Shifting "On-the-Fly"

[SafeAirOne]

How fast can one be going in 2 wheel drive before shifting into 4 high? I've done it at low speeds (below say...7-10mph), but I don't wan't to do it at higher speeds, in situations where you want to conserve momentum, for fear of busting something.

[greenmeanie]

You are essentially mating a dog clutch when you engage 4wd. With this in minfd you have a very simple tooth design and not a lot of them that you are trying to mate together which creates shock loads. Shock loads are what will kill the dog teeth.

In theory if everything was equal then everything will be spinning at the same speed and it should not be too bad. In reality it is a very easy way to destroy the transfer case as there is always some disparity between the front and rear of the truck.

At the very least you will greatly accelerate the wear of the dog clutch. I generally consider human running speed to be about the speed limit.

[Jeff Aronson]

As recommended by GreenMeanie, it makes a lot of sense to shift into 4 high before you're hitting high speeds.

That said, I've done it at 45-50 mph when road conditions warranted the change, i.e., from dry to snow covered and slick, with no evident problems. I've learned not to be prodded by foolish drivers insisting on 70 mph speeds on snow covered interstates. Remember that 4wd does not overrule the laws of physics.

Jeff

[JSBriggs]

.... Remember that 4wd does not overrule the laws of physics.

Jeff

Or the laws of Murphy!

-Jeff

[daveb]

Any speed of your choosing as long as you are headed in a straight line and don't have disengaged freewheel hubs. Never had any problems at 35-40 on snowy roads. Putting the clutch in helps a little if you are very concerned.

How fast can one be going in 2 wheel drive before shifting into 4 high? I've done it at low speeds (below say...7-10mph), but I don't wan't to do it at higher speeds, in situations where you want to conserve momentum, for fear of busting something.

[SafeAirOne]

Thanks for all the input. It sound as if I should proceed as I have been; Namely, at a low speed, de-clutch, then shove yellow knob down, smoothly reapply throttle/clutch.

The thing that prompted the question in the first place is that I have to turn off a 2-wheel drive, mostly dry street to a sometimes snow-covered steep hill to get to my mother's house. I'd rather not start up the hill from a dead stop if I can help it. Plus, the 4 high engages so seamlessly at low speeds that I wondered how fast the works can be spinning and still engage gracefully. Glad to hear it's been done at speeds of 30-50 in a straight line with a slippery road surface under the wheels.

[Oscar]

But, you don't want to make that turn on the dry road in 4WD if you can help it.....