To VC or not to VC

[gummycarbs]

Same here. My old Wagoneer NP229 has a VC that I used a lot on steep, icy hills back in CO. I could feel it work when a wheel started spinning. I could swear I get the same sensation in the LC but don't have any empirical data.

When I was a kid, my family had an old school (1980ish) Wagoneer for awhile. My dad went in a hunting trip with friends and had to tow everyone else's rig -- including a 4x4 truck with a trailer -- up an icy hill. The Wagoneer (Quadra-Trac) was the only one that could get traction!

 

[Dave 2000]

The advantage having a VC really is minimal. The general consensus is they were fitted to reduce noise across the transmission front to rear, and enable just a little (very little) assistance to keep you moving if a wheel hit a slippery surface.

Do not confuse the 80 VC with the VC found in modern AWD vehicles, the 80 version really is a minimal device, modern systems can sustain locking and unlocking on loose surfaces, the 80 version cannot, they eventually heat up and seize.

I have two units, one from my 94 and another from a late 93, both in good condition and both act the same. With the front shaft removed, any attempt to drive (without engaging my CDL) will result in a shed load of revolutions and about 5 MPH! So, if your even vaguely on a slippery surface with little momentum the vehicle will probably stop.

Take it from someone who off roads regularly, if it is seized, bin it and fit the CDL switch, you never know you might even see your MPG go up, the bloody thing is so heavy!

Those that have one still installed, leave it until goes wrong, my present 93 version mileage is unknown but still works..........or should I say 'think'it does, the spare sitting on the garage shelf 250,000 miles ish and was working fine when it was removed.

Re the part time kit, I am on the 'nay' side of that fence so let's not rehash that again.

Regards

Dave

 

[Dave 2000]

Open center, no VC, AWD on an 80 series is still VERY sure footed on wet, gravel, slick roads etc.

Remember, 91-92's came stock that way (I have two). I've NEVER thought, "gee, I sure wish I had one of those VC things..." I doubt you'll even be able to find an instance where you notice the difference.

On the other hand, an 80 with the front DS removed, so rear drive only (like yours is now, and how one of mine currently is), does HORRIBLY on things like packed snow, etc.

It's the AWD that makes it sure-footed, not the VC.

Good to see someone who drives an AWD vehicle and appreciates the surefootedness the stock system offers.

Regards

Dave

 

[BILT4ME]

Any situation where you get one wheel spinning. The VC acts like a limited slip differential for the transfer case. You'll probably never really notice it. The only time I did was when turning tight circles on gravel, where you'll see tire slip occasionally and feel a slight lurch. I was confused by this at first, thinking it was a binding Birfield!

Jeep had a similar viscous coupling setup from 93 - 95 (NP249 Quadra-Trac). My 95 ZJ was amazing when I drove through a blizzard.

We still have our 95 ZJ. 256K on it. I changed the T-Case on it at 176K to the part- time 2WD version. It still has a VC in it, but it also has a lock for the CDL as part of it. That thing will push snow over the hood and keep digging.

I have been running the interstate with 8" of snow, cars all over the place, and I could cruise past them as if out for a Sunday drive. I pulled up next to an F150 4wd that was stuck and asked if they needed help. They said no, and told us where NOT to go, because it was too deep. So I drove over there, through the area I wasn't supposed to go, and came back and asked if that was where they were talking about.

They grumbled, looked down, and went back to digging. We laughed.

I have yet to get weather bad enough to challenge our LC. I'm looking forward to it.

 

[CJF]

Any situation where you get one wheel spinning. The VC acts like a limited slip differential for the transfer case. You'll probably never really notice it. The only time I did was when turning tight circles on gravel, where you'll see tire slip occasionally and feel a slight lurch. I was confused by this at first, thinking it was a binding Birfield!

In theory, yes.

But like you said, it's a pretty weak (rather than aggressive) slip limiter. Will not make the rig perform noticeably better on gravel, packed snow, etc. Basically, the only time you might notice a difference is a time when you'd want the center locked anyway.

 

[BILT4ME]

In theory, yes.

But like you said, it's a pretty weak (rather than aggressive) slip limiter. Will not make the rig perform noticeably better on gravel, packed snow, etc. Basically, the only time you might notice a difference is a time when you'd want the center locked anyway.

I have actually pulled my 96 front end up onto a pile of snow in a parking lot to test this theory.

As the front wheels entered the snow pile, my momentum carried me up about halfway. My rear tires were still on dry pavement.

As I accelerated, my one front tire would spin, but I would not go anymore forward unless I really got it to 3500 RPM.

As soon as I placed it in low to lock my CDL, I was able to climb up and over the pile. (I had not done the pin 7 mod yet)

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.

 

[gummycarbs]

I have two units, one from my 94 and another from a late 93, both in good condition and both act the same. With the front shaft removed, any attempt to drive (without engaging my CDL) will result in a shed load of revolutions and about 5 MPH! So, if your even vaguely on a slippery surface with little momentum the vehicle will probably stop.

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.

In theory, yes.

But like you said, it's a pretty weak (rather than aggressive) slip limiter. Will not make the rig perform noticeably better on gravel, packed snow, etc. Basically, the only time you might notice a difference is a time when you'd want the center locked anyway.

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

 

[CJF]

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

Because it isn't able to when making not-so-tight circles.

 

[baldilocks]

In theory, yes.

But like you said, it's a pretty weak (rather than aggressive) slip limiter. Will not make the rig perform noticeably better on gravel, packed snow, etc. Basically, the only time you might notice a difference is a time when you'd want the center locked anyway.

I can tell you, as a guy who runs rocky trails, that you don’t have be up against a very large rock with one tire before you realize you didn’t depress the cdl button even in low range. A tiny grade in my hood without the front drive shaft could defeat my VC.

 

[Tools R Us]

I can tell you, as a guy who runs rocky trails, that you don’t have be up against a very large rock with one tire before you realize you didn’t depress the cdl button even in low range. A tiny grade in my hood without the front drive shaft could defeat my VC.

Agree, a properly functioning VC is a weak limited slip, at best. To get to "humping" requires significant speed differential between the drive shafts, in other words wheel spin. Even then is weak, once this happens the speed differential is reduced/gone, so returns to normal, often without doing the job. They are weak, any useful action is delayed, once "on" the action is brief, pretty much useless, far better off to lock the center.

That said, at this point, how many are still "properly functioning"? Most that we work on are stiff to very stiff, the fluid past it's best by date and don't "hump". When properly functioning should be able to hand turn a driveshaft with the other stopped, most now need a pry bar. Should not bind/slip a tire in a tight turn, even on gravel, if it does, likely the VC is bad. A binding VC puts a bunch of load, wear on diffs, axles, u-joints, birf, etc, and can make CDL activation difficult.

You guessed it, at this point, our default plan to to remove them when servicing the transfer. AWD is great for traction, the VC adds very little (if anything) to it. If it was such a great thing, why was it removed on the 100 series?

 

[baldilocks]

Agree, a properly functioning VC is a weak limited slip, at best. To get to "humping" requires significant speed differential between the drive shafts, in other words wheel spin. Even then is weak, once this happens the speed differential is reduced/gone, so returns to normal, often without doing the job. They are weak, any useful action is delayed, once "on" the action is brief, pretty much useless, far better off to lock the center.

That said, at this point, how many are still "properly functioning"? Most that we work on are stiff to very stiff, the fluid past it's best by date and don't "hump". When properly functioning should be able to hand turn a driveshaft with the other stopped, most now need a pry bar. Should not bind/slip a tire in a tight turn, even on gravel, if it does, likely the VC is bad. A binding VC puts a bunch of load, wear on diffs, axles, u-joints, birf, etc, and can make CDL activation difficult.

You guessed it, at this point, our default plan to to remove them when servicing the transfer. AWD is great for traction, the VC adds very little (if anything) to it. If it was such a great thing, why was it removed on the 100 series?

Standby while I give Mr. T a jingle to ask.

 

[Lumpskie]

I did a test earlier this year that just came to mind. I flexed my rig out, no CDL. I got out and took a picture. When I got in, I could feel the rig slightly move forward in L and reverse in R. It wasn't enough to get me out of the ditch but it did slightly move the vehicle. (moved enough to kick up a little dirt but not get my tires to grab) I attributed it to the VC. Not as strong as my Wagoneer but it was still noticeable... at least in my mind it was.

 

[scottryana]

How many of these VC are operating as they were intended? If the silicon oil in the fan coupler can die, this oil is no different. So yes it might be weak now, but how was it 20-25 years ago. I like the idea of the VC and think it should be explored more but seems no one really wants to bother.

 

[Tools R Us]

Standby while I give Mr. T a jingle to ask.

Tink, tink, tink, is this thing on? Did ya git the answer yet?

 

[Tools R Us]

How many of these VC are operating as they were intended? If the silicon oil in the fan coupler can die, this oil is no different. So yes it might be weak now, but how was it 20-25 years ago. I like the idea of the VC and think it should be explored more but seems no one really wants to bother.

The fluid turns into a thick nasty paste, so doesn't work properly, just binds. Playing with them would be fun, but don't see a realistic way to do it?

 

[baldilocks]

Tink, tink, tink, is this thing on? Did ya git the answer yet?

He said the 100 didn’t get VC’s because of weight penalty imposed by the epa. That little chunk of metal weighs 12 pounds.

 

[Tools R Us]

He said the 100 didn’t get VC’s because of weight penalty imposed by the epa. That little chunk of metal weighs 12 pounds.

Makes sense, with a chubby chick like that, every little bit helps!

 

[inkpot]

The fluid turns into a thick nasty paste, so doesn't work properly, just binds. Playing with them would be fun, but don't see a realistic way to do it?
View attachment 1607989
View attachment 1607990
View attachment 1607991

Hmmm.... now that DOES look familiar

 

[scottryana]

Yeah I think you would have to get to it before all the fluid burns up and turns black.

I would imagine the 100 didn't get the VC because they had A-TRAC coming?

The fluid turns into a thick nasty paste, so doesn't work properly, just binds. Playing with them would be fun, but don't see a realistic way to do it?
View attachment 1607989
View attachment 1607990
View attachment 1607991

 

[excessive]

what are the symptoms of a locked VC?