To VC or not to VC (1 Viewer)

[Dave 2000]

I don't buy that as evidence of the VC not working. With absolutely no load on the front drive shaft, you're not actually generating much torque when making the output shaft spin. So, there's not much actual force being split to the rear in that example.



If it's weak, then why is it able to cause intermittent front-rear binding when making tight circles on gravel?

Here is a very informative discussion of the VC, with a link to the source document for those pages:

Difference between HF2A & HF2AV transfercase

If you think of the difference in rotational speed of the transfer output shaft when perhaps a front wheel is spinning versus a rear with traction it is this difference that brings the VC to activate, now remove the shaft (or put both ftont wheels on ice), the VC start to apply equal force but for a limited time, as the fluid heats/expands it will now impose as much force as possible to the rear wheels, and trust me the amount of effort applied to the wheels is minimal. That is how it works to my way of thinking, I could have it all wrong and am happy to be schooled but, I have tried moving my 80 (manual gearbox) and a customers 80 (auto) off of ramps and and they both struggled to get over the wheel stops with no front shaft fitted, if you try to drive yours without a front shaft, (and of course no CDL), you will find your 80 could not pull the skin off a rice pudding.

To answer your question about binding while turning, the rotational difference when cornering is IMO not sufficient enough to bring in the VC action, and if it did by the time it had activated you would have completed the turn. I have never experienced that so, either both of my VC's are weak/worn out or working correctly, for those who have experienced it perhaps they have a VC that is close to failure? Neither of my 80 customers (a rare beast here) have mentioned any issues manouvering in our village, i.e. narrow streets ect.

So, I am happy to leave it there until it fails, and when it does I may fit the spare or leave it out altogether, I am on the fence with this because it is supposed to help suppress transmission noise/slack front to rear, I am not sold on that idea, and given how easy it is to remove/refit I may try both and see if there is any difference in transmission noise on the tarmac but, I would never rely on it to get me out of a slippery situation.

Regards

Dave

 

[gummycarbs]

If you think of the difference in rotational speed of the transfer output shaft when perhaps a front wheel is spinning versus a rear with traction it is this difference that brings the VC to activate

But it's not about rotational speed, it's about torque. The Toyota document only talks about torque.

To answer your question about binding while turning, the rotational difference when cornering is IMO not sufficient enough to bring in the VC action, and if it did by the time it had activated you would have completed the turn. I have never experienced that so, either both of my VC's are weak/worn out or working correctly, for those who have experienced it perhaps they have a VC that is close to failure? Neither of my 80 customers (a rare beast here) have mentioned any issues manouvering in our village, i.e. narrow streets ect.

I've only experienced the binding on gravel surfaces, in extended circular driving, i.e. testing the system. I never once experienced any sort of perceptible binding on paved roads.

 

[-Spike-]

I've had several 80's, one with a bad VC. That one chirped tires when turning on marginal traction surfaces. The others are/were completely indiscernible. There are different levels of 'bad' on a VC, from binding a little to nearly fully locked all the time.

Removing the front driveshaft does in fact simulate having zero traction on the front axle, and the VC in theory should give its max effort to put power to the rear wheels. Been there, done that, the actual power transfer is extremely underwhelming. The VC takes a bit of slack out of the driveline and does very little else. If I were ever in my transfer case I'd remove it with no qualms, working or not, to avoid the possibility of it failing as it did in my wife's truck. It was annoying as hell, and stressed the driveline unnecessarily. In any situation where I am worried about lack of traction, the CDL gets locked. There is no downside to removing the VC, period. I wheel with several people who have had VCectomies and promptly forgot they ever had them, no regrets, second thoughts, etc. It's one of the few dumb things Toyota did, just for the American soccer mom market.

 

[Dave 2000]

But it's not about rotational speed, it's about torque. The Toyota document only talks about torque.



I've only experienced the binding on gravel surfaces, in extended circular driving, i.e. testing the system. I never once experienced any sort of perceptible binding on paved roads.

The VC must need to 'see' rotational differences before applying torque right, how else would it slip and generate any heat?

Your experience with binding on gravel after extended periods of time makes sense, the front shaft with its rotational speed difference to the rear would heat it up, the gravel allowing you to hear it working. My point being that the VC is being activated by the speed differences, and then the VC takes over transmitting more drive (torque) to the rear wheels, not hearing the tyres on paved surfaces is an indication of how limited the effort is applied by the VC and how long it takes to engage.

Regards

Dave

 

[Dave 2000]

...........several people who have had VCectomies

Never heard of that one.

Regards

Dave

 

[Tools R Us]

But it's not about rotational speed, it's about torque. The Toyota document only talks about torque. ...

The document that you posted,,, did you read it?

 

[CJF]

What really bothers me about this whole setup is that if I park my truck on a hill and ONE tire loses traction, the truck will roll downhill unless the parking brake is on (and works) and/or I have the CDL locked before I park.

I've been thinking about this, and what you posted is not quite correct, as long as the tranny is in park and the TC is *not* in neutral (but not necessarily locked either).

That one tire would not only need to be able to slide, it would need to be able to freely rotate in the opposite direction as the others. Very unlikely scenario. (Only thing that comes to mind is jacking up one corner of the rig while on a slope and not chocking any of the other wheels. Even then, it would stop once the wheel fell off the jack.)

Also, this (non-)issue applies equally well to any 2wd vehicle, or really to pretty much any vehicle, period.

 

[-Spike-]

I've been thinking about this, and what you posted is not quite correct, as long as the tranny is in park and the TC is *not* in neutral (but not necessarily locked either).

That one tire would not only need to be able to slide, it would need to be able to freely rotate in the opposite direction as the others. Very unlikely scenario. (Only thing that comes to mind is jacking up one corner of the rig while on a slope and not chocking any of the other wheels. Even then, it would stop once the wheel fell off the jack.)

Also, this (non-)issue applies equally well to any 2wd vehicle, or really to pretty much any vehicle, period.

If it can slide, it can rotate backwards. Never seen it happen, but I could easily imagine it on an icy hill.

Also, the transfer case gear selection is moot, the drivetrain front to rear is never separated, even in neutral. That's why you cannot tow the VC equipped models of the 80 with one axle on the ground, even with the TC and tranny in neutral, without destroying the VC.

 

[CJF]

Also, the transfer case gear selection is moot, the drivetrain front to rear is never separated, even in neutral.

My only point in bringing that up is that the drivetrain *is* separated from the tranny, so no parking brake = vehicle rolls freely with no slippage of *any* tire.

Basically reminding folks of the main parking no-no: Tranny in park (or whatever), TC in neutral, wheels not chocked.

 

[-Spike-]

My only point in bringing that up is that the drivetrain *is* separated from the tranny, so no parking brake = vehicle rolls freely with no slippage of *any* tire.

Basically reminding folks of the main parking no-no: Tranny in park (or whatever), TC in neutral, wheels not chocked.

Ah, yes, that makes sense. That would be really stupid.

 

[Dave 2000]

Interesting this talk about parking. The transmission brake on Land Rovers is a perfect example, LR supply a chock to be used on the axle not being lifted, to change a wheel for example.

Regards

Dave

 

[-Spike-]

Interesting this talk about parking. The transmission brake on Land Rovers is a perfect example, LR supply a chock to be used on the axle not being lifted, to change a wheel for example.

Regards

Dave

My mom's 1984 Datsun 200SX had a wheel chock. Many cars include, or used to include them in the jack kit. Any time you lift a driven wheel on any 2wd or all-time 4wd vehicle, you effectively negate the parking pawl (or engine brake, in the case of manual transmissions).

 

[CJF]

Any time you lift a driven wheel on any 2wd or all-time 4wd vehicle, you effectively negate the parking pawl (or engine brake, in the case of manual transmissions).

Ayup.

 

[Dave 2000]

My mom's 1984 Datsun 200SX had a wheel chock. Many cars include, or used to include them in the jack kit.

Not for the UK or most of Europe AFAIK, I only remember seeing them supplied on LR's, perhaps a litigation 'thing' on your side of the pond?

Regards

Dave

 

[gummycarbs]

The document that you posted,,, did you read it?

Did you?

 

[-Spike-]

Not for the UK or most of Europe AFAIK, I only remember seeing them supplied on LR's, perhaps a litigation 'thing' on your side of the pond?

Regards

Dave

More than likely. Americans are stupid.

 

[-Spike-]

Did you?

Your quoted document references rotational speeds about eleventy hundred times.

 

[gummycarbs]

Your quoted document references rotational speeds about eleventy hundred times.

The VC splits torque, not speed. Speed is the trigger. No torque means nothing to split.

 

[-Spike-]

The VC splits torque, not speed. Speed is the trigger. No torque means nothing to split.

Dude, it's the difference in torque, which causes a speed difference, that causes the VC to engage. The document explains that the difference in speed causes the silicone fluid to shear, which causes it to heat up, which causes it to become more resistant to shear, which transfers torque across the device, which is supposed to reduce the speed differential.

Don't you understand that removing a drive shaft is exactly the same as having zero traction? Traction at the wheel is resistance to driveline rotation. If there's no traction there's no resistance, exactly as there is no resistance if you remove the driveshaft or otherwise interrupt the driveline. This is a pretty simple concept.

 

[inkpot]

So if my VC is removed can I then tow it with one axle on the ground ?