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There are two differnt 249's. Older ones used the VC in hi and lo but split 50-50. Newer ones used the VC only in hi. Lo was locked. But they biased more power to the rear until the VC kicked in.

If you have the early model and want a streetable mod of the VC, then yuo could drain it (theoretically) and you would have full-time 4 hijust like the 242. Essentially operating like an open diff. Problem is no lo lock.

If you have the newer model you could do the same, but since the bias is towards the rear your open diff in the center would be more likely to lose traction on ya. You would have lo lock though.

With the newer model you have the option of taking out the front driveshaft. Actually, for a fried VC pulling the front DS is an option on the old one as well.
 
Yep, they are expensive. I had a stealership quote of $847 earlier this year. Aftermarket is $450-$600. Used ones can be found for less $50, but you have to trust how many miles are on it. You might even be able to get a unit from a junkyard for a decent price. It would be a toss up on pulling the VC or whole TC.

The operation of the 249 changed 95-96 (I'm not sure if that was the same as when the gear cut was changed) Some say the VC is different spec, others say it's the same. I don't know for sure.

Rebuilts can be iffy. Depending on the VC application, there needs to be the right spec fliud and a precise amount of air and in some they are pressurized. The air is so little in some cases that it gets tiny bubbles spread throughout the fluid, and may not be noticeable if you drain it.

How many miles? Depends on how many "lock" cycles and how many "slippages". The wear occurs during the slippage. Slippage occurs in normal driving during turns. Lock occurs when the slippage exceeds normal turning slippage. Lock is not true lock because there is still a little slippage then.

Hard to predict how many miles. I have heard ranges from 50k to 150k for VC's in general but it's gonna depend on how much it gets used. Other vehicles use VC's and the lower numbers are in designs which put the VC to use more often. They can be used in FT4x4/AWD and on-demand 4x4/AWD systems. They can also be used in a limited slip diff.

Two things are happening during the wear. The discs become slightly "polished" which means the small imperfections are worn off. Those tiny pieces of metal end up in the fluid. That gives the fluid more "grip". That extra grip is what causes the binding when a VC goes bad.

If the fluid was changed often enough, you would have completely polished discs and nothing for the fluid to grip. That's why a rebuilt can be iffy. A rebuilt (refilled) might last longer before binding, but it might not "lock" as hard. And that's assuming they get the right spec fliud and air and pressure(if any) for the application. Because of the slight polishing of the discs it will probably not be in manufacturer's specs.

Some designs have solid discs. Some have slots or holes in the discs. They don't contribute directly to grip, but do change how quickly the fluid begins to grip. BTW the fluid grips with the addition of heat caused during slippage. That's why a bad VC will not bind on short trips, not enough heat buildup. Longer trips have enough heat buildup to cause binding in the contaminated fluid.

Some tips I found for conserving the expensive VC.
-You must have the same size tire all around, even the spare. DC let some QT ZJ's out with a compact spare, there was a TSB.
-Keep the tires inflated so the actual diameter is the same all around. I used a tape measure. Depending on tire size and wear, you could find that you need a couple of PSI different pressures front and rear. Diameter is most important for VC longevity. Recheck if you go from empty cargo to heavy loaded cargo.
-If you get stuck, don't keep trying to get out if you get no or little movement. Every cycle of slip to lock causes that much more wear. Save it for when it will do ya some good. You do have tow points right?

The 249 has been labeled as bad for off-roading. It works for me. My open diffs are my problem not the VC. True lo locking is best and the later 249's have it. I suppose I would notice a problem with bigger tires and lower gears and some sort of diff traction aid.
 
MaineZJ said:
Any limit as to how far you can drive an early 249 (bad VC) with no front shaft?
Not sure. As I mentioned a VC bad enough to cause binding is locking, but never fully locked with some slippage. The worse it gets the more lock and less slip and it locks at lower temps. Slippage causes heat, I don't know how much.

Running without a front DS on an early 249 will accelerate the deterioration. It can also occur on a later 249, but due to the rear bias it occurs much slower. Theoretically, the VC will begin to lock as tight as it can as fast as it can. After that It could begin to slip more as the discs become more and more polished. I don't know how quickly that can occur.

You will never be getting 100% to the rear in any case. That translates to wasted power and fuel. Again, how much? I don't know. Maybe only a few percent loss.

Then the heat can be an issue. If there is enough, the TC fluid can be affected. Even more can cause problems with the tranny fluid, but many have tranny coolers. I don't know if enough heat will be generated. Synthetic TC fluid will fair better than dino.

If you drain the VC then weld it solid and remove the front DS you will have 2wd and 2wd lo. Throw the DS back in for PT 4wd and 4wd lo locked. Probably the cheapest way out if you have access to a welder. It would be a PITA for many though.
 
Any slip for any reason subtracts from the VC life.

Issues on swaps? Yep. There are different input shaft lenghts. There are different gear cuts. You may need different DS's. Search for this info. Its out there.
 
'95 that's when things changed. New Process became New Venture. The gear pitch was changed. The 249 gained lo lock but became an on-demand 4 hi TC. I haven't pinpointed exactly when those changes occured or if they all hapened together. You'll have to find out which you have.

Some have said that you end up with 2wd without the VC. Actually you end up with FT operation just like in th 242. It behaves like an open diff. Sure you can get the rear tires spinning but that's what an open TC would do. It would sure seem like 2wd.

Draining or removing the outer housing should produce the same result.
 
Well, I haven't drained one. The fluid is probably pretty thick. I had found that some manufacturers pump the fluid in under controlled conditions. The re-mans have some way of getting it out. I have heard of a few instances of VC failures that leaked.

I don't know if there is any handling problems with the fluid. I could even be sticky, or smell worse than used dino diff lube.

Flushing? Maybe, if not enough has come out. With what? not sure what would be the best solvent for VC fluid. We always used laquer thinner to dissolve alot of things that other solvents didn't touch. Makes a pretty good antiseptic as well, but it burns like h377.
 
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