very resistive to shearing.
These long strand polymers are what fail over time. Slowly they lose their eleasticity and begin to break apart becoming shorter and shorter till there are so few "long" ones left that the fluid loses much of it's original resistance to shearing thus becoming much less viscous.
This is a good thing. This means that the fluid can be replaced and much of the original ability of the VC can be realized as long as the internals never become damaged(which is hard to do, but possible, considering the fact that they are not mechanically connected).
Some people may report a feeling of the VC acting like an open connection because a mechanic or other party replaced the fluid with the incorrect fluid or really old fluid. That is solved simply by replacing again with the correct fluid. Limited Slip Differential fluid for viscous LSDs is the same fluid for the most part. Check with toyota on that one. They still use viscous LSDs in their trucks.
Viscous couplers operate under the fact that a fluid resists differences in motion within that fluid. The degree of a resistance to differences, also known as shearing, is a fluids' viscocity. Viscous couplers use a fluid that is very resistant to shearing so it is quick to transfer rotational acceleration throughout the fluid. Think of our VCs as an enclosed tube filled with a fluid of decent viscosity with a pinwheel inside each end and the shaft of the pinwheel protruding out like an input shaft. If we spin one pinwheel the fluid within the tube will begin to spin and shortly there after will cause the other pinwheel to turn because the churning fluid forces the other pinwheel to churn in sync with it. This is disregarding the friction of the pinwheels' bearring and the fluid against the tube's walls. Now if we changed the viscocity of the liquid to something thinner, less of the turning power will be transfered to the other pinwheel because the fluid is less resistive to the shearing within itself.
The way in which our VCs fluid insures that it is very resistive to shearing and thus able to transfer high torque is two fold. One the pinwheel like devices are VERY close to each other, and two the fluid contains within it what are called long strand polymers. These are microscopic elastic like polymer chains that cause the fluid to be almost weaved together and thus very resistive to shearing.
These long strand polymers are what fail over time. Slowly they lose their eleasticity and begin to break apart becoming shorter and shorter till there are so few "long" ones left that the fluid loses much of it's original resistance to shearing thus becoming much less viscous.
This is a good thing. This means that the fluid can be replaced and much of the original ability of the VC can be realized as long as the internals never become damaged(which is hard to do, but possible, considering the fact that they are not mechanically connected).
Some people may report a feeling of the VC acting like an open connection because a mechanic or other party replaced the fluid with the incorrect fluid or really old fluid. That is solved simply by replacing again with the correct fluid. Limited Slip Differential fluid for viscous LSDs is the same fluid for the most part. Check with toyota on that one. They still use viscous LSDs in their trucks.
ironpanther":3k8cturu said:etantshi did you read my description of viscous coupler operation in the rwd thread? barring an actual breakage inside the VC they don't ever wear or break down. The fluid does though.
Viscous couplers operate under the fact that a fluid resists differences in motion within that fluid. The degree of a resistance to differences, also known as shearing, is a fluids' viscocity. Viscous couplers use a fluid that is very resistant to shearing so it is quick to transfer rotational acceleration throughout the fluid. Think of our VCs as an enclosed tube filled with a fluid of decent viscosity with a pinwheel inside each end and the shaft of the pinwheel protruding out like an input shaft. If we spin one pinwheel the fluid within the tube will begin to spin and shortly there after will cause the other pinwheel to turn because the churning fluid forces the other pinwheel to churn in sync with it. This is disregarding the friction of the pinwheels' bearring and the fluid against the tube's walls. Now if we changed the viscocity of the liquid to something thinner, less of the turning power will be transfered to the other pinwheel because the fluid is less resistive to the shearing within itself.
The way in which our VCs fluid insures that it is very resistive to shearing and thus able to transfer high torque is two fold. One the pinwheel like devices are VERY close to each other, and two the fluid contains within it what are called long strand polymers. These are microscopic elastic like polymer chains that cause the fluid to be almost weaved together and thus very resistive to shearing.
These long strand polymers are what fail over time. Slowly they lose their eleasticity and begin to break apart becoming shorter and shorter till there are so few "long" ones left that the fluid loses much of it's original resistance to shearing thus becoming much less viscous.
This is a good thing. This means that the fluid can be replaced and much of the original ability of the VC can be realized as long as the internals never become damaged(which is hard to do, but possible, considering the fact that they are not mechanically connected).
Some people may report a feeling of the VC acting like an open connection because a mechanic or other party replaced the fluid with the incorrect fluid or really old fluid. That is solved simply by replacing again with the correct fluid. Limited Slip Differential fluid for viscous LSDs is the same fluid for the most part. Check with toyota on that one. They still use viscous LSDs in their trucks.
I'm fully aware of how they work, and operate thanks though. To say that they never wear down I feel is an untrue statement as I know the fluid can wear out (as you have stated). I would call this a VC failure as it no longer operates as intended.
The purpose of my question is to see when the time would be right to work on the VC. No one here has bought a new all trac. Almost all are used at this point and I'm sure no one knows fully the history of the car and all stresses put on by previous owners under different circumstances (ie running a smaller spare). That's why i would like to know if there are any sort of test procedures to see if the VC is still operating like it should, and what sort of mileage they go for before either failure or servicing should be required.
Nitro_Alltrac
New member
slicksic":2a7xszz4 said:I would like to know this too, if anyone has any usefull information they want to share..
How would go about replacing the fluid?
Is this correct: when the VC wears out, most/all of the power will be transfered to the front wheels?
I haven't looked, but does the BGB show how to replace the fluid?
alltracman78
Active member
Our viscous couplings aren't serviceable at all.
And I'm sure they don't have regular gear oil in them like most of the trucks w/LSD do in the rear.
There is no official checkout procedure that I know of, but if you take each end of the coupling [use the splines] and try to turn.
If you can spin it it's bad.
If you can't doesn't mean it's functioning perfectly, I don't know what the breakaway torque is.
And I'm sure they don't have regular gear oil in them like most of the trucks w/LSD do in the rear.
There is no official checkout procedure that I know of, but if you take each end of the coupling [use the splines] and try to turn.
If you can spin it it's bad.
If you can't doesn't mean it's functioning perfectly, I don't know what the breakaway torque is.
Hotrodhendrix
New member
Sounds like we need a right up to me...
alltracman78
Active member
Hotrodhendrix":wsmmql1u said:Sounds like we need a right up to me...
A write up of what?
so we have the regular (somewhat crappy) Viscous-Coupling differential? and not the Viscous Coupling Differential Lock?
http://www.autozine.org/technical_schoo ... _4wd_2.htm
http://www.autozine.org/technical_schoo ... _4wd_2.htm
alltracman78
Active member
With enough money, knowhow and time anything [within reason] can be done.
I'm sure it's physically possible to tear the coupling apart, rebuild, reassemble and reinstall.
Whether it's able to be reasonably done is another matter, and is it worth it.
I'm sure it's physically possible to tear the coupling apart, rebuild, reassemble and reinstall.
Whether it's able to be reasonably done is another matter, and is it worth it.
RedCelicaTRD
Moderator
Yup. THe difference in traction should help get the VC going and start locking in the power transfer.