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Unread 01-03-2010, 12:43 PM   #1
-AC-
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Shift On The Fly? What gives?

Ok, like a lot of my posts, I gotta go back in time...

As kids, with Big 3 4X4 pickups (usually early to mid 70's vintage) we NEVER tried to shift the transfer cases while moving. Just assumed you couldn't, or someone told us you couldn't, as we all assumed that the T-case would grenade.

The Mid-80's came along (an ugly time by most standards) and every company and their brother started advertising "Shift On The Fly" 4WD. Seemed like a cool inovation, and seemed to cement the idea that older 4X4's COULDN'T "Shift On The Fly".

So now I read some threads here where guys talk casually about shifting from 4HI to 2HI while driving at speed. Has this always been possible? Is it T-case specific? Specifically, can one do it with a Dana 20? What about D300? Are there rules of engagement (a poor pun, I know)?

Thanks for the knowledge...

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Unread 01-03-2010, 12:52 PM   #2
PERK
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sure, get going about 45 and say "watch this" ....drop her in low range
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Unread 01-03-2010, 01:10 PM   #3
moonpie312
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I always wondered the same thing, I mean I always thought that going from 2hi to 4hi would work, because physically your not going up or down a gear, just kicking in the front at the same speed as the rear, but of course the front hubs would have to already locked in so everything would already be spinning. But I've never tried it and probably never will, simply because I really don't see a reason to need to around here? As for going from 4hi or 2hi to 4lo while moving, that's just plain stupidity to even crack a joke about that.
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Unread 01-03-2010, 01:23 PM   #4
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No, understand that I know 4LO is OUT. But, even though the front and rear are turning at the same speed, I just always assumed, without really being told or knowing, that trying to engage the front end while that T-case is spinning at several thousand RPM's, would just be crazy.

Not so crazy?
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Unread 01-03-2010, 01:23 PM   #5
Mike Romain
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To shift into 4 low you want to be just rolling along at 1-2 mph.

To shift to 4 high, you just shift like any other shift on my Dana 300 T-case.

In the winter I leave my hubs locked which costs me 1-2 mpg if I expect snow. Then when I see snow coming, I just drop the clutch and pop it into 4 high and keep on going. See dry coming, I do the opposite, and drop to 2 high. On long intersection corners, 4 high can get up on top and plow straight same for highway ramps, so I drop to 2 high for the turn if it starts getting up on top, then back to 4 high as soon as I am out of it.

We were running at 50-55 mph yesterday on the highway in 4 high.

I have been driving it like this since 97 every winter with no issues at all.

I 'do' clean the linkage parts up and spray them with white lithium grease to keep them moving every couple years.
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Unread 01-03-2010, 01:28 PM   #6
moonpie312
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Quote:
No, understand that I know 4LO is OUT.
I figured you did know that I was just referring to the joke that PERK cracked.
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Unread 01-03-2010, 01:38 PM   #7
shok47
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Quote:
Originally Posted by Mike Romain View Post
To shift into 4 low you want to be just rolling along at 1-2 mph.

To shift to 4 high, you just shift like any other shift on my Dana 300 T-case.

In the winter I leave my hubs locked which costs me 1-2 mpg if I expect snow. Then when I see snow coming, I just drop the clutch and pop it into 4 high and keep on going. See dry coming, I do the opposite, and drop to 2 high. On long intersection corners, 4 high can get up on top and plow straight same for highway ramps, so I drop to 2 high for the turn if it starts getting up on top, then back to 4 high as soon as I am out of it.

We were running at 50-55 mph yesterday on the highway in 4 high.

I have been driving it like this since 97 every winter with no issues at all.

I 'do' clean the linkage parts up and spray them with white lithium grease to keep them moving every couple years.
mike you got some good driving tips! I remember the manual choke option as well that you do, but never pulled it off. Either that or Im doing it wrong.

My friend has a f350 powerstroke and he keeps 1 hub locked in front. Is that fine? That way he only has to lock the driver side when he gets out.


so having hubs locked without 4H in winter/slippery conditions is fine?
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Unread 01-03-2010, 02:13 PM   #8
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Actually, it was a post of Mr. Romain's in another thread that led me to ask this. I figured it was ok to roll along in 4HI at 45 or so, especially on wet/snowy roads, but I didn't know you could reach down and move between 4HI and 2HI at will. Nobody has really said yet, can you do this with a Dana 20?
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Unread 01-03-2010, 02:26 PM   #9
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Quote:
Originally Posted by -AC- View Post
Actually, it was a post of Mr. Romain's in another thread that led me to ask this. I figured it was ok to roll along in 4HI at 45 or so, especially on wet/snowy roads, but I didn't know you could reach down and move between 4HI and 2HI at will. Nobody has really said yet, can you do this with a Dana 20?
i do it with my d300 almost everyday. I would assume that the d20 is the same way but i don't know for sure.
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Unread 01-03-2010, 02:38 PM   #10
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I always did the 4 hi to 2 hi and 2hi to 4 hi with my model 20TC
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Unread 01-03-2010, 02:42 PM   #11
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Cool. Thanks!
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Unread 01-03-2010, 03:00 PM   #12
Mike Romain
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Quote:
Originally Posted by shok47 View Post
mike you got some good driving tips! I remember the manual choke option as well that you do, but never pulled it off. Either that or Im doing it wrong.

My friend has a f350 powerstroke and he keeps 1 hub locked in front. Is that fine? That way he only has to lock the driver side when he gets out.


so having hubs locked without 4H in winter/slippery conditions is fine?
Running with both hubs locked is just fine and even recommended to do once a month in the CJ owners manual to lubricate all the front parts.

I have checked it many times over the same 200 km run and it has never cost me 2 mpg, always closer to 1 mpg.

Having just one side locked is ok too, but the parts are then turning so I can't see much difference in mpg and then you still have to stop to use 4x4. If you are stuck and then have to get out to use 4x4, you are usually done and it is too late. It is best to be in 4x4 before you hit problems.

You also have to really watch the brakes! In 2 high when you hit the brakes in the snow, you just lose steering so you can pump them to try and keep control.

But and this is a Big BUT, in 4x4 when you hit the brakes in the snow, all 4 tires lock up so you go sideways faster than you can blink because the front and rear axles are locked so the proportioning valve can't work to keep the rear wheels from locking up.

The CJ owners manual says to stay off the brakes when in 4x4. This goes for on or off road. They will downshift faster than the brakes can slow them and still keep control. You only use the brakes at the very end.
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Unread 01-03-2010, 04:25 PM   #13
John Strenk
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I have never found hitting the brakes in 4X4 causes all the wheels to lock up any faster then it would in 2X4. And I've been driving jeeps since 1970. If anything, one wheel with traction will keep all the wheels turning unlike in 2X4 you can start to lock up wheels individually.

Simply, one wheel that would lock up in 2WD does not cause all 4 wheel to lock up in 4WD. In fact. the other 3 wheels would probably keep that wheel turning longer that would otherwise lock up.

Now once they all loose traction then all 4 wheels will lock up. but the point at which you lock up all 4 is a lot later than you will locking them up one or two at a time.

Now driving around in 4WD might cause you to travel faster than 2WD and you can quickly get to a point that you cannot stop your vehical in time and panic might cause you to hit the brakes harder and your momentum will cause you to lock up everything. Thats why you see a lot of SUV in the ditch off the side of a road or into the back of a Honda. I would recommend not driving any faster in 4WD THAN YOU CAN SAFELY DO IN 2wd.

And yes 2hi to 4hi to 2 hi any time, any speed. If you have different pressure in your tires though you will notice the t-case start to wind up and pop when going from 4 hi to 2 hi. You need to use the same size tires and all tires at the same pressure. If you don't you will find some tire spinning and loosing traction when the pressure builds up enough and you hit a slippery spot. This might cause you to loose control.

Another thing to watch is turning as the front wheels start tuning at a different speed than the the rear. Something has got to give so some tire, front or rear will start to spin. I like to hit tight turns in 2WD because of this. But then again how many tight turns do you hit at speed anyway but in a long 360 off ramp the difference may catch up to you.

My manual/window sticker says never to run with one hub locked. It says you will wear out components faster. It might not be that hard on a Dana 70 but a Dana 30 is pretty light weight in comparison. Like mike I never notice much difference in mpg with them locked or not. Hitting 2 or 3 extra stop lights seem to have a bigger effect.
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Unread 01-03-2010, 04:37 PM   #14
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My cj is used to plow, has a locker up front, and has the dana 20.

The dana 20 i've shifted from 2hi to 4hi rolling down the highway at 55. I just hit the clutch pull the lever (Mine is twin sticked) and let the clutch back out. Do it all the time.


As far as locking up the brakes in 4x4, i don't really notice since i avoid locking it up 98% of the time. On the rare occasion it does lock up if the whole road is slick the whole thing slides. But if one side gets traction it forcibly spins the other side because of the locker.

Take it for what it's worth as with all internet information
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Unread 01-03-2010, 04:40 PM   #15
John Strenk
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Plus, as I'm sure you notice as I have with my plow, adding 800# to the front ends tends to give you a little more traction up front.

I don't even bother with the clutch to go from 2 to 4 unless some end is spinning.
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