aerostar transfer case
Lead Driver
Joined: Sep 2003
Posts: 7,013
Likes: 205
From: SoCal
The real problem with driving on pavement in full locked mode is that the turn radii of all 4 wheels are different in a turn. So even with identically sized tires, the drivetrain will bind going through a turn. I found this out recently when my 4wd system malfunctioned and kept the transfer case locked. I like the idea of a manual over-ride to force the system into full open or full lock as needed. A lot of older 4wd vehicles work this way. I once drive a Mercedes Galundenwagen with 3 locking levers; one for manually locking each diff in the car.
Senior User
Joined: Feb 2004
Posts: 389
Likes: 0
From: Rochester, NY
That's the reason that most vehicles with factory-issued locking diffs (like an Audi 4000, for example) have them auto-disengage above a given (usually pretty low) speed.
If you lock an axle diff on the street, you will bind the axle in a turn, but if you make roughly the same number of turns on average is each direction it more or less cancels out. You can often go a long way without doing any major harm. With a center lock, though, it's a different story. The front end of the vehicle always goes around a larger radius turn then the rear, regardless of the direction of turn. So it will not self-unbind like an axle might. The more you turn, the more you will wind torque into the drivetrain. That can lead to a bad situation in a hurry. It could cause an actual part failure that might leave you stuck. The wind-up might also compromise your ability to steer the vehicle well. So you would definately have to make sure you remembered to unlock the diff when not needed...
If you lock an axle diff on the street, you will bind the axle in a turn, but if you make roughly the same number of turns on average is each direction it more or less cancels out. You can often go a long way without doing any major harm. With a center lock, though, it's a different story. The front end of the vehicle always goes around a larger radius turn then the rear, regardless of the direction of turn. So it will not self-unbind like an axle might. The more you turn, the more you will wind torque into the drivetrain. That can lead to a bad situation in a hurry. It could cause an actual part failure that might leave you stuck. The wind-up might also compromise your ability to steer the vehicle well. So you would definately have to make sure you remembered to unlock the diff when not needed...
New User
Joined: Dec 2003
Posts: 24
Likes: 0
From: Monroe WA
Originally Posted by rchouser
This may be something better handled with the PM environment, but, here goes anyway. The idea of a switch by passing/overriding the computer input and giving me control to go to 50/50 before I slip is of use to me. I backed up over a curb onto my "lawn" to place my tail gate close to my "load". The rear wheels climbed the curb well with the 30% push from the front. When I eased the front wheels to the same curb, I had to "spin" the rear wheels first before I got the 50/50 allowing the front wheels to climb the same curb. If I had had an over-ride available, I would not have had to "force the spin". Aside from gas milage, what is the problem with running 50/50 on demand. Could the computer be tricked into complacency (not damaged)? It seems that it would be relatively simple to imput the correct amperage to activate the servo (or whatever switching mechanism is used to activate the electromagnetic clutch). What would be the down side of this. thanks chad
Would be nice to lock it up.
Originally Posted by copper_90680
The downside is when you forget to turn off the switch and drive with the clutch fully engaged. It'll probably overheat your clutch coil and, if you are driving on asphalt, it'll most likely damage your drivetrain due to mismatches in tire diameters between front and rear. If you must do it, I'd recommend a push-button momentary switch, but then it'll be hard to drive with one hand while the other hand is on the switch 
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